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Bob McDavitt's ideas for sailing weather around the South pacific

25 December 2009

BOBGRAM7 issued 26 Dec 2009

WEATHERGRAM
YOTREPS
Issued 26 December 2009
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

TROPICS
This edition is earlier than normal and next one will be later than normal as I'll be travelling around during next week.

It looks to me as if we will have another reasonably quiet week in the South Pacific.
South Pacific Convergence zone SPCZ has split into three entities, but maybe they are still linked in some way.

Convergence zone1 is active in eastern Coral Sea, but this may weaken this week. Convergence zone2 extends from Tokelau to Southern Cooks. A tropical LOW within this zone is likely to cross the Southern cooks on Mon 28 Dec UTC and then deepen as it peels off to the southeast, stealing away the wind from the tropics.

A third convergence zone is draped over French Polynesia and will hover around there all week, this often happens in an El Nino.

SUBTROPICS
HIGH just north of NZ today is blocked and will fade where it is by Wednesday.
The enhanced trade winds on its northern side from Niue to New Caledonia and NE winds from New Caledonia to Queensland will also fade.

Next High rolling in from the eats is likely to cross Tasmania on Tuesday 29 Dec, killing the wind for the Sydney-Hobart racers, and then move northeast across the Tasman Sea and reach Northern North Island on 1 January. So that Tasman Sea pattern is almost a repeat if last week's.
This High should be able to get further east than its predecessor along 30 South during 1-2-3 January, so that then the enhanced trade winds on its northern side may extend from French Polynesia to New Caledonia, and the SPCZ may reform along 10 South.

NEW ZEALAND AREA:
Fronts have been side-swiping southern NZ during past week, knocking on the door but higher pressures have killed them.
Now that the High over northern NZ is expected to have dropping pressures, the next front should be able to open the door and spread across NZ – preceded by strong NW winds, crossing South Island on Tuesday and North Island on Wednesday, and be followed by a strong cooling SW flow until Thursday. Then the idea is for a disturbed westerly flow for a few days.

I'll leave you all with these last few verses from Robbie Burns to mark the finish of the first decade of the second millennium:

We two have paddled in the stream,
from morning sun till dine† ;
But seas between us broad have roared
since the days of auld lang syne.

For auld lang syne, my friend,
for auld lang syne,
we'll take a cup of kindness yet,
for the sake of auld lang syne.

And here's a hand my trusty friend!
And give us a hand o' thine!
And we'll take a right good-will draught, for the sake of auld lang syne.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

19 December 2009

BOBGRAM7 issued 20 Dec 2009

WEATHERGRAM
YOTREPS
Issued 20 December 2009
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Cyclone MICK took with it a lot of the convective energy that had been
building up over recent weeks, and has left behind a very quiet South
pacific convergence zone SPCZ. This zone is now rebuilding along 10S
between Tokelau and Northern Cooks, and is expected this week to shift
more to 15-20S between Samoa and French Polynesia. Computer output
suggests a LOW forming on the SPCZ around French Polynesia on Tuesday 22
Dec UTC and then moving to the south of the group on Christmas Day.
Avoid.

There is still some of the old SPCZ convection around Vanuatu , and this
is expected to wander around the region all week in a disorganised
fashion.

SUBTROPICS
MICK dived into the subtropics last week and has "stolen" much of the
trade winds and disrupted the position of the subtropical ridge. The
next high roiling in from the west is over the Tasmanian area today and
is likely to take a track more common for highs at this time of the year
- we have the summer solstice on Tuesday 22 Dec= the longest day, and
meant to be the start of the southern most tracks for subtropical ridge.
This High is expected to cross the North island / 40S on Tuesday 22 Dec
and then nose into the South Pacific along 30 to 40S steadily holing
itself together as a single entity until 30 Dec. Reliable and
dependable.

As this High slides east it will bring the trade winds back from
southern French Polynesia all the way to the Coral Sea. There may even
be a small squash zone on the northern side of this high, along 25 to
30S between 160W and 180 from 23 to 28 Dec.

NEW ZEALAND AREA:
During a lead up to Christmas over NZ there is a dying southerly flow on
Monday 21 Dec, and then the passage of that High with light winds and
generally settled weather. On Wed 23 Dec, as the High is crossing the
North Island, some converging sea breezes may combine with cold air
aloft to make afternoon heat showers/intense downpours around Bay of
Plenty.

If people here can still remember the weather they had last Fri, 18 Dec,
then it looks like something similar will be happening to then Fri 25
Dec, for that's when the next front, in cahoots with the central
Australian heat trough, will be moving from Tasman Sea onto southern NZ,
preceded by a NW flow, kicking away the High further north. Some
differences also: the NW wind may not be as strong, and in central
Australia by then will be the remains of Cyclone LAURENCE.

Christmas reminds us of the miracle of new creation and the purpose of
living life to it fullest. Festive cheer is part of this process, so
feast cheerfully folks.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

12 December 2009

BOBGRAM7 issued 13 Dec 2009

WEATHERGRAM
YOTREPS
Issued 13 December 2009
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

The past week was indeed busy with deep convection between Solomons and
Tuvalu, and all this has wound into the first tropical cyclone of the
season for the South Pacific. It has earned a name for itself: MICK.
This is expected to move southeast, across Fiji on Monday and Tonga on
Tuesday with gale winds, then further off into the southern Ocean, south
along 160W. AVOID.

Further east: the South Pacific Convergence zone SPCZ has been south of
its norm position lying along 20South between Niue and South of French
Polynesia, and is expected to stay in much the same place this week and
slowly fade. In tandem with this zone there is a subtropical ridge
between 35 and 40S.in the eastern end of the South Pacific.

Some computer models are picking that a tropical cyclone may form off
the NW Australian Coast from Tuesday onwards and it may go south and
inland on weekend 19/20 Dec-details still uncertain - if that may bother
you then stay up to date.

SUBTROPICS
A HIGH is expected to cross Tasmanian on Monday and then move northeast
across the Tasman Sea on 15-16-17 Dec, enhancing the trade winds on its
northern side and in the Cora Sea. This High should then move east,
and, once MICK gets out of the way, get past the dateline along the
subtropics at 30 to 35S from 18 to 21 Dec, enhancing the trade winds
between Fiji and Southern Cooks, and encouraging a new SPCZ to form
between Coral Sea and French Polynesia

NEW ZEALAND AREA:
Mediocrity: A trough is expected to cross NZ on Monday/Tuesday followed
by anticyclonic southwest flow on Wednesday/ Thursday, then, on Friday,
a strong NW flow followed by a front for the South Island. This front
should slow down and weaken over the North Island on the 19/20 weekend,
and another front is expected to move onto the South Island from the
southwest on Sunday 20 Dec.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

05 December 2009

BOBGRAM7 issued 6 Dec 2009

WEATHERGRAM
YOTREPS
Issued 6 December 2009
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Sadly the Satellite that has been helping us out with sea winds
(Scatterometer) over the past decade has died--- the bearing which spin
its mirrors were only made to last 5 years, and they seized after 10
years , so no more data. I have not been informed of any replacement
plans at this stage, so in the meantime my ability to check wind over
the ocean is not as good as it was.

The wettest part of the planet last week has been along the Pacific
equator, between 160E and 180. There is a ship near by this region
reporting strong westerlies, so we can assume that is a surge of
equatorial westerly winds. Hold on to your hats in Kiribati, the swell
will possibly keep you in side harbour this week.

This could be an active week near the dateline:
Rain in the South Pacific convergence zone has also been active between
Solomons and Vanuatu and around the North Coral Sea. The SPCZ also lies
along a zone from Samoa to French Polynesia. Computer models are
latching on the area between northern Vanuatu and Tuvalu as a likely
breeding ground for Tropical lows this week, but lows breeding in this
region are likely to be slow-moving. There is already a large zone
below 1005 in that region. This is likely to feed off the equatorial
westerlies and bring strong NW winds across Tuvalu, Tokelau and Samoa.
Once these NW winds reach Tokelau-around Tue 8 Dec UTC, that may fire up
a rapidly deepening tropical low system between Tuvalu and Samoa on Wed
9 Dec, and then that system will likely travel SSE near Wallis /Futuna
on Thu 10 Dec and then across Northern Tonga on Fri 11 Dec where it may
well earn a name for itself. Avoid.

SUBTROPICS
A good sized high is dominating the subtropical ridge along 30S from 180
to 140W at present and this has enhanced trade winds on its northern
side. This high is expected to fade by Thu 3 Dec, allowing a trough to
spread east. Following this trough there is expected to be a new high
spreading east of NZ along 40S, thus taking the subtropical ridge
southwards this week.

TASMAN SEA / NZ AREA
Subtropical air brought some welcome but briefly intense rain to our
North Island last week. The SW Pacific subtropics are now shifting back
to around 30S again for at least the next fortnight.

SO it is back to the disturbed westerly pattern over NZ, but the fronts
are likely to weaken as the move across the country-one on Tue 8 Dec
just raining on southwest fringes, another on Wed 9 Dec more noticeable
over South Island, and a third on Fri/Sat/Sun 11/12/13 Dec bringing a
southerly wind change to eastern areas.

The fronts 8, 9 and 11 should be preceded by strong NW winds
concentrating rain on Alps and bringing some hot dry winds further east.


Around Sun 13 Dec, a High is likely to cross Tasmania and this should
shovel a cold front north on Mon/Tue 14/15 Dec feeding in a cold
southerly blast onto NZ and further north. If you are trying to sail
into Northland from the north then winds will be more useful for
landfall before Sun 13 Dec rather than after.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

28 November 2009

BOBGRAM6 issued 29 Nov 2009

WEATHERGRAM
YOTREPS
Issued 29 November 2009
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Tropical cyclone NIDA spend last week wandering off to the north of Yap
Island.

There is an equatorial westerly burst today 29 Nov and this is likely to
make another tropical low over Micronesia area during the week-but is
NOT expected to reach Nauru/Kiribati. The Low should deepen as it moves
north and may reach Guam area by around 9 Dec.

Another equatorial westerly burst in expected just north of Papua New
Guinea/Solomons from 9 to 12 Dec.

The South Pacific Convergence zone stretches from the Northern Coral
Sea/ northern Vanuatu area to around Tokelau/ Samoa and then
southeastwards to between southern Cooks and French Polynesia. The
section around Southern cooks is likely to get more active from Thu 3
Dec UTC. Vaguely related to the SPCZ, a LOW is expected to form near
25S 130W around Thu 3 Dec UTC ... something for Pitcairn's to be aware
about.

SUBTROPICS
A good sized high is dominating the subtropical ridge along 30S from 180
to 140W at present and this has enhanced trade winds on its northern
side. This high is expected to fade by Thu 3 Dec, allowing a trough to
spread east. Following this trough there is expected to be a new high
spreading east of NZ along 40S, thus taking the subtropical ridge
southwards this week.

TASMAN SEA / NZ AREA
The subtropical ridge is shifting south this week making a pattern
change in NZ away from the El Nino southwest outbreaks of the past
month.

So this week is different: a trough with several little lows is
expected to cross central NZ on Monday, Tuesday, and Wednesday 30 Nov-2
Dec. The key to the pattern change is the High that is expected to zip
across the south Tasman Sea on Tuesday and Wednesday 1-2 Dec and then
expand east of NZ along 40S on Thursday Friday 3-4 Dec. As this High
bubs east the remains of that moist trough are expected to fade over the
North Island - so that by the weekend 5-6 Dec a moist humid northerly
flow should encompass NZ for a few days. This is a good way to start the
calendar months of summer.

A brief SW change is expected over Northland around Mon 7 Dec, but
generally this new pattern enables some good voyaging form Tonga and
Fiji to NZ for anyone still looking.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

22 November 2009

BOBGRAM7 issued 22 Nov

WEATHERGRAM
YOTREPS
Issued 22 November 2009
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Tropical cyclone ANJA faded east of Mauritius during the past week.
The South Pacific Convergence zone stretches from the Northern Coral
Sea/ northern Vanuatu area to around Tuvalu to Tokelau and then
southeastwards between northern and southern Cooks and then across
southern islands of French Polynesia FP.

A small low is expected to form in the SPCZ around southern FP on Mon 23
Nov UTC and wander off to the south - some clockwise winds with this low
and it is likely to be followed by a wind flow from the north or
northeast over FP.

SPCZ is expected to get active this week west of the dateline, in
response to the travel of a Madden Julian Oscillation MJO from Indonesia
to the Papua New Guinea/Solomons area. SPCZ may take a trip south
towards Fiji and Tonga on the 27/28 /29 Nov weekend, according to
today's run of the NOGAPS model-bringing them some now-welcome rain.
Other models say no.

The trough which crossed NZ this weekend (dropping temperature in Timaru
from 28 to 15 C at Saturday brunch in typical Canterbury spring fashion)
is expected to help trigger a low south of southern Cooks near 30S 160W
on Mon/Tue 23/24 Nov. This Low will "steal the wind" between the Cooks
and Niue as the low itself moves off to the south from Tue 24 to
Thursday 26 Nov.

TASMAN SEA / NZ AREA
The upper atmosphere has been encouraging highs over South Australia and
Tasmania and lows around Chatham Islands. These highs have built
heat-wave conditions over South Australia. The combination of highs to
the west and lows to the east has encouraged cold southwest outbreaks
over NZ - a typical El Nino spring scenario.

This coming week is offering more of this pattern, but with a
slow-moving high that may well touch Northland.

The high in the north Tasman Sea today 22 Nov is expected to fade there
by Tuesday 24 Nov, as a front and SW flow spreads over NZ on 25 Nov,
severe in the south.

A new High is expected to squeeze along 35S from Australian Bight to
Tasman Sea on Tues 24 Nov, and then noodle northwards across the Tasman
Se on Tue to Thu 24 to 26 Nov so that it stretches west to east along
30S between NZ and Fiji from Thu 26 Nov to Mon 30 Nov. There is likely
to be a squash zone of enhanced trade winds to north of this high - in
Coral sea from 24 to 26 Nov and extending from Fiji to French Polynesia
from 26 to 30 Nov.

On Fri 27 Nov a low at 50S in the Southern Ocean may deepen as it passes
by, making for another vigorous SW blast over southern NZ.

Lows are also expected to deepen in west Tasman Sea on Fri 27 Nov and
Sat 28 Nov and cross central NZ on Sat/Sun/Mon/Tue 28/29 Nov and 1 and 2
Dec. Avoid these lows. Also these lows may trigger a change in the "SW
pattern" that has been affecting NZ over last month or so.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

14 November 2009

BOBGRAM7 issued 15 Nov 2009

WEATHERGRAM
YOTREPS
Issued 15 November 2009
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Tropical cyclone ANJA in the South Indian Ocean has started the Southern
Hemisphere cyclone off. It was perhaps helped by a pulse of extra
convection called a Madden Julian Oscillation, and this pulse is
expected to reach the equatorial western pacific around 20 to 30 Nov...
so the next few days marks the end of a relatively quiet period for the
South Pacific Convergence Zone SPCZ and next week may mark the beginning
of some extra convection in our part of the world.

Those cruising yachts still looking for a trouble-free trip to NZ or
Australia had better set off this week.

SPCZ has recently been extending from Solomons/Northern Coral Sea to
northern Vanuatu and from Tuvalu to Samoa to French Polynesia FP.

The section over FP is likely to develop a small tropical low or two
on Mon -Tue 16-17 Nov, UTC, and this will then peel off to the
southeast, leaving behind typical convergence zone conditions of light
variable winds and a few tropical squalls.

A branch of the SPCZ in the Coral Sea is likely to spread across Vanuatu
and New Caledonia from now to Tuesday 17 Nov and then fade. This zone
is embedded in a easterly flow ,around 10 knots on the north side of the
zone, around 20 knots on south end of zone and squally within the SPCZ.

The branch from Tuvalu across Samoa to FP should stay in place this
week, with ENE winds 10 knots on its northern side. SE winds 15 to 20
knots on its southern side and squally within a 5 to 7 degree wide zone.


Less wind in the Coral Sea than there has been over past few weeks.

TASMAN SEA/NZ
HIGH fills the subtropics along 28S from 160E to 160W today is expected
to turn into a wind flow from the east in the area west of the dateline
by Tuesday 17 Nov, and in the areas east of the dateline by Friday 20
Nov. This makes sailing south to NZ or west to Australia a reasonable
prospect this week. Go for it before the MJO turns up J

LOW is expected to cross Tasmania on Monday 16 Nov and then peak in the
central Tasman on Tue 17 Nov and cross NZ on wed 18 Nov and then fade
over Chatham Islands on Thu 19 Nov. The NW flow ahead of its front may
be useful for yachts making landfall in Northland early on Tue 17 Nov.
However the SW winds around Northland on Wed-Thu 18-19 Nov will be in
the face of incoming boats.

Next HIGH is expected to take a path further south than the last-may
bring some warmth with it. Should cross Bass Strait on Tue 17 Nov,
central Tasman Sea on wed 18 to Fri 20 Nov, and then have centres west
and east of North Island on Sat-Sun 21-22 Nov. OK for sailing south-may
have to motor near Northland on Fri-Sat 20-21 Nov.

South of this High, a passing front should bring strong NW winds to
southern NZ on Fri-Sat 20-21 Nov along 35S


I will be at Swordfish Club in Russell around 5:30pm this sat evening 21
Nov, talking LOCAL WEATHER.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

07 November 2009

BOBGRAM7 issued 8 Nov 2009

WEATHERGRAM
YOTREPS
Issued 8 November 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

There were 22 yachts at north Minerva last Tuesday as this spring's
yacht-migration hits peak. The wind flow around Northland has been
generally from the southwest over the past week - occasionally from the
south or southeast following a few fronts, and there has been a large
zone of calm along the subtropical ridge neat 30S, so weather has been
suitably challenging and produced some stints of analysis paralysis at
the Minerva marina.

Northern Hemisphere is still producing tropical cyclones: IDA started
in central America and now expected to build briefly over Gulf of
Mexico, and a TC called TWENTYFIVE is wandering northeast away from
Micronesia.

On our side of the equator, our South Pacific Convergence Zone SPCZ is
now entering a quiet period. During the past week it extended from
Solomons to Wallis/Futuna to northern Tonga to Northern Cooks. During
9-12 Nov UTC a piece of this zone is expected to go southeast to south
of French Polynesia FP and briefly become a low system, stealing the
wind from FP for a few days.

Another piece is likely to drift southwards towards Fiji and Tonga on
10-13 Nov. Otherwise I think this is a week where the main SPCZ will be
hugging 10S.

Because of HIGH pressures in the Tasman Sea, strong winds are expected
to continue all week across the Coral Sea. This squash zone covers
central parts of Vanuatu and extends to Fiji at times.

TASMAN SEA/NZ
During a brief gap between Highs a few days ago, the Queensland heat
trough was able to ingest some moist air from the Tasman Sea and dump it
onto Coffs harbour area on Friday: their fifth flood this year.

Highs are continuing to linger and fade in the Tasman Sea. It is as if
the New Zealand's southern door has been left open allowing
fronts/troughs to roll onto NZ from the southern ocean: one on Monday 9,
one on Wednesday 11 and one of Friday/Saturday 13-14, each slightly
cooler than the one before. There seems to be some Antarctic melt water
around Macquarie Island at present- a large iceberg was seen passing by
there late last week.

Watch the wind: There is likely to be a deep low passing by in the
southern ocean on Sat 14, and that should make for very strong winds in
central and southern NZ areas this weekend.

As for the HIGHS, today's Tasman High got over 1036 but should move into
the north Tasman Sea during the week and fade away by Thursday 12 Nov.
In the gap-between-the-highs the forecast, at present, is that we don't
get a repeat of last week's Coffs harbour flood. This time a low is
likely to form off the southern New South Wales Coast on Thursday 12
Nov, then deepen a little between Lord Howe and Norfolk Islands on Fri
13 Nov, then fade as it goes northeast.

This low should be followed by another High crossing Bass Strait on Fri
13 Nov, then heading northeastwards.

Next week, from around 16 Nov, this high should be east of Northland and
a NW flow is finally likely over Northland, making landfall slightly
easier for a few days.

Note that I'll be attending to the MetService display at Royal Show in
Christchurch this week, so may not be able to respond easily to emails.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

01 November 2009

BOBGRAM7 issued 1 NOV 2009

WEATHERGRAM
YOTREPS
Issued 1 November 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

As the calendar ticks into the month that is regarded as the start of
the cyclone season, and into the traditional time that yacht weather
damage is not covered by insurance in the tropics of the Southern
Hemisphere, yachts tend to migrate from the South Pacific Islands to New
Zealand or Australia.

There have been four damaging cyclones over the Philippines in the past
month-one a week-so the Northern Hemisphere cyclone season is still
having its last hurrah.

The South Pacific Convergence Zone SPCZ was more active than normal in
the past few weeks-and had some northwest winds on its northern side
making for troughing conditions-briefly a LOW formed on it in the Coral
Sea, but it appears to be easing now. It is draped from Coral Sea
across northern Vanuatu to Wallis and Futuna to northern Tong and then
southeastwards to be sort of mid-way between Southern Cooks and French
Polynesia. A small low might form on the SPCZ to south of southern
Cooks around Fri 6 November, but if it does it will just peel off to the
southeast and fade.

It looks as though the SPCZ may move a little south this week, perhaps
reaching Fiji on Tuesday 3 Nov and southern Tonga on 4 to 5 Nov, but it
also appears to be fading.

So the cyclone season starts with a low risk of any disturbances this
week.


CROSSING THE SUBTROPICS and HEADING FOR NZ The subtropical HIGHS
dominate proceedings this week, basically killing the wind along 30S.
Heading for NZ this week from Tonga or Fiji is good for motor vessels,
but yachts looking for sailing winds all the way should wait until next
week, maybe longer.

One HIGH is already in evidence on the central Tasman Sea and should
slowly get into the north Tasman Sea on Monday Tuesday 2-3 Nov and then
slide east along 30S as it fades on Wednesday/Thursday 4-5 November.
There will be a small but noticeable increase in the trade winds over
Fiji and Tonga on Wed and Thursday 4-5 Nov as this High glides by - a
small squash zone.

On Friday to Monday 6 to 9 Nov, and maybe longer, a new HIGH is expected
to build in the Tasman Sea, enhancing the trade winds between New
Caledonia and Queensland.


Between these highs, on 4 and 5 Nov, a heat trough is likely to over
inland Queensland, turning winds along its coast to come in from the
northeast.

Through all this, all week, New Zealand should remain in a disturbed
southwest flow, with one front crossing on Mon-Tues 2-3 Nov, another on
Wed-Thu 4-5 Nov, and a third brushing past the South Island on Friday 6
Nov. Boats heading for Northland should find Wednesday or Friday and
Saturday will be the best days to make landfall.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

25 October 2009

BOBGRAM7 issued 25 Oct 2009

WEATHERGRAM
YOTREPS
Issued 25 October 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

NIWA, Fiji Met Service and BoM have all produced much the same outlook
for the coming cyclone season. The El Nino observed in the Ocean was
not having much impact on weather patterns in the atmosphere as measured
by the SOI (until the last week or so). Computers are expecting the
main coupling between ocean and atmosphere to occur around December and
January. Indications are for around 8 cyclones in the South West
Pacific this season (the normal is 9). Countries east of 180 are at a
higher risk than normal. 2 or 3 cyclones may reach at least Category 3
and one may reach at least category 4. The first storm is likely to
develop before the end of December.

There are still cyclones in the Northern Hemisphere-LUPIT near eastern
Japan and NEKI over western islands of Hawaii. Last weeks burst of
equatorial westerlies last extended eastwards to beyond 170E and is
likely to affect Kiribati and Tuvalu this week, affecting west-facing
harbours.

South pacific convergence zone, hugging 10S between Solomons and
Tokelau, has west to northwest winds on its northern side and a squash
zone of trade winds on its southern side along 15S. The SPCZ is showing
signs of moving south and may extend as far south as Fiji by Wednesday
28 Oct, perhaps developing a low between Samoa and northern Tonga that
will extend southeast wards across southern Cooks by 30 Oct UTC... Also
SPCZ may develop a low in the Coral Sea, south of Solomons on 27 Oct
that may stall and then shift west-wards and fade away around 31 Oct
UTC. In any event, the strong SE winds in the central Coral Sea and
expected to last all week.

SO the SPCZ is worth avoiding this week.

CROSSING THE SUBTROPICS and HEADING FOR NZ ... Maybe not this week...
High pressures in the Tasman Sea this week and low pressures to east of
NZ team together so that we have south and southwest winds between NZ
and Tonga over next few days and so no offering of a good sail. This
southwesterly is expected to reach Minerva around Tuesday 27 Oct and
Nukualofa around Wednesday 28 Oct and last around 2 days so that the
next "weather window" for departing from Tonga NZ may open around Friday
30 Oct, perhaps a little later. .

Approaching NZ from New Caledonia or from Australia may be OK this week,
but avoid the SW flow near the North Island on Tuesday and Thursday -
passing fronts may have gale winds and high seas.

In detail: A LOW is forecast to deepen as it crosses central NZ on
Monday and as a HIGH forms in the South Tasman Sea - so that a SW gale
in-between these systems focuses in the area west of the North Island
and reaches a peak Tuesday UTC. The High then fades and stalls on
Wednesday as the Low moves off the east and weakens. But by late
Wednesday and during Thursday a trough deepens east of and over NZ as a
new High builds in the Tasman Sea - in-between will be a vigorous cold
polar outbreak of southerly winds.

That new High is forecast to cross NZ on Sunday and Monday bringing NZ a
break in the SW weather.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

17 October 2009

BOBGRAM6 issued 18 Oct 2009

WEATHERGRAM
YOTREPS
Issued 18 October 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

We are now entering the migration season when several yachts shift in
the Southern Hemisphere from Tropical to middle latitudes.

There are still cyclones forming in the NW Pacific, LUPIT, and near
Mexico , RICK. There was burst of equatorial westerlies to north of
Papua New Guinea for much of last week, and an attempt at forming a TC
just north of Solomons, but nope, not yet. It looks as though South
Pacific will not be ready for a few weeks yet, maybe a month or more.

The ocean temperatures are consistent with an El Nino episode; the
Southern Oscillation index is hovering around neutral but starting to
lean in an El Nino direction. NIWA (NZ) and BoM (OZ) will be issuing
their cyclone outlook this week at
http://www.bom.gov.au/weather/cyclone/NatOutlookNotice.pdf
and (NIWA's Island Climate Update for Oct) at
http://www.niwa.co.nz/our-science/climate/publications/all/icu

South Pacific Convergence Zone SPCZ has been most active across the PNG/
Solomons doldrums area and then along 10S as far as Tokelau and then
between the Northern and Southern Cooks and across French Polynesia.
This location is further north and east than normal, as found in a El
Nino episode. Most likely the SPCZ will be drifting south over next few
weeks...should visit Samoa on 20 Oct, and Wallis/Futuna/northern Tonga
on 22-25 Oct, and Fiji/Southern Tonga on 26-28 Oct.

Winds in the Coral Sea have been strong SE last week and will be strong
SE until 24 Oct due to high pressure in the Tasman Sea. Anyone sailing
Vanuatu /New Caledonia to Australia this week are in for a bouncy rides.


CROSSING THE SUBTROPICS and HEADING FOR NZ

The thing to do when planning such a trip is to avoid squash zones
(where isobars are squeezed together as highs go by) and fronts. Try to
reach Northland between fronts - that means working out the average
timing of fronts reaching Northland. This is hard because weather
output is only good for a few days and your trip may take a week.
Usually if you deliberately arrange to go thru a front at 30S (where
they are usually weak) then that will give you a gap between fronts for
your landfall.

This week the subtropical high is the main features to watch............


The High forming offshore Sydney on Mon 19th is expected to move NE and
stall near Norfolk Island on 22 Oct. It will need to wait for a series
of fronts and troughs to make their way NE across eastern NZ, one on 19,
and another on 21 to 23 Oct --- so much of this week there will be
southerly winds over Northland (between Tasman high and the troughs to
the east).

However, after 23 Oct, that High is expected to poke its tongue out and
along 33S, followed by a NW flow -making a reasonable wind for landfall
in Northland for sailing from New Caledonia/Fiji/Tonga between 24 and 27
Oct. At this stage this window closes over Northland, for those coming
from Tonga anyway, around 28 Oct when next trough is expected to reach
Northland.

To work in with this window you will need to arrange to get to the
subtropical ridge (30-33S) by around 23 Oct.

For those in New Caledonia: there will be something of a squash zone of
the north side of that high when it is in the central Tasman Sea, so
you may need to sail SSW first when heading to NZ.

For those in NZ looking forward to the Coastal Classic:
Front reaching Auckland on Friday morning is the last in a series of
fronts and should be followed by that High then near Norfolk Island.
SO, at this stage, the outlook if for a stiff SW wind that may weaken
Friday night and briefly swing SE. EC model makes more of this SE at
present than do the other models, so it may be a fast race.

The current EC model deepens a low off Sydney on Sun 25 Oct --- this has
only a 30% chance of happening at this stage, so recheck.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

11 October 2009

BOBGRAM7 issued 11 Oct 2009

WEATHERGRAM
YOTREPS
Issued 11 October 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Vanuatu Quake--- this was a sideways shake so didn't toss the sea around
too much. Phew.

Palolo (or Balolo in Fiji): These worms rise out of the coral reefs for
a spawn-fest in the waning moon of Oct and Nov (around now), that's if
they haven't been upset by recent events. Anyway ask the locals,
something to do while waiting for a good voyage south,

Northwest pacific cyclone season - because the names used tin that
region cover several language with different scripts they don't go
alphabetically in the English alphabet after all. Thanks to those who
picked me up on my surprise at the jump from KETSANA to PARMAR/MELOR
last week.

MELOR was a real super cyclone for a while and managed to mostly miss
Guam, then smashed into south-eastern Japan, killing 5 and injuring
around 100.

In the South Pacific the Convergence Zone SPCZ has split into two, with
one branch from around Solomons to near Fiji, and another branch from
Tokelau across Northern cooks and touching between central French
Polynesia and Marquesas-a rare northeastern position for the SPCZ.

I think the western branch will move onto Tonga around mid week, and a
Low may form between Tonga and Niue on 14 Oct then move southeast and
deepen as it feeds off an upper jet stream. SO that may keep yachts in
Tonga while yet.

There has been an equatorial westerly during the last week between
Solomons and Micronesia, and GFS model is trying to produce a Low over
the Solomons area out of this later this week... but EC model doesn't.
In this case I'm inclined to agree with the EC.

Winds in the northern Coral Sea were strong last week but should relax
over next few days as a trough crosses the Tasman. They are likely to
get strong again
For 17 to 24 Oct as another High crosses the Tasman and this strong wind
zone is likely to affect New Caledonia from 18 to 22 or 23 Oct, so see
if that times in with your plans around there.


TONGA to NZ/ CROSSING THE SUBTROPICS
As said before- a weak part of SPCZ should visit south Tonga around
12-13 Oct and a low may form on this near Niue on 14 Oct. If you are
already at Minerva you may miss this, or perhaps can see it overhead
tonight.

In tandem with this, the HIGH over Tasman Sea today already pokes a
tongue of ridge towards NE of North Island and should travel east along
this axis maintaining a reasonable subtropical ridge between Tonga and
NZ, at 30S anyway, until 17 Oct. Although this is a nice enough ridge
to sail across the subtropics with, the problem is timing - it will get
you to NZ just when the next big trough arrives, frontal zone around 17
oct followed by a couple of days of SW to S winds. Either avoid or work
out a coping path.

BTW this trough is likely to breed a 988 Low over Tasmania in Tuesday,
avoid. Its first front should cross NZ on Wed 14 Oct and may be
somewhat thundery, announcing the return to spring over NZ after 3
winter-like lows.

Next HIGH from Australian bight should cross New South Wales on 17-18
Oct and Tasman on 19-21 Oct. So there is a possible window: a yacht
capable of up to 6 knots could possibly depart Vavau around 14 Oct, go
thru the "17Oct NZ front" in a weakened state at 25S on 19Oct and then
have SE winds on the beam for the rest of the trip to NZ -between low
near south of Niue and High in Tasman Sea, reaching Opua in light winds.
But this scenario may well change so you'd need an update before
departing.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 issued 11 Oct 2009

WEATHERGRAM
YOTREPS
Issued 11 October 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Vanuatu Quake--- this was a sideways shake so didn't toss the sea around
too much. Phew.

Palolo (or Balolo in Fiji): These worms rise out of the coral reefs for
a spawn-fest in the waning moon of Oct and Nov (around now), that's if
they haven't been upset by recent events. Anyway ask the locals,
something to do while waiting for a good voyage south,

Northwest pacific cyclone season - because the names used tin that
region cover several language with different scripts they don't go
alphabetically in the English alphabet after all. Thanks to those who
picked me up on my surprise at the jump from KETSANA to PARMAR/MELOR
last week.

MELOR was a real super cyclone for a while and managed to mostly miss
Guam, then smashed into south-eastern Japan, killing 5 and injuring
around 100.

In the South Pacific the Convergence Zone SPCZ has split into two, with
one branch from around Solomons to near Fiji, and another branch from
Tokelau across Northern cooks and touching between central French
Polynesia and Marquesas-a rare northeastern position for the SPCZ.

I think the western branch will move onto Tonga around mid week, and a
Low may form between Tonga and Niue on 14 Oct then move southeast and
deepen as it feeds off an upper jet stream. SO that may keep yachts in
Tonga while yet.

There has been an equatorial westerly during the last week between
Solomons and Micronesia, and GFS model is trying to produce a Low over
the Solomons area out of this later this week... but EC model doesn't.
In this case I'm inclined to agree with the EC.

Winds in the northern Coral Sea were strong last week but should relax
over next few days as a trough crosses the Tasman. They are likely to
get strong again
For 17 to 24 Oct as another High crosses the Tasman and this strong wind
zone is likely to affect New Caledonia from 18 to 22 or 23 Oct, so see
if that times in with your plans around there.


TONGA to NZ/ CROSSING THE SUBTROPICS
As said before- a weak part of SPCZ should visit south Tonga around
12-13 Oct and a low may form on this near Niue on 14 Oct. If you are
already at Minerva you may miss this, or perhaps can see it overhead
tonight.

In tandem with this, the HIGH over Tasman Sea today already pokes a
tongue of ridge towards NE of North Island and should travel east along
this axis maintaining a reasonable subtropical ridge between Tonga and
NZ, at 30S anyway, until 17 Oct. Although this is a nice enough ridge
to sail across the subtropics with, the problem is timing - it will get
you to NZ just when the next big trough arrives, frontal zone around 17
oct followed by a couple of days of SW to S winds. Either avoid or work
out a coping path.

BTW this trough is likely to breed a 988 Low over Tasmania in Tuesday,
avoid. Its first front should cross NZ on Wed 14 Oct and may be
somewhat thundery, announcing the return to spring over NZ after 3
winter-like lows.

Next HIGH from Australian bight should cross New South Wales on 17-18
Oct and Tasman on 19-21 Oct. So there is a possible window: a yacht
capable of up to 6 knots could possibly depart Vavau around 14 Oct, go
thru the "17Oct NZ front" in a weakened state at 25S on 19Oct and then
have SE winds on the beam for the rest of the trip to NZ -between low
near south of Niue and High in Tasman Sea, reaching Opua in light winds.
But this scenario may well change so you'd need an update before
departing.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

27 September 2009

BOBGRAM7 issued 25 Sep 2009

WEATHERGRAM
YOTREPS
Issued 27 September 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Well, the days are now longer than the nights and soon the annual
migration from tropics to NZ/OZ will be upon us, analysis paralysis will
be returning to the Minerva virtual yacht club. At this stage you've
probably heard that El Nino is in the equatorial Pacific Ocean, well
that's true but it isn't yet manifest in the atmospheric weather
patterns. This is expected to gradually become noticeable over the next
few months, as an equator-wards shift of our favourite weather zone: The
SPCZ, the subtropical ridge and the roaring 40s.
Since this is the season when the subtropical ridge normally shifts
southwards, maybe the resultant kerfuffle will appear to be just a
continuation of the current pattern.

Anyway those of you heading for NZ or Aus in yachts that average around
150 mpd or less are reminded that fronts and troughs cross the Tasman
Sea /NZ area around once every 4 days or so, thus your voyage is likely
to encounter a front. Normally the bets latitude to do this is around
30S--- sort of a mid-way rite of passage, and at that latitude fronts
are normally at their weakest, plus, if you time in rightly, it will
allow you to make landfall "between fronts" and that's a good idea.

TROPICS/SUBTROPICS
Cyclonic conditions are raging in Philippines and NW Pacific at present
and this extra convection extends across the equator to just north of
Solomons to Tuvalu, the weakens a little in a South Pacific Convergence
zone this stretches to between Southern Cooks and French Polynesia FP .
SPCZ is expected to take a rare excursion northwards across FP this week
- allowing, after its passage, a nice voyage westwards from Tahiti.

The northern end of a elderly mid-latitude front dumped hail into Suva
market last Tuesday-just in passing-just some cold air getting from
mid-latitudes into the tropics.

SUBTROPICAL RIDGE ZONE
Not much action expected here this week.
Today's HIGH in North Tasman Sea/New Caledonia area is expected to
weaken but remain as a zone of light winds that will migrate east along
around 20 to 30 S reaching Niue around 03 Oct UTC.

Another HIGH is expected to form in North Tasman Sea between Lord Howe
Island and 25S on 30 Oct and reach to 180 line around 4 Oct UTC. There
should be a squash zone of enhanced easterly winds along 10 to 20S to
north of this HIGH.

TASMAN SEA/ NZ AREA
Basically it is expected to be a week of two LOWS/

Low 1 is already deepening off Sydney, with strong SW winds over New
South Wales. Frontal zones associated with this low should cross NZ on
Monday, and the LOW itself, with attendant intense showers in a cols
pool, is expected to cross NZ on Wed, followed by strong westerly winds
on Thu. Avoid. Should be OK to make landfall in Northland on
Thursday-Friday-Saturday, but please check.

Second LOW is expected to form off southern New South Welsh coast on
Friday and turn into a trough as it crosses South Island on Saturday 2
Oct and North Island on Sun 4 October. Avoid, and this timing may
change so update.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

20 September 2009

BOBGRAM7issued 20 Sep 2009

WEATHERGRAM
YOTREPS
Issued 20 September 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS/SUBTROPICS
Last week's Low between NZ and Fiji was blocked form its normal exit
route to the southeast by a retrogression of a long wave ridge around NZ
--- This meant NZ had settled weather (after a strong NW last Monday)
and Fiji to Niue got a concentrated burst of rain from that blocked
trough. Yep, that's what flooded that Nadi bus station.

We have the equinox on Tuesday UTC, and finally the overhead sun will be
getting into the southern hemisphere. Around this time of year we often
get a mirror image of the ITCZ along 10S for a few weeks, and this does
seem to be forming now-at least from Solomons to Tokelau. In some years
the equinoctial convergence zone has tropical cyclone twins - one
forming on ITCZ triggering another in southern hemisphere and "out of
season". Not much is known about what triggers this pattern, but it is
something to add onto to list of possibilities to watch out for over
next few weeks


SUBTROPICAL RIDGE ZONE
HIGH cells migrating eastwards along 25/30S this week will keep the
South Pacific convergence zone off to its northern most position,
merging with that equinoctial convergence zone. One High will be on the
date line around Wednesday UTC and the next Sun/Mon 27/28 UTC. North of
these highs will be an area of enhanced trade winds, mainly at 10 to
15S. Because these periods of enhanced winds are no goof for fishing or
diving, and because all you need to time them is to watch the passing
Highs , I recommend that's what you do using the Fiji Map website at
http://www.met.gov.fj/aifs_prods/0641.html or our 7-day site at
http://www.metservice.com/public/maps/rain-forecast-7-day.html.

There's a trough between those two highs and it will be crossing Fiji
and Tonga around Friday/Sat 25/26 Sep. This brings fluky winds and
tropical showers so not the smoothest for sailing.

TASMAN SEA/ NZ AREA
It's too complicated and changeable for this bulletin. In this area
there is no blocking at present, so it's a ridge/trough/ridge/trough
pattern, but some of the troughs are building into deep LOWS in the
Tasman Sea, lapping onto NZ but not quite doing their worst there (yet).

For settled periods use the ridges--- one over NZ Tuesday UTC and next
is Friday UTC. There's a mid Tasman LOW between these systems on Thurs
UTC that models are deepening briefly to 975 hPa to west of Fiordland
travelling southeast. Avoid.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

13 September 2009

BOBGRAM7 issued 13 Sep 2009

WEATHERGRAM
YOTREPS
Issued 13 September 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.


TROPICS/SUBTROPICS
This week a MJO, which encourages extra convection near the equator, is
expected to weaken around the Solomons area. There was an interesting
tropical low that briefly formed in the Coral Sea to NW of New Caledonia
mid last week, and some of the energy of this is now wrapped up in the
LOW today between NZ and Fiji. This MJO is also in the India Ocean and
one computer model has come up today with the scenario of a Tropical Low
deepening near the Diego Garcia (near 5S 70E) in the Indian Ocean this
week. However the MJO is expected to be fading in this area by then, so
this will maybe just be a small low.

We are approaching the equinox, and that's when the sun gets overhead at
the equator. Around this time of the year a line of convergence
sometimes forms across the South Pacific along 10S-something like a
mirror image of the ITCZ... sort of an equinoctial convergence zone. We
might see this starting to form during the next week or two.

The South Pacific Convergence Zone SPCZ has been mainly located from
Solomons to Wallis/Futuna in the past week, and I expect its eastern
edge to wander north towards Samoa this week, and then stretch southeast
to be active in-between the Cooks and French Polynesia.

The LOW that is today between Fiji and NZ formed as an upper wave ridge
was arriving over NZ, masking NZ a place of rising rather than falling
pressure-this has blocked that low, causing it to do a loop and knocked
it a little North. Soon it will wander east (accompanying tough is over
Fiji today and should cross Tonga on Mon/Tue 14/15 Sep) and fade with a
little of it moving south well east of New Zealand.

A new trough is expected to form over Fiji and Tonga on Thu/Fri 17/18
Sep and then, on sat 19, deepen into a low near 30S 170W, to south of
Niue, and then wander off to southeast. People in Tonga looking to
sail early to NZ should wait for that trough to move off on Sat 19,
however there is a day between troughs-wed 16 Sep-which may be an OK day
to depart.

SUBTROPICAL RIDGE/ TASMAN SEA/ NZ AREA
HIGH crossing Bass Strait on 14 Sep is expected to slowdown as it
approaches NZ, should be over North island on Thu /Fri 17/18 Sep, and
linger to north of North Island Sat/Mon 19-21.

There is a disturbed westerly flow south of this ridge, with one front
crossing the South Island on 14 Sep, next on 16 Sep, next on 18/19 Sep,
next on 21/22 Sep. Each front should be preceded by a burst of NW winds
and followed by west/southwest winds.

HIGH near 30-40S 165W today is expected to wander slowly east along 35S
all week, and the squash zone of enhanced easterly winds on its northern
side should cross French Polynesia around Thu 17 Sep UTC. Good for
surfing but no good for diving or fishing.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

06 September 2009

BOBGRAM7 issued 6 Sep 2009

WEATHERGRAM

YOTREPS

Issued 6 September 2009  

Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

 

Special thanks from me to the Tokoroa Weather Watchers who treated me to some fine hospitality last night – that was fun, watching a dry slot move onto the North Island and chatting into the night about barometers, weather maps and severe thunderstorms.

 

TROPICS/SUBTROPICS

TC DUJUAN is wandering northeast off the Philippines this week,  and the Solomons/Micronesia area is likely to have a boost to its convection activity as a Madden Julian pulse of enhanced activity rolls in .

 

As for the South pacific – well, just as last week, the main part of the South Pacific convergence Zone SPCZ is in its northern-most position and is likely to stay put this week as well from Solomons to Tuvalu to Tokelau/Samoa, to Southern Cooks. A burst of convection is likely to visit Samoa on Monday UTC

 

Next weekend, around 12/13 Sep, tropical lows are likely to form to south of New Caledonia and Southern Cooks.  These Lows are likely to deepen into a compact centre that will then move off to the south east. Time any voyages to avoid these lows.

 

SUBTROPICAL RIDGE

A HIGH that is today over New Zealand is expected to become a blocking HIGH and stay put until Wednesdayn9 Sep, and then to move slowly along 30/35S as far as 170W by Sun 13 Sep, with an squash zone of enhanced easterly winds on its northern side in the tropics.  

Another HIGH is expected to form in the Tasman Sea on or around Sat 12 Sep, crossing NZ on 14 /15 Sep.

These Highs are steady enough to help in the timing of your voyages.

 

TASMAN/NZ AREA

A Low over Tasmania is expected to wander eastwards then off southwards over next few days.

Between the HIGHS there is a trough crossing NZ on 11/12 Sep, preceded by strong northerlies. Avoid.

 

 

The terms used are more fully explained in the METSERVICE Yacht Pack.

           More info at http://weathergram.blogspot.com

             Feedback to bob.mcdavitt@metservice.com

 

30 August 2009

BOBGRAM7 issued 30 Aug 2009

WEATHERGRAM
YOTREPS
Issued 30 August 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS/SUBTROPICS
Looks as though it is the peak of the cyclone season now in the Northern
hemisphere with activity in the western and eastern North pacific and in
the Atlantic... but I think TC Danny will weaken offshore as it heads
along the Gulf stream... maybe making landfall over Nova Scotia
something like Bill did.

As for the South pacific - well, the main part of the South Pacific
convergence Zone SPCZ remained in a northern-most position last week and
is likely to do so this week as well (this is where it liked to be in El
Nino) from Solomons to Tuvalu to Tokelau, and from there it forks with
one section along Northern cooks and French Polynesia and another
section across Southern Cooks.

There is likely to be a tropical trough forming over Fiji around wed 2
sep UTC (they had dry weather there during Hibiscus festival last week,
so this trough may bring some welcome rain). This trough is likely to
wander east, propelled along by westerly winds aloft. It should reach
Southern Cooks area by sun 6 sep UTC. Windy wet northerlies precede
this trough , and as it makes its way east wards across the tropics it
will kill the trade winds, and may even be followed by s cool dry
southerly for a few days. Time yourself around it.


SUBTROPICAL RIDGE
A HIGH that is today south of Niue is wandering east along 30S. An
associated squash zone of enhanced trade winds is today from around
Suvarov to Samoa and this squash zone will track east along the north
side of the HIGH and reach French Polynesia around Thu 3 Sep UTC and
then fade.

Next High is expected to build in the central Tasman Sea on Wed 2 Sep
UTC and cross NZ on Thursday at around 40S and then fade in the south
and retract to the normal 30S latitude.

TASMAN/NZ AREA
Unusually intense front is crossing NZ tonight, along with a companion
LOW sliding south out of the Tasman Sea.

A weaker front is expected on Tue 1 Sep, however that front is expected
to deepen into a big LOW near the dateline/40S on Thursday/Friday... and
that development, in cahoots with a HIGH in the Tasman should feed a
cold southerly flow onto eastern NZ especially on late We3d, Thu, and
early Fri.

Next front is likely on Sat 5 Sep UTC, and this front may linger when it
reaches the north Tasman Sea, waiting for a LOW to deepen in the Tasman
early next week.

So it's a week of possible weather windows for sailing in all direction
around NZ, and, after tonight's front, the strong winds should stay away
for a while (but avoid the southerlies on the Hawke's Bay coast on
Thu/Fri).


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

23 August 2009

BOBGRAM7 issued 23 Aug 2009

WEATHERGRAM
YOTREPS
Issued 23 August 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Apologies for delayed sending of this email--- 'twas a server problem

TROPICS/SUBTROPICS
We start the week with TCs Bill, Hilda and Vamco in the Atlantic, NW and
NE Pac respectively. Bill should sideswipe Nova Scotia, Hilda should
fade south of Hawaii, and Vamco should wander north.
As for the South pacific - well, the main part of the South Pacific
convergence Zone SPCZ has wandered to the northern part of its zone..
from Solomons to Samoa to Southern Cooks. There should be a burst of
activity near the Southern Cooks on Monday /Tuesday UTC, and another
between Tuvalu and Samoa /Tonga on Sunday and Mon 30/31 Aug UTC.

SUBTROPICS
The High positioned in the North Tasman Sea and covering New Caledonia
today is expected to move along 30S and fade near the date line on
Wednesday, enhancing the trade winds in the Coral Sea.
Next High is expected to be stronger and larger, and should build in
the Tasman Sea near 33S on Thursday, Cross the North Island on Friday,
and
Wander east along 33S after that reaching French Polynesian longitudes
on 1/2Sep, all the while with a squash zone of enhanced trade winds on
its northern side. As it wanders east of 140W around 2 Sep, a LOW
should form on its North-western shoulder near Niue. Avoid.

TASMAN/NZ AREA
That LOW which has been hovering off the NE of NZ last few days should
wander slowly along 30S as a multi-centred feature with one of the
centres deepening at 30S near 155W or south of French Polynesia on
Wednesday, bringing them a touch of westerly winds on Wednesday and
Thursday UTC.
A front is fading over north-western NZ this evening. Next front should
move onto SW of South Island on Tuesday and North Island on Wednesday
proceeded by northerly winds and followed by a northwest flow.
On Thursday another front should cross NZ proceeded by NW winds and
followed by westerlies. This front may well have thunderstorms.
Next front is likely to reach SW of south Island late sat and cross NZ
on Sunday, preceded by NW flow and followed by a S to SW flow. This
front is probably the best of the bunch for going north but still not
ideal.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM issued 23 Aug 2009

WEATHERGRAM

YOTREPS

Issued 23 August 2009  

Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from the patterned world of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.



TROPICS/SUBTROPICS

We start the week with TCs Bill, Hilda and Vamco in the Atlantic, NW and NE Pac respectively.   Bill should sideswipe Nova Scotia, Hilda should fade south of Hawaii, and Vamco should wander north.



As for the South pacific - well, the main part of the South Pacific convergence Zone SPCZ has wandered to the northern part of its zone.. from Solomons to Samoa to Southern Cooks.  There should be a burst of activity near the Southern Cooks on Monday /Tuesday UTC, and another between Tuvalu and Samoa /Tonga on Sunday and Mon 30/31 Aug UTC.



SUBTROPICS

The High positioned in the North Tasman Sea and covering New Caledonia today is expected to move along 30S and fade near the date line on Wednesday, enhancing the trade winds in the Coral Sea.



Next High is expected to be stronger and larger, and should build in the Tasman Sea near 33S on Thursday, Cross the North Island on Friday, and 

Wander east along 33S after that reaching French Polynesian longitudes on 1/2Sep, all the while with a squash zone of enhanced trade winds on its northern side.    As it wanders east of 140W around 2 Sep, a LOW should form on its North-western shoulder near Niue. Avoid.



TASMAN/NZ AREA



That LOW which has been hovering off the NE of NZ last few days should wander slowly along 30S as a multi-centred feature with one of the centres deepening at 30S near 155W or south of French Polynesia on Wednesday, bringing them a touch of westerly winds on Wednesday and Thursday UTC.



A front is fading over north-western NZ this evening.  Next front should move onto SW of South Island on Tuesday and North Island on Wednesday proceeded by northerly winds and followed by a northwest flow.



On Thursday another front should cross NZ proceeded by NW winds and followed by westerlies.  This front may well have thunderstorms.



Next front is likely to reach SW of south Island late sat and cross NZ on Sunday, preceded by NW flow and followed by a S to SW flow.  This front is probably the best of the bunch for going north but still not ideal.







The terms used are more fully explained in the METSERVICE Yacht Pack.

           More info at http://weathergram.blogspot.com

             Feedback to bob.mcdavitt@metservice.com

16 August 2009

BOBGRAM7 issued 16 Aug 2009

WEATHERGRAM
YOTREPS
Issued 16 August 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS/SUBTROPICS
After a few weeks of atrocious weather, it now seems to be settling down
now around South China and Philippines. In fact the coming week should
be drier than normal there, but TCs are still being produced on the
ITCZ - one near the dateline (TC MAKA) and another SE of Hawaii (TC
GUILLERMO, should go NW and get north of Hawaii) so take care there.

As for the South pacific - well, the main part of the South Pacific
convergence Zone SPCZ seems to have settled to be slightly north of
where it was a few weeks ago, and is now over Solomons to
Fiji/Wallis/Futuna to Tonga area. It isn't expected to travel much from
this placement over the next week or two, and that means some parts of
this zone will be getting real soggy. Vey likely an intensification of
activity may pulse along the SPCZ late this week, over Solomons on
Friday and reaching Tonga/Niue on Saturday /Sunday 22/23 Aug. Avoid.

There seems to be an increase in convection in the zone along 5S to 10S
from 180 to 140W. Over the next month or so the overhead sun will be
heading for the equator, and this typically causes a twinning of the
ITCZ with a mirror zone between 5 and 10S--- so maybe this mirror zone
is starting to form. I'll keep an eye on this.

SUBTROPICS
There has been some blocking but its eased now, so we are in for a
change in weather pattern.

The remains of last week's big fat high BFH are today around 1032 near
35S 160W, bringing enhanced trade winds on its northern since to between
southern French Polynesia and southern Cooks - all fading away by end of
Tues 18 Aug GMT as that high continues on its easterly migration.

Two more highs will enter our arena this week, but not as big as last
week's.

The first is already entering the North Tasman Sea and should feed a
squash zone in the northern Coral Sea until Tuesday that may briefly
stretch east to Rotuma.

The second should be larger than the first and bud off Australia and
expand across the central Tasman Sea on Wednesday, with a strong SSE
squash zone over New Caledonia and the full Coral Sea. This high is
likely then to contract northwards and become a slow-moving high that
will hug 30S and not reach 180 until end of next week /29 Aug. It
brings some reliability to the weather I suppose-and this weather
pattern is typical of El Nino.

TASMAN/NZ AREA
Between these migratory highs are lows and troughs... one is bringing a
southerly and welcome rain to eastern North Island tonight.

Next front is expected to fracture as it moves from Tasman Sea onto NZ
on Tuesday. There will be some wicked southerly winds following it, may
bring more welcome rain to eastern NZ (and snow to the mountains), and a
sling shot to anyone wanting to sail northwards.

This should be followed over NZ by a one-day-ridge on Thursday 20 and
then a disturbed westerly flow from Friday 21 to Wednesday 26 August
(avoid sailing with these), with an outlook of another one-day-ridge on
Thursday 27 Aug and then very strong NW winds at the end of next week,
bringing a warm spell that will end winter.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

08 August 2009

BOBGRAM7 issued 9 Aug 2009

WEATHERGRAM
YOTREPS
Issued 9 August 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

EL NINO UPDATE
During July the warming trend in the Pacific Equatorial Ocean exceeded
the threshold that is sufficient for this to be called the beginning of
a new El Nino episode. Since then this warming trend seems to have
stalled. As far as the weather patterns are concerned (looking
retrospectively) there hasn't been much sign of an El Nino yet. Its
normal for the atmosphere to lag behind the ocean like this. The
seasonal outlook is for some El Nino activity to show itself in the
South West Pacific during the coming spring-- Basically the weather
patterns will likely be drawn closer to the equator, with lighter trade
winds and with the South Pacific Convergence zone shifted northwards and
eastwards. It is still too early to draw much idea of the coming
cyclone season--- The overhead sun doesn't get to 10S until November,
and that's months and months away, and things can change. However,
since anxious cruisers like to worry about these things, if El Nino is
around in November then some tropical cyclones (which seem to like to
form on the SPCZ) may likely form in the Samoa to French Polynesia zone,
so that's a zone worth moving away from beforehand.

TROPICS/SUBTROPICS
There is a burst of westerly/southwesterly winds in the NW Pacific about
the Philippines, and this area will be a possible area of enhanced
convection and breeding area of lows. The ITCZ is active to southeast
of Hawaii, and anyone near there needs to stay tuned to TC FELICIA's
update-however it looks as though it may fade as it approaches Hawaii.

As for the South pacific - well, this week is not showing any El Nino
signs. The South Pacific Convergence Zone SPCZ, is lying from Papua New
Guinea to Northern Vanuatu/Rotuma, with another branch lying from Niue
to south of French Polynesia. The western branch may move south this
week and reach New Caledonia area or between New Caledonia and Fiji by
the end of this week--- helping form a low between Fiji and NZ around
13-14 August.

SUBTROPICS
A big fat High near 1040 hp over Chathams is expected to move slowly
northeast and fade this week -- that will enhance the easterly winds
along 20S from French Polynesia to Tonga.

A weak High is marching steadily along 55S to south of the Australian
Bight and looks as though it will cross the South Island on Wed/Thu
12/13 Aug and then join the BFH. Another weak high is expected to form
over southern QLD on Sat 15 August but then fade. So I hope people have
been enjoying this BFH while it has visited us, for it is unknown when
the next High will get to NZ.

TASMAN /NZ AREA
Lows are forming in the Tasman Sea, on the western shoulder of the BFH.
The BFH is such that these lows are being shunted south out of the
Tasman, but there are strong NE to N winds over NZ, between the Tasman
and the BFH.

Around Thursday or Friday the SPCZ may help form a subtropical low to
north of NZ, and by then the BFH may be sufficiently off to the east,
so that this low can run southwards right across the North Island on
Friday Saturday Sunday. Avoid.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

01 August 2009

BOBGRAM7 issued 2 August 2009

WEATHERGRAM
YOTREPS
Issued 2 August 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS/SUBTROPICS
The South Pacific Convergence Zone reformed last week at the northern
extent of its range - across Solomons/Tuvalu to Samoa, and then east
southeastwards across French Polynesia FP .

This week the SPCZ is likely to drift southwards as a new Madden Julian
Oscillation (boost of tropical convection) advances into the western
Pacific from Australia. By the end of this week it should stretch
across the Coral Sea towards the Loyalty Islands area/maybe New
Caledonia and then southeastwards towards Kermadecs. Another branch is
likely to stretch from Northern Tonga to southern parts of French
Polynesia.

A tale of two lows; At the south end of each branch of the SPCZ a low
is likely to form this week, disrupting the otherwise steady trade wind
flow. The Low that is forecast to form near 20S 140W on Thursday 6 Aug
UTC (call it L1) should move southeast and deepen below 10000, and is
likely to kill the winds over the main part of FP in the process.

The low that is likely to form near New Caledonia or the Loyalty Islands
on or around Sat 8 Aug UTC, call it L2, is at this stage forecast to
deepen to around 1006 and become complex as it moves south towards North
island early next week.

Avoid these lows, or maybe use them as clockwise wind swings.

During the coming week a weak trough is likely to remain
quasi-stationary to north of 30S between NZ and Fiji: Its eastern side
is wet with northerly winds, and its western side is relatively dry with
S to SE winds.

SUBTROPICS
The remains of last weeks big fat high BFH is quasi-stationary near 35S
115 to 145W, enhancing the trade winds between 20 and 25S on its
northern side. However, its western flank is expected to fade when L1
forms over southern FP around 6 Aug. Avoid the squash zone between the
high and L1.

A weak high cell is expected to chug along 32-35S from east of NZ on Mon
3 Aug to 170W on Thu 6 Aug and there fade.

A new high cell is likely to form in the Tasman Sea on Thu 6 Aug and to
cross central NZ on Fri 7 Aug and then build to over 1030 east of NZ,
near 35-40S 160-170W, this weekend and early next week. Beware the
squash zone between it and L2--- these strong NE winds make sailing from
NZ to Tonga a bad idea from 8 to 12 Aug.

TASMAN /NZ AREA
A long-wave trough LWT is stuck over the Southern Bight and its
ridge-buddy is stuck over 180. The LWT is generating fronts and tossing
them across the Tasman at the rate of around one every other day.

These fronts do not really have attached lows associated with them and
vary in intensity and are generally decaying as they cross NZ, but have
guts in them when the reach our SW end. There is one crossing the
North Island this evening (Sunday 2 Aug), next one is due Tuesday and
then a weak one on Thursday and another on Saturday. These fronts are
preceded by NW flows that concentrate the rain on the western slopes of
the main divide and bring Foehn warming downwind into the rain-shadow.
Yes, this is typical of an El Nino.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

25 July 2009

BOBGRAM7 issued 26 July 2009

WEATHERGRAM
YOTREPS
Issued 26 July 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS/SUBTROPICS
The South Pacific Convergence Zone is gradually reassembling itself
after another quiet week last week. Convection has been active about
northern Papua New Guinea and over the Solomons... and occasional
convection is appearing around Tuvalu and Tokelau, and around Southern
Cooks. Fiji had a dry week last week.

This week, the SPCZ is expected to start re-building itself in the
northern Coral Sea and extend towards New Caledonia /Vanuatu.

Much of the South west Pacific will have fairly steady trade winds this
week, but there will be some variations.

The tropical extension of a mid-latitude trough is affecting Southern
Cooks over next few days (27 to 29 July UTC), and this is expected to
affect southern Island of French Polynesia from 30 July to 1 Aug.

As for those sailing from Galapagos to Marquesas: the next week or two
is looking OK, with east to southeast winds maintained OK as Highs
travels east along 30S from 140W to 100W... These winds may weaken for a
few days around 2 Aug as that trough (between Highs) travels east along
30S.

SUBTROPICS
The subtropics east of 180 is currently dominated by a large low that
formed near Kermadecs after last few days. This low is forecast to move
east along 35S sucking away some of the force in the trade winds
further north as it wings along this path - south of Niue on 26-27 Jul,
and south of Cooks on 27-29 July.

Following this Low a new HIGH is forecast to form east of Chathams by 29
July (from the ridge that is moving east across NZ this weekend). This
HIGH should build and travel NE to 30S 140W by 2 Aug... forming a squash
zone of enhanced trade winds over French Polynesia

TASMAN /NZ AREA
Trough is crossing the Tasman Sea and is forecast to cross NZ on
Wednesday, followed by a disturbed westerly flow... that will be SW on
Thursday, a front over the South Island on Friday, westerly on Saturday,
and northwesterly by Sunday.

This disturbed westerly flow is expected to bring heavy rain to the
Southern Alps, and dry mild weather to the eastern South Island. A new
subtropical High cell may form between Lord Howe and Norfolk Island on
1-2 August, bringing another settled weekend (like this one has been) to
North Island.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

18 July 2009

BOBGRAM7 issued 19 July 2009

WEATHERGRAM
YOTREPS
Issued 19 July 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS/SUBTROPICS
The South Pacific Convergence Zone is gradually reassembling itself
after a quiet week last week. Convection has been active about
northern Papua New Guinea and over the Solomons... and also in an
unusual band between 2 and 6S from 140 to 160W - this could be extra
convection triggered off by warm seas near the equator. There is
currently an amazing blob of convection near EQ q65 to 170E, with
squally gales and westerly winds on its northern side/easterly winds on
its southern side---a sign of El Nino kicking in - and is more likely to
go north rather than south.

El Nino is pretty much here now as far as the equatorial Pacific ocean
temperatures are concerned, but, so far, just a few signs in the
atmosphere. One of these is a distinct dropping off in wind speed in
the trade winds between 100to 120W fro those sailing from Galapagos to
Marquesas to think about.

This week, the SPCZ is expected to start re-building itself, and extend
from Solomons to Tuvalu and Tokelau maybe to Rotuma and Futuna.

There is a weak trough moving east across Fiji on Monday and Tonga on
Tuesday --- the tropical extension of a front that crossed Northland on
Friday and Gisborne on Saturday. This trough is forecast to develop a
Low near 25S on Tuesday, as it crosses Niue. That Low should be taken by
a jetstream quickly S=southeastwards and may well bomb on Wednesday near
30S 160E as its trough crosses Southern Cooks. Standby for some squalls
from this passing trough.


SUBTROPICS
A subtropical HIGH around 1024 hPa has formed in west Tasman Sea and is
about to go east along to 25 to 30S zone. There will be a bunching of
isobars on its northern side as it travels--- a squash zone ----for
Coral Sea and Vanuatu on Monday and Tuesday, for Fiji from Tuesday to
Thursday, for Samoa from Wednesday to Saturday, and for Southern Coos
from Thursday to Saturday. These are good days for windsurfing, not so
good for fishing.

TASMAN /NZ AREA
That High travelling east along 25/30S will bring a touch of spring-like
weather to NZ for the start of this week, but more cold air from the SW
will likely remind us of winter again from mid to late week.

For Monday and Tuesday, west to NW winds - shower sin the west and
milder dryness in the east. Ah, I can see daisies in the lawn at last.

On Wednesday a southerly is forecast to rip across Tasmania and cold air
entering the south Tasman should mould a low. This Low is forecast to
move northeastwards across North Island on Thursday and Friday, and then
(over the weekend as it moves off to east of NZ) it may deepen and
re-curve to the E then ESE as it goes past 180. It is followed by a
cold SE wind change that will linger near Gisborne on Saturday and
Sunday.

The following HIGH is NOT at 25S - it is more likely to be at 45S (so
breaking up the spring-like pattern for a while). It should bring a
period of light winds to Tasmania on Thursday and Friday, to South
Island on Saturday and Sunday, and to North Island on Monday 27th.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

11 July 2009

BOBGRAM7 issued 12 July 2009

WEATHERGRAM
YOTREPS
Issued 12 July 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS/SUBTROPICS
Rather than a South Pacific Convergence Zone this week, there is, at
present, a straightforward tropical trough almost-north-to-south and
moving east across the South Pacific---it passed over New Caledonia last
Thursday/Friday and is over Fiji today - and should be over Tonga on
Monday, Niue on Tuesday, Southern Cooks on Wednesday and, in a weaker
and more drawn-out state, may cross the southern Islands of French
Polynesia FP on Thursday and Friday UTC.

This trough is forecast to be followed by a HIGH, zipping east along 30S
this week - the High should be south of New Caledonia on Monday, reach
180 on Tuesday, and be south of FP on Saturday.

As the trough approaches a place, winds turn northerly and become fitful
and the weather becomes squally; and following the trough are southerly
winds and clearing weather.

This trough is only moving along places south of 15S---further north are
healthy trade winds over the entire Southwest pacific. But these trade
winds weaken when the trough travels by to the south, and then
strengthen when the following high zips by to the south.

Another tropical trough is expected to form over the Coral
Sea/Vanuatu/New Caledonia area on Thursday and maybe reach Fiji on
Saturday and Tonga on Sunday 19 July. There seems to be a rhythm here,
but the following high is likely to behave differently for this week's
high, so don't get too settled into this pattern.

TASMAN /NZ AREA
Not much rhythm in the Tasman.

This weekend's low was formed by interaction of a jet stream and a
tropical trough - it brought damaging wind/rain to Northland last night,
but a dense surface-hugging layer downwind of the Coromandels stopped
the southeast gales from reaching sea-level at Auckland harbour.

Next front should roll in from the south, reaching South Island late of
Tuesday and eastern North Island on Wednesday.

Then a trough should linger over the North Island on Thursday. On
Friday, this is likely to join forces with that tropical trough already
mentioned over New Caledonia/Vanuatu and form a new LOW to north of NZ.
This new LOW should swing ESE past northern NZ on Late Friday/Saturday,
deepening as it goes... Avoid.

New High is likely to cross south of Tasmania on Thursday/Friday and
move into Tasman Sea on 18/19 July weekend, strengthening the trade
winds in the Coral Sea. Avoid the squash zone between this high and the
low over northern NZ.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

04 July 2009

BOBGRAM7 issued 5 July 2009

WEATHERGRAM
YOTREPS
Issued 05 July 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS/SUBTROPICS
The South Pacific Convergence Zone SPCZ has been active at the northern
extend of its range between 10 and 15S especially between Papua New
Guinea and Solomons, between Tuvalu and Tokelau, and between Tuamotu and
Marquesas.

Having the SPCZ slightly further north than normal is a sign consistent
with EL NINO, and indeed the sea surface and sub-surface temperatures
near Galapagos have been on a warming trend for the past month or so and
if this continues the tropical pacific ocean will be into an El Nino
pattern by August. The Atmosphere is lagging behind the ocean, but
maybe this northern SPCZ is a sign of things to come. The Monsoon is
about a week late over inland India and delivering around 75% of its
normal rain - these sort of events are usually associated with an El
Nino, but it is not possible to jump to conclusions yet. There has been
a noticeable DROP in speed in the easterly winds between Galapagos and
Marquesas over the last week or so, and this trend is expected to
continue.

Anyway the SPCZ is, this coming week, expected to drift SOUTH in the
northeastern Coral Sea, and spread into the region between Vanuatu and
Fiji.
According to the EC model a trough or LOW may form around New Caledonia
on Friday 10 July and then wander southeastwards across the Kermadecs
area on the weekend of 11-12 July. Keep a watch on this.


SUBTROPICAL RIDGE
Weak ridge near 20S in the French Polynesian longitudes is expected to
fade away by Wednesday.

The westerly flow that dominated between Lord Howe and Kermadecs last
week is starting to ease now - this zone with have a subtropical ridge
on 7 July and then the trade winds will shift southwards.

The HIGH in the Australia Bight is expected to finally cross the Tasman
Sea on Wednesday 8 July and NZ on Thu/Fri 9/10 July. Avoid the squash
zone that will form sandwiched between the northern side of this HIGH
and that trough forming over New Caledonia (8-13 July).

TASMAN /NZ AREA
It has been unsettled over NZ lately, with occluded conditions bringing
snow to the south and cold pools bringing thundery showers to the north.

Forecast maps have one more trough/Low to cross the northern areas on or
around early Wednesday followed by a final burst of southerly showers,
and then that should be the end of this period of unsettled weather, and
the start of a period of settled weather lasting into the first weekend
of the School holidays (ENJOY) but there may be lingering southerly cold
rain/snow on the Gisborne mountains on Thursday/Friday.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

28 June 2009

BOBGRAM7 issued 28 June 2009

WEATHERGRAM
YOTREPS
Issued 28 June 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS/SUBTROPICS
The South Pacific Convergence Zone SPCZ stretches across the South
pacific in two main bands ... one is a continuation of the northward
moving band which has been around for a few weeks and was mainly
stretching form Solomons to Tuvalu to Tokelau to Northern cooks this
wee. Another band has been forming from around Rotuma to Samoa. The
recent activity over New Caledonia and Loyalty Island sis due to an
incoming trough that mixes the tropics with the subtropics and mid
latitudes, and isn't part of the SPCZ.

During the next week these two branches of the SPCZ are likely to merge
into once band from Solomons to Tuvalu to Tokelau, with a side branch
extending south to Fiji. According to some models Fiji is likely to
bear the brunt of some accumulated high rainfall by early next week.
Prepare.

The Galapagos to Marquesas route is all quiet now, but easterly winds to
Marquesas are less than normal and this trend may continue, yuck.

SUBTROPICAL RIDGE
Last weeks high has turned into a sausage along 30S between 130 and
170W, and this is expected to pull out further east and wander to 25S
this week, ending over south-eastern Islands of French Polynesia. Its
associated squash zone of enhanced trade should also move north and
reach Marquesas and extend as far as 90W - so those on the Galapagos to
Marquesas voyage should have a good week if the get south of 5S. What
with the warming winds in that area, it will be wise to take these winds
while they are there, for the outlook is that they will not last.

Subtropical ridge is going thru a weak period this week in the Tasman
Sea. This allows sub-polar ridges to form instead--- that HIGH
currently over Campbell Island area is expected to head for the Chathams
by Tuesday and then fade as another High cell to the south buds off the
ice shelf - this is likely to feed chilling southeasterlies onto
southern NZ on the 4-5 July weekend.

Next subtropical ridge is forming in the Aussie Bight this week, it is
expected to get to Tasmania around 7 July and NZ around 10-11 July.

TASMAN /NZ AREA
So this week is going to be a troughy week in the Tasman Sea/NZ area.

First Low formed between Lord Howe and Norfolk Islands today, on cue,
and its front and easterly-wind squash zone is over central NZ. Low is
forecast to move east along 35S, crossing northland on Monday. Wind and
rain over central NZ should ease by Wednesday as this low goes away.
Avoid.

Second Low is forecast to deepen over Tasmania on Thu/Fri and then cross
the Tasman Sea /Central NZ on Sat/Sun 4-5 July - bringing heavy swells
to western North Island and followed by chilling SE then S and SW winds.
Avoid.

Associated front comes first and should cross Tasman Sea/NZ on Wed/Thu
preceded by a period of strong NW winds, accompanied by a burst of rain
for western areas, and followed by showery westerlies-but this front
might trigger a brief secondary low off Wairarapa on Friday.

All these troughs crossing the mid latitudes of the Tasman Sea are
making for generally westerly winds between Brisbane and New/Caledonia/
Tonga, not the other way. Use the flow, Luke.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

20 June 2009

BOBGRAM7 issued 21 June 2009 (winter solstice)

WEATHERGRAM
YOTREPS
Issued 21 June 2009
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS/SUBTROPICS
The South Pacific Convergence Zone SPCZ has recently been active in a
zone from northern Coral Sea to northern Vanuatu to Fiji - activity (not
quite the low mentioned in the last weathergram but wet enough to cause
flood warning in Fiji on Saturday) is now sliding over Wallis/Futuna
(Sunday UTC) and should slip SE and fade over Southern Cooks on Monday
UTC. This zone is now moving slowly NORTH and is likely to stall in a
zone from Solomons to Samoa from Thursday onwards.

The other weaker SPCZ zone has been between Tuvalu and Tokelau, and this
is expected to fade over ne few days.

The Galapagos to Marquesas route is all quiet now, but easterly winds to
Marquesas are less than normal and this trend may continue, yuck.

SUBTROPICAL RIDGE
A winter HIGH (caused by cold air) in the Tasman Sea is supported
strongly aloft by a planetary wave and a medium wave, so will be slow to
change this week. Its southern parts decay fastest and this causes an
apparent northeast displacement of the system across North Island on
Wednesday. Then there should be a steady eastwards movement of the HIGH
"sausage" along 30S.

Winter Highs bring frost and, as they fade, fog.

On the northern side of this is a squash zone of enhanced trade winds.
This currently stretches all the way from southern Tonga to Lord Howe
Island and should move east with the HIGH and be from French Polynesia
to Fiji on Sat 27 June. Avoid.

NZ and TASMAN SEA
In the western shoulder of the HIGH there will be a series of troughs
and Lows. First LOW is likely to form east of Tasmania on Tuesday with
a trough crossing Lord Howe on Wednesday, and weaken over NZ on Friday.
A new low is likely to form between Lord Howe and New Caledonia on
Friday /Saturday and MAY deepen quickly as it moves towards central NZ
on Sunday and Monday, making for a strong wet NE flow over Northland
this weekend for that start of the NOUMEA 2009 yacht race. And then
another trough is likely to cross New Caledonia on Monday/Tuesday 29/30
June. All worth avoiding.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

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