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

27 December 2008

BOBGRAM7 issued 28 Dec 2008

WEATHERGRAM
YOTREPS
Issued 28 Dec 2008
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
TC BILLY went offshore of Northwest Australia and deepened as it went
west into the Indian Ocean, and is now weakening away.

The South West Pacific convergence zone SPCZ has been mainly active from
Solomons to Vanuatu to midway between New Caledonia and Fiji. There has
been a side branch from around Samoa to between the Northern and
Southern Cooks. This week it looks to me that the main branch will
rebuild between Solomons and Tuvalu, and things will quieten down for a
few days over Vanuatu, but return next Sunday 4 Jan to a similar pattern
that is there today 28 Dec.

There is a Madden Julian Oscillation MJO (a boost of convection)
wandering from North Australia into the Coral Sea. This has brought
westerly winds to NW Australia, and there were a few periods of westerly
winds in the past few weeks over the Marshall Islands/Majuro, some
coinciding with high tides and causing sea flooding.

This week it seems that the winds in the Coral Sea may be light and
variable-there is a slow build up in the SPCZ and it should start
forming low pressure centres in the Coral Sea between 3 and 10 January.
Avoid the Coral Sea and its surrounds then.


SUBTROPICAL RIDGE
HIGH1 east of NZ is wandering away to the east along 40S.

A new High2 is forecast to form just northeast of NZ on Thursday 1 Jan
Tasman Sea. It may then move southeast (an unusual track for a high)
allowing a low to form on its northeastern shoulder near 35S 144W around
Sun 4 Jan, with a squash zone of enhanced winds between high and low.

HIGH3 moving into the Australian Bight is expected to cross there on Wed
and Thursday then to ridge across Tasmania and the central Tasman Sea,
reaching NZ on Saturday 3 Jan, where it may stall for a few days,
bringing high summer: settled weather for holiday makers and hay makers.

TASMAN SEA/NZ
Northwesterly flow over NZ on Tuesday and Wednesday as High1 moves
away--- showery in the west but warm and dry in the east. This
culminates in a trough crossing NZ on Thursday and Friday, damping some
New Year BBQs. Then settled weather for a while with the arrival of
High3, but there may be a low to north of NZ on Sun 4 to Mon 5 Jan much
like now Sun 28 to Mon 29 Dec, with easterly winds and onshore swells
for eastern Northland.

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 December 2008

BOBGRAM7 issued 21 Dec 2008

WEATHERGRAM
YOTREPS
Issued 21 Dec 2008
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.

On this the eve of the solstice, I wish seasonal greetings and glad
tidings to all of good cheer.

TROPICS
As forecast in last week's weather gram, TC BILLY formed northwest of
Darwin early last week and wandered southwest to west, making it onshore
near Wyndham on Friday /Saturday where it wound down. Those of you
with good Internet access can view it at
http://www.youtube.com/watch?v=oHQ48t50cTA. BILLY is expected to move
offshore and wind up to cyclone strength again, well offshore, peaking
Tuesday to Thursday this week then fading away.

BILLY formed as a Madden Julian Oscillation MJO wandered by across north
Australia. A MJO is a pulse of extra activity that wanders eastwards.
This MJO helped start the wet season in northern Australia and brought
them a humid NW flow. Equatorial westerlies have arrived over Papua New
Guinea and may penetrate eastwards towards Nauru for Christmas.

The MJO is expected to have peak impact over the Coral Sea between now
and Tuesday/Wednesday. There is a trough from northern Coral Sea across
Vanuatu to east of NZ North Island. The NOGAPS model output shows the
possibility of a low forming in north Coral Sea around Tuesday and
wandering off to the southwest. GFS, NOGAPS, UK and EC outputs all have
a low deepening to north of NZ on Monday and crossing close to East
Coast of North Island on Tuesday then whizzing off to the southeast.
That's about all we seem to be getting out of this MJO. After this it
should be quieter for a few weeks.

South Pacific Convergence Zone SPCZ is mainly extending from east of
Solomons across Tuvalu and Samoa and then to the southeast. It was very
active last week between Niue and Southern Cooks.

Not much expected elsewhere in South Pacific tropics, mainly weak NE
winds on eastern side of SPCZ and weak variable winds to west and south
of SPCZ; southeasterly between New Caledonia and Australia.

SUBTROPICAL RIDGE
HIGH in Tasman Sea on Monday is ridging eastwards towards central NZ,
and will be there on Thursday, Christmas Day, but may split into a
northern and a southern part. Then it should reform east of NZ along
dateline on Friday, Boxing day, and wander east along 40S. There will
be a good zone of enhanced trade winds on the north side of this HIGH
between 20 and 25S. This HIGH is likely to be followed by a week or so
of troughy weather, so kiwi should make hay whilst the solstice sun
shines.

TASMAN SEA/NZ
I've already mentioned the low from the north on Tuesday 23 Dec,
clearing Christmas Eve. Avoid. That should bring the last rain before
Christmas and then the outlook is for a generally dry period, albeit
occasionally cloudy, from Thursday to Sunday. Then, from 29 Dec, a
moist warm northerly flow is likely.

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 December 2008

BOBGRAM7 issued 14 Dec 2008

WEATHERGRAM
YOTREPS
Issued 14 Dec 2008
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
Near equatorial westerly winds are starting to appear in Timor Sea,
indicating a pulse of activity in the Inter Tropical Convergence Zone
ITCZ. EC model is keen to trigger a tropical cyclone out of this well
west of Darwin on 19 Dec taking it inland and killing it by 22 Dec.
Other models are not so sure, so chances at this stage are less than
50%. This pulse of activity is called a Madden Julian Oscillation MJO
and is likely to reach Coral Sea between Christmas and New Year
increasing chances then of development in our part of the world. Ah
well, most tropical sailors are ashore then.

South Pacific Convergence Zone SPCZ went south last week, and a small
development between Vanuatu and Fiji took much of the activity in the
SPCZ off to the SE. SPCZ is now lurking from Solomons to Tuvalu to
Wallis/Futuna/Samoa to between Niue and Southern Cooks. Forecast is for
SPCZ to drift south again late this week and for another small low or
trough to form (again) between Vanuatu and Fiji on 20 Dec and to move
southeast on 21/22Dec with a strengthening squash zone on its southern
side --- between the trough and a High over NZ.

Not much expected elsewhere in South Pacific tropics, mainly weak NE
winds on eastern side of SPCZ and weak variable winds to west and south
of SPCZ gradually becoming southeasterly.

SUBTROPICAL RIDGE
On 16 Dec a small High may bud off eastern Australia into Tasman Sea,
and then wander east along 30S until it fades away south of French
Polynesia on 21 Dec.

More intense High is likely to bud off eastern Australia/Tasmania into
Tasman Sea at 35S on 19 Dec, and cross NZ 21/22 Dec, and maybe reform a
new centre over Chatham Islands on 23 Dec, that might linger there 24-27
Dec. Happy Christmas Chatham Islanders!

TASMAN SEA/NZ
The remains of that large Low that moved off Australia over the weekend
are expected to weaken somewhat as they cross NZ on 15-16 Dec, followed
by cool SW flow on 17-18 Dec. New low is forecast to form on a front in
the Tasman Sea on 18 Dec and cross NZ of 19 Dec, followed by a S/SW flow
on 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

07 December 2008

BOBGRAM7 ISSUED 7 Dec 2008

WEATHERGRAM
YOTREPS
Issued 7 Dec 2008
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 below are given in UTC unless otherwise stated.

TROPICS
Last week saw the formation of two tropical depressions in the Northern
and Southern Cooks, and there is today a gale force squash zone on the
south side of TD02F near 25S 169W ....avoid...all this is moving off to
the south. The northern and southern Cooks had the majority share of
last week's rain from TD01 and 02.
TD02 will continue to peel off to the south and a lovely easterly swell
from its squash zone should reach eastern North Island areas on Tuesday
and Wednesday to the delight of surfers.

South Pacific Convergence Zone SPCZ is slowly building in strength along
a zone from Solomons to Tuvalu to Tokelau/Samoa to the Niue/Southern
Cooks area.
This zone is expected to drift south this week, and a new TD ... worth
avoiding... should form near Tuvalu on Tuesday and travel south between
Vanuatu and Fiji on Wednesday and Thursday then SE to the SE of Fiji on
Friday and Saturday, triggering further lows to form like pearls on a
necklace along a mid-latitude trough south of Tonga during the 13-14
weekend. The S/SE wind and SE swell on the western side of this trough
may affect eastern North island on 13 Dec, ah well they need the rain so
that's all good.

Not much expected elsewhere in South Pacific tropics, mainly weak SE
winds to west of SPCZ and NE winds on its eastern side.

SUBTROPICS
Subtropical ridge is hanging in there around 30S.

TASMAN SEA/NZ
A procession of troughs with fronts is set to cross NZ: on Mon-Tues 8/9
Dec, Thurs-Fri 11/12 Dec and Mon-Tues 15/16 Dec. There is a tendency
for small lows to come and go on these fronts, thus focusing wind and
rain here and there.

The Highs between these troughs are brief and weak, crossing the Tasman
Sea along 35S to 30S on 8-9 Dec, 11-12, and 16+ Dec --- these tracks and
the cool southerly flows following the troughs suggest a slight swing to
El Nino for the Tasman in the seasonal weather Jazz... but it'll only
last a week or two.

HONOURABLE MENTION OF AUSTRALIA THIS WEEK:
The biggest Low in our part of the planet is forecast to cross South
Australia on Thu 11 Dec, Victoria on Friday 12, and the Tasmania/New
South Wales Area on Sat 13. 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

29 November 2008

BOBGRAM7 issued 30 Nov 2008

WEATHERGRAM
YOTREPS
Issued 30 Nov 2008
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 below are given in UTC unless otherwise stated.

TROPICS
South Pacific Convergence Zone SPCZ has had a quiet time recently---
some strong convection near Marquesas and with an upper trough crossing
Tonga, but otherwise quiet.

SPCZ is likely to be active in the zone from Northern Cooks to
in-between Marquesas and the main part of French Polynesia and to move
south this week.

Indications are that the SPCZ may slowly pick up in activity between
Solomons and Fiji during the coming week.

In particular a tropical Low with slack winds near its centre is likely
to form over Northern Cooks on 1-2 Dec and then drift west and south,
crossing Niue and Tonga on 3-4-5 December and then maybe deepen over
Kermadecs on 6-7 Dec. Slack winds near the centre but there should be a
squash zone of enhanced easterly winds on the south side of this low---
worth avoiding--- this squash zone is expected to reach its peak near
Kermadecs/Minerva between 5 and 8 Dec.

Not much expected on western side of this low, but be on squall watch
when on its eastern side

SUBTROPICS
Upper air flow around the planet has set up long roller coasters that
are encouraging higher than normal pressures in the subtropics between
120 and 180 W and lower than normal pressures in the Tasman Sea area.

TASMAN SEA/NZ

Fronts and lows are growing well when crossing the Tasman Sea, then
fading as they cross NZ.

On Mon 1 Dec a Low should cross the South Island, followed by a westerly
flow on Tuesday.

On Thursday a front should cross Tasman Sea/NZ, proceeded by a NW on
Wednesday, and then followed by a SW flow and a brief ridge on Fri.

A similar pattern repeats on 6-7-8 Dec, but with a bigger ridge.

So it is a bit like a trampoline in the Tasman this week, try and jump
in rhythm with the 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

22 November 2008

BOBGRAM7 issued 23 Nov 2008

WEATHERGRAM
YOTREPS
Issued 23 Nov 2008
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 below are given in UTC unless otherwise stated.

Well, the troughs in the Hot Aussie interior DID make their stormy way
across Brisbane early last week and have formed a front and Low in mid
Tasman Sea.
The HIGH that crossed NZ has formed a reliable wind at last for yachts
heading from Tonga to NZ and it arrive on Wed 19 as picked in the last
Weathergram. Good to sea the weather unravel according to plan.

TROPICS
The trough moving from central Aussie to central Tasman Sea has turned
the winds in the Coral Sea to a NW flow. It will take all week for the
trade winds to return there. And maybe that's it for the strong trade
winds that have been bothering the Coral Sea over the last few months.
This transition is something look a seasonal transition... it has
allowed westerly winds and thunderstorms to reach Darwin--- the start of
the wet season perhaps. .. There is now a Madden Julian Oscillation
occurring over Indonesia along with some equatorial westerly winds
around Papua New Guinea. This should all drift east and we can expect a
boost in the activity of the South Pacific Convergence zone (SPCZ)
between around 10 to 20 Dec, increasing the chances of a Tropical
Cyclone in the South Pacific around mid December.

South Pacific convergence Zone SPCZ remains in a zone from Solomons to
Wallis/Futuna to Northern Tonga/Niue. Another smaller zone extends from
Tuvalu to Northern cooks. The computer models are indicating that the
SPCZ may shift south and west towards Fiji by the weekend of 29 to 30
Nov. Rain rather than wind, but there may be a small squash zone around
Minerva / Kermadecs late in the month.


SUBTROPICS
High is expected to linger to east of North Island until Tue 25 Nov.
Then a blocking High settles near 40S to south of French Polynesia for
the rest of the week--- there will be a squash zone of easterly winds
along 20S between French Polynesia to Niue for much of the week, good
for sailing west.

TASMAN SEA/NZ
That Tasman Low and its frontal systems is crossing NZ early in the
week, but fading as it encounters the lingering High. Nothing major for
anyone sailing to Opua, but remember to allow for the post-frontal SW
flow on Tuesday.

Next High should bud over southern Tasman Sea on Wednesday and then move
Northeast to north of NZ on Friday.

Next trough should bring a southerly buster to Sydney on Friday and
deepen rapidly into a LOW in South Tasman Sea on Sat 29 Nov then cross
southern NZ on Sun 30 Nov. Avoid.

Weather is looking settled for the CANANZ Boat Show open day at X Marina
at Westhaven in Auckland 0900-1500 Sunday 30 Dec - free entry, BBQ and
prizes, open to anyone (in Auckland) - ask for me.

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 November 2008

BOBGRAM7 issued 16 Nov 2008

WEATHERGRAM
YOTREPS
Issued 16 Nov 2008
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 below are given in UTC unless otherwise stated.

TROPICS
Some near equatorial westerly winds are appearing in the Indian Ocean
around 5 degrees north-It is too early to tell if this will produce an
east-ward moving surge of activity known as a Madden Julian Oscillation
(MJO)-might do, in which case we will need to watch the Coral Sea
closely in 4 or 5 weeks from now, just before Christmas, for possible TC
activity.

South Pacific convergence Zone SPCZ has reformed in a zone from Solomons
to Wallis/Futuna to Samoa/Northern Tonga. There is still an upper
trough lingering along 25S between NZ and Fiji/ Tonga, with light and
variable winds at sea level to north of this and a band of strong SE
winds on its southern side.

SUBTROPICS
A reliable SE wind is expected to arrive at Minerva on wed 19 Nov and at
Tongatapu on wed/thu 19/20 Nov, good for sailing with to NZ. This
sailing window is brought about by a HIGH crossing NZ on Thu 20 and then
lingering for almost a week just east of NZ. This is the best looking
window we have had so far this month for Tonga to Opua travellers.

TASMAN SEA/NZ
Front is weakening and expected to cross Northland on Monday 17 Nov,
followed by a day or so of southerly winds. Then the weather turns into
a HIGH followed by LOW, with the HIGH crossing the Tasman Sea on 17-19
Nov (good for those sailing from New Caledonia to Brisbane), NZ on Thu
20th, then lingering east of NZ along 40S maintaining a squash zone near
30S.

Large LOW is forecast to form over Victoria and New South Wales on
Wednesday (avoid) and then split into multiple centres as it crosses the
Tasman Sea and southern NZ on Thu to Monday (avoid). The W to SW winds
following the fronts of these lows should reach Northland around Mon
/Tue 24/25 Nov (these can be used for sailing, with care).

The HIGH following this Low is forecast to collapse in the Tasman Sea,
paving the way for another family of LOWS to form in the hot Aussie
interior early next week. This all means unsettled weather in the
Tasman Sea from wed 19 November for maybe 10 days.

I am in Greymouth this week attending MetSoc/hydro Soc conference. Had
scallops and whitebait, followed by a mushroomed T bone and washed down
with Monteiths this evening. Will be back checking email from Sat 22
Nov

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 November 2008

BOBGRAM7 issued 9 Nov 2008

WEATHERGRAM
YOTREPS
Issued 9 Nov 2008
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 below are given in UTC unless otherwise stated.

TROPICS
Monsoon looks less active than last week but did produce a TC MYSAK.
There is no sign of any equatorial westerlies and no sign of a Madden
Julian Oscillation so looking like it will be a few weeks, maybe more
than a month before we start seeing cyclone activity in this part of the
world. Wow, TC Paloma moving in from the south onto Cuba shows there
is plenty of energy available over there.

South Pacific convergence Zone SPCZ has cleared away from Coral Sea
during past week and is now weak from Tuvalu to Samoa to Northern Cooks.
The active thundery area which visited Fiji Wednesday and Tonga /Minerva
/Kermadecs over past few days and is now over the Niue area is really
caused by an upper trough sitting on top of the tropical easterlies.
This bunch of cold air aloft is confirmed by the hail and whirlwinds in
the showers that visited Fiji last Wednesday. And that's why the winds
have been so slack south of Fiji/Tonga and NZ last week. Anyway the
upper trough has "eaten downwards" and formed a slack surface low near
Kermadecs as picked in the last Weathergram. Yippee, it is good to see
the physics working-we had a lot of cold air flood over NZ last week and
its arrival in the subtropics threw the global weather models in a tizzy
for a few days - their grip on the real world seems to have returned
now.


SUBTROPICS
There is a slack variable flow between Fiji /Tonga and NZ with the
subtropical ridge now shifted to around 40S.
Another upper trough is likely to form another slack surface low near
Lord Howe Island on the front passing the area Sunday/Monday. This will
stall the front so that it sits between New Caledonia and Queensland for
the remainder of the week, fading away. That Low near Kermadecs has a
squash zone between it and the intense subtropical ridge that is near
40S. This squash zone is near 30S and reaches a peak on Monday,
probably worth avoiding unless you like roller coasters Between the
Kermadecs and Lord Howe Lows is a zone of light winds for much of this
week.

HEADING FOR NZ
Front in the Tasman Sea today Sunday is expected to fade over the South
Island on Monday, allowing a new HIGH to form in the central and
southern Tasman Sea on Tuesday and this crosses central NZ on Thursday.

Next front should have more penetration, getting across Northland late
16 or early 17 Nov. Avoid arriving in Opua with or just after this
front. At this stage 18 to 22 Nov are all looking OK days for making
landfall--- try and arrange to go thru this front when it is at 30S ,
say on 17-18 Nov or soon after. From those dates and your vessel speed
you can work out when it may be best to depart Fiji or Tonga or Minerva.
Looks like a breeze good enough for sailing should return to these
places around Wednesday 12 or Thursday 13 Nov, maybe - but the lights
winds on the way will mean some motoring.

I am attending to a MetService display at the Royal Show from Tue 11 to
Fri 14 inclusive, so unavailable this week. Will check email on Sat 15,
then unavailable again from Sunday 16 to Friday 21 Nov, attending a
conference in Greymouth, back on deck Sat 22 Nov. So happy sailing
while I'm away.

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

02 November 2008

BOBGRAM7 issued 2 Nov 2008

WEATHERGRAM
YOTREPS
Issued 2 Nov 2008
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 below are given in UTC unless otherwise stated.

TROPICS
Monsoon over Indonesia and Philippines is starting to drift southwards
towards the equator, but the wet season is yet to reach Darwin. There
is a Madden Julian Oscillation occurring - or, in other words, an
increase in showery activity is meandering along the Intertropical
Convergence Zone from Indonesian eastwards. This is happening mainly
along the latitude of 5 North, but I expecting an increase in activity
over Papua New Guinea/ Coral Sea area during the next few weeks - so
this could be an area to be watchful.

South Pacific convergence Zone SPCZ is in a position further south and
west than normal and has been stretching across Vanuatu to south of Fiji
to the Kermadecs area. Another branch extends along 10S from Solomons
to Tuvalu /Tokelau and occasionally visiting Northern Cooks and
Marquesas.

SUBTROPICS

The western branch of the SPCZ is clearing itself at present, but a
jetstream + tropical moisture are feeding an upper trough that has been
lingering over the Minerva /Kermadecs region. This may trigger a slack
surface low over Kermadecs on Tuesday that will move SE and fade away on
Wednesday.

--- Hey, this system will reconfigure the subtropical ridge around about
and kill the trade winds from Southern Cooks to Fiji from Tue to
Friday--- so it is a week of light winds between Tonga/Fiji and New
Zealand. OK for sailing but it will require some motoring through areas
of slack wind.


TASMAN SEA / NZ AREA
Weak ridge starts the week in the Tasman Sea.

A trough crosses the Tasman Sea on Monday and NZ on Tuesday, avoid -it
is followed by heavy swells that reach a peak in the Tasman Sea on
Thursday, avoid.

Wednesday and Thursday -- a westerly flow.

Friday: a Low is likely to cross central NZ; it may deepen over Chathams
but will be weak over northern NZ.

On Saturday a LOW is expected to deepen in the South Tasman Sea and then
weaken as it crosses the North Island followed quickly by a ridge. This
low is worth avoiding in the Tasman Sea BUT shouldn't pose much of
problem for anyone approaching Northland... in fact the northerly flow
ahead of it will help anyone arriving Sunday/Monday 9/10 Nov. Enjoy
watchfully.

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

26 October 2008

BOBGRAM7 issued 26 Oct 2008

WEATHERGRAM
YOTREPS
Issued 26 Oct 2008
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 below are given in UTC unless otherwise stated.

TROPICS

Nov to April is the period described as Cyclone season for the South
Pacific. Most Insurance companies do not pay out on any storm damage to
yachts in the South Pacific during this period, so that's why early
November triggers a migration of yachts out from Tonga and Fiji.
Climatologists looking at the coming cyclone season are expecting, on
the basis of the sea surface temperature trends, that it should be
average (8 to 10 named systems) with a slight drop in risk east of the
date line and a slight increase in risk for the Tasman Sea/NZ area.
Normally the first cyclone appears soon after equatorial westerlies
arrive over the Papua New Guinea/Solomons area... the Monsoon is active
over Indonesia but there is no sign of these westerlies, so my pick is
that the first cyclone is something like six weeks or more away.

South Pacific convergence Zone has been stationed from Papua New Guinea
across Coral Sea to Vanuatu/ New Caledonia in past week and
intermingling with a mid-latitude trough that crossed New Zealand.
Another branch has been coming and going in the Samoa area.

Not much change expected in the SPCZ this coming week, but some
activity is expected between Tuvalu and Vanuatu early this week.

SUBTROPICS

I received an email from a yacht near the dateline and 30S on Saturday
reporting 30 knot westerlies and 8 metre swells. So my weather gram
last Tuesday was worthwhile following. The trough is still lingering
over Kermadecs today and may bring some squalls to the Minerva area on
Tuesday or Wednesday.

Subtropical ridge is likely to be draped along 30/33S between 160W and
160E all this week until Sun 2 Nov. Slack winds and left over clouds
in this zone, but SE winds are likely to often be over 20 knots between
20 and 24 South, including Minerva reef.

TASMAN SEA / NZ AREA and the All Points Rally

With the annual yachting migration about to occur there is also the All
Points to Opua Rally of the Island Cruising Association, mainly from
Pangaimotu (Tonga)/Musket Cove (Fiji)/Vila (Vanuatu)/Isle des Pins (New
Caledonia) to Opua, starting 1/2/3 Nov.

There isn't much dramatic happening in the weather, but anyone leaving
Fiji/Tonga before Wednesday will likely need to go on squall watch
during Tuesday/Wednesday near 22 to 24South.

Early next week, around Monday 3 November, as a front crosses the North
Island, a small Low is likely to form on this front. This Low then
likely grows and fades when it is east of the North Island on 4 to 6
November... making for several days of SW flow over Northland.

So maybe your strategy will be to time your arrival in Opua after this
SW - or maybe sail so you take them as side-on as you can. It's hard to
tell this far out, but current indications are that the SW winds near
Opua are likely to be strongest 4-6 Nov.

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 October 2008

BOBGRAM7 SPECIAL issued 21 Oct 2008

WEATHERGRAM
YOTREPS
Issued 21 Oct 2008 EXTRA ADDITION PLEASE READ
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 below are given in UTC unless otherwise stated.

TONGA to NZ update

Computer models are now converging with their output handling the LOW
that is now forming in the Tasman Sea. It is expected to deepen as it
crosses northern NZ on Friday and east of the North Island on Saturday.
There is a high likelihood of westerly gales at 30S from about Norfolk
to Kermadecs on Sat 25th.

SO if you are trying to get to 30S by 24 Oct as I suggested in my last
Weathergram then please ABORT. If you know someone who has sailed off
please pass this on. That strategy for getting from Tonga to NZ WORKS
WITH FRONTS but it DOESN'T WORK when fronts have LOWS of this size
attached to them. Time now to return to port and await the next
window... the front associated with this low is expected to clear off
southern Tonga on Mon 27 Oct so next window may well be Tuesday 29 Oct.

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 October 2008

BOBGRAM7 issued 19 Oct 2008

WEATHERGRAM
YOTREPS
Issued 19 Oct 2008
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 below are given in UTC unless otherwise stated.

TROPICS The South pacific Convergence Zone, SPCZ, went through a period
of activation in the Coral Sea last week. This was induced by a passing
of an upper level trough and the corresponding 'blob' went over Loyalty
Islands on Friday, to south of Fiji on Saturday and is now weakening
over Minerva reef. The latest Quikscat imagery conforms a reflection of
this trough at surface level, with a zone of northerly winds and
clearing weather passing over southern Tonga today and Monday (UTC).
May be useful for Island hopping.

The SPCZ this week is expected to mainly extend from northern Coral Sea
to Vanuatu to south of Fiji and occasionally to Southern Tonga, with
another branch from Tokelau to Northern Cooks

For the Port2Port this week there is an unavoidable squash zone in the
Coral Sea, it marks is fed by a rather weak HIGH cell crossing the
Tasman Sea from 19 to 21 Oct. Another HIGH is likely to cross the Tasman
Sea from 23 to 27 oct, and its squash zone may weaken from 26 Oct as the
SPCZ goes through another period of activation.

NZ/TASMAN SEA
The main challenge this week comes from a LOW that is likely to form
near Lord Howe Island on 21 Oct. By the way, this low is expected to
form between highs in the subtropical ridge, a standard pattern. The
conflicting densities of air feeding into this low from the warm moist
north and the cooler south is not being handled well by the computer
models. The main model that you may have access to in your GRIB files
is the GFS, and it and the NOGAPS model deepen this low and take it
across the North Island on Friday, just in time for our COASTAL CLASSIC
from Auckland to Bay of Islands. The EC and Canadian models do not
deepen it so much and may track across the north of Northland, a
different outcome. At this stage the best pick is somewhere in-between
and nothing more definite can be written until the models start to
converge.

One thing that can be said about this low is that it will be forming
whilst a front, today in the South Tasman Sea, moves north across New
Zealand. That front is followed by some grunty swell from the southern
Ocean and the LOW will help enhance that swell, especially along the
western part of the Tasman Sea along the Australian coast as far north
as Brisbane to Lord Howe on Thursday, and also on the western side of
the Low as it crosses whichever part of northern NZ it does around 24
/25 Oct. Avoid this swell.


Tonga to NZ
I like the idea of taking on a front at around 30S--- they are weak at
that latitude and there plenty of ocean to play with. Fronts this time
of the year are about 5 to 7 days apart on average crossing NZ, and the
voyage, over 1000nm will take you over a week so meeting a front is
unavoidable. Doing so mid-way maximises your chances of making landfall
in NZ "between fronts". I think this is a better strategy for a
cruising yacht than attempting to make landfall in NZ as a front is
approaching (but some may prefer this).

Anyway: this week THE FRONT associated with that Tasman Low is
expected to be crossing that magic point-pretty well half-way between
Raoul Island and 30S 180- on 24 Oct. So my best idea is that you depart
from where you are in Tonga to reach that point around 24 Oct and head
sufficiently off to the west to allow for the SW winds that will follow
that front, and the SW winds that will be on the western side that that
low, and you should have a reasonable voyage. As for the swell on the
western side of that Low, you will meet it near 30 to 35S over the
weekend, but by then it will be around 3m and on the decline /long
period, so not too bad.

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 October 2008

BOBGRAM7 issued 12 Oct 2008

WEATHERGRAM
YOTREPS
Issued 12 Oct 2008
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 below are given in UTC unless otherwise stated.

October's full moon is on the 15th - good for cruising. During the
following week, induced by the spring tides a few days after that full
moon, there will be a few nights where the annual PALOLO RISING (in Fiji
the BALOLO RISING) may occur when coral worms spawn. Worth checking
out, ask the locals. And the New Moon on the 29th is marked with the
Hindu Festival of Lights - rather dark for cruising.

The annual analysis paralysis season is about to start as cruisers in
Tonga gather all their ideas together to try and pick the 'best' time to
leave for NZ. My ideas will be just part of this, and I have no ideas
beyond 24 Oct at this stage.

TROPICS The South pacific Convergence Zone, SPCZ, extends from Solomons/
Coral Sea to Wallis/Futuna to central Tonga to a LOW that has formed
south of Niue. - There is a weaker branch from Samoa to Northern Cooks.
That Low south of Niue is expected to fade where it is on Monday. The
area should remain troughy with a squash zone near 30S 150 to 170W as a
big fat high moves east of NZ and bananas-around it at 40S, 14th to 16th
Oct. Avoid this squash zone - but is should generate some useful swell
for surfers in Bay of Plenty/ Bay of Islands for 18/19 Oct (this isn't
being picked by the computers but I think it's a good possibility). The
troughy area should reforms that Low near 30S 160W on 16th as that high
moves further East, and the LOW should be captured by the next
mid-latitude trough and go off to the SE-associated trough should bother
Niue on 15 Oct and may bother Southern cooks on 16-17 oct. Take care.

SPCZ is moving south across Coral Sea and computers are picking it may
develop a trough visiting New Caledonia 15 to 17 Oct and Southern Tonga
17 to 19 Oct. Squally showers, and appears in those GRIB files as a
deceptive zone of light variable winds. Avoid.

SUBTROPICS /NZ/TASMAN SEA
One migratory HIGH is moving along 40S across NZ on 12-13 Oct and then
off to the east 14-17 Oct. Its squash zone is being focused at 30S by
that troughy region south of Niue.

Between Highs, a trough should broaden over NZ 16-18 Oct.

Next subtropical HIGH is expected to form in Tasman Sea 16 oct and move
northeast and fade over Lord Howe area 19 Oct-it is a brief one, but
good for Tasman sea sailing.

Next trough broadens over NZ area 20-24 Oct and since the next HIGH
seems likely to form in the Tasman Sea at 40S , that would suggest a
cold southerly over NZ on 23-24 Oct. Avoid.

Sailing to NZ? Try and arrange your arrival to be WITH the HIGHs
(13-15, 18-19, 24-26 Oct).

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 October 2008

BOBGRAM7 issued 5 Oct 2008

WEATHERGRAM
YOTREPS
Issued 5 Oct 2008 NZDT
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 below are given in UTC unless otherwise stated.

Addendum to those comments last week about the coming cyclone sea:
Outlook is for neither El Nino nor La Nina, so neutral territory.
Previous years in neutral territory show a REDUCED RISK of cyclones
around Northern Cooks and French Polynesia. For NZ there is an INCREASED
RISK. In-between these places a normal cyclone year may be expected,
and that included the Coral Sea/ Vanuatu area.

I'll be brief this week because it is late Sunday after a weekend of
sailing fro me.

TROPICS The South pacific Convergence Zone, SPCZ, extends from Solomons
to Tuvalu - this branch may move slowly southwards during the coming
week possibly reaching central/southern Vanuatu to Fiji by 15-17
October. Avoid. Another weaker branch of SPCZ extends from Tokelau
across Northern Cooks towards Marquesas. The northern extension of a
mid-latitude front was noticeable from Vanuatu to Fiji and thence to the
Southeast last week (even had some gale warnings), but isn't likely to
appear this week.

Southeast trade winds cover the entire South Pacific-no sign of any
westerly winds yet. Since the subtropics are well marked between 30 and
35S these trade winds are generally strongest along 20S.

SUBTROPICS
One migratory HIGH is moving along 30S, and centred south of Fiji to
French Polynesia on Monday should fade by Wednesday. Next HIGH is
likely to appear in western Tasman Sea on 9 Oct and cross the North
Island along 35S on 11-12 Oct and fade away by 14 Oct.

North of these HIGHs, there will be enhanced east to southeast winds at
20 S.

TASMAN/NZ
Front crossing NZ on Monday Tuesday 6/7 Oct is likely to also bring a
LOW crossing the South Island. Avoid. Severe westerly winds should
follow this front on Wednesday 8 Oct (avoid) followed by a easing
anticyclonic SW flow on Thu 9 to Sun 12 (OK). Spring -type 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

27 September 2008

BOBGRAM7 issued 28 Sep 2008

WEATHERGRAM
YOTREPS
Issued 28 Sep 2008 NZDT
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 below are given in UTC unless otherwise stated.

NIWA in NZ have issued their annual idea of the coming cyclone season in
the South West Pacific. It is likely to remain in neutral territory -
neither a La Nina nor an El Nino. Around the South Pacific previous
neutral cyclone seasons have given an average number of cyclones -
around 8 to 10. The coming season is likely to bring a REDUCED RISK of
cyclones around Northern cooks and French Polynesia. For NZ there is an
INCREASED RISK - by the time such systems reach NZ they are no longer
Tropical Cyclones but some still pack a punch. Memorable cyclones in NZ
such as FERGUS and DREANA have occurred in neutral years.

No sign of any tropical cyclones in the South pacific during the coming
week. There are some near equatorial westerly winds to north of Papua
New Guinea, and these may be heading for Micronesia, so take care there.


TROPICS The South pacific Convergence Zone, SPCZ, is having a brief
break over the Coral Sea but should reform there this week. There is
one branch over Fiji/Tonga at present and it is being propelled
eastwards by the upper westerly winds. It should fade on Tue/Wed UTC
from Samoa to Southern Cooks, but will likely trigger a LOW for form
southeast of the southern Cooks , near 30S 150W , on Thu/Fri/Sat.

A mid-latitude Low crossing NZ on Monday is likely to link into the
tropics on Tue forming a trough that crosses Fiji and Tonga on Wed, Niue
on Thursday and Samoa to Southern Cooks on Friday.


SUBTROPICS
A migratory HIGH is expected to arrive in the Tasman Sea on Wednesday
and then move east along 30S finally reaching 150W, south of French
Polynesia, the following Tuesday. These HIGHS enhance the SE trade
winds on their northern side as the pass by. In Fiji they are called
Bogi Walu (eight nights) because the enhanced trade winds give a week of
wet nights to Suva. Have fun riding these winds, going westwards.


TASMAN/NZ
Front crossing NZ on Monday should be followed by a strong SW flow on
Tuesday, and then a typical spring westerly flow until Friday. Next
front, preceded by strong NW winds, should cross the South Island on Sat
and ease over the North Island on Sunday.

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

21 September 2008

BOBGRAM7 issued 21 Sep 2008

WEATHERGRAM
YOTREPS
Issued 21 Sep 2008 NZST
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 below are given in UTC unless otherwise stated.

The overhead sun crosses the equator at 1544Utc on Monday 22 Sep (around
4am Tuesday in NZ) - its about a day after the usual 21st sep because of
the leap day we had this year. Around the equinox we sometimes notice a
twinning of the ITCZ with the South Pacific Convergence Zone SPCZ, and a
branch of the SPCZ intensifies along 10South from about Tuvalu /Tokelau
to Northern Cooks and sometimes to Marquesas-no sign of this yet but it
may appear.

TROPICS Easterly winds to north and southeast winds to south of the
SPCZ. The winds are strong within the SPCZ over northern parts of Coral
Sea (avoid). And the SPCZ is active from there to North of Vanuatu to
Rotuma/Wallis/Futuna to Tonga to Niue. It is expected to travel south
this week, reaching Vanuatu/Fiji on Mon/Tue then fading away on Wed/Thu.
In this southern excursion a small LOW may form in Coral Sea on Fri/Sat
then head south into Tasman Sea early next week bringing wet NE winds to
New Caledonia on Fri/Sat. There will be a squash zone on the south side
of this LOW so take care if travelling between Vanuatu/New Caledonia and
Australia.

SUBTROPICS
For those of you from the Northern Hemisphere-welcome to the South
pacific with its migratory HIGHS.

HIGH between Norfolk and Raoul on Sunday is moving slowly along 33S and
should fade east of 180 by Thu.

HIGH on Aussie Coast on Sun should travel along 35S reaching Tasman Sea
wed/Thu and Northland on Fri/Sat and tongue out a ridge along 33S to
south of French Polynesia early next week.

On the northern side of these HIGHs there will be an enhancement of the
trade winds--- mainly between 25 and 20S.


TASMAN/NZ
Between the HIGHS are troughs and fronts, but no LOWs this week. So it
is a typical spring pattern.

First front is fading over North Island Sun/Mon.

Second front should cross South Island on Tue, preceded by strong NW
flow (especially for eastern areas) and accompanied by heavy rain in
western areas. Then fade over North Island on Wed.

Third front should reach South Island on Friday and hang about the North
Island on Saturday and Sunday.

Try and plan your Northland arrival/departure dates to be on Tuesday
/Thursday -Friday; in-between days rather than frontal days.


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 2008

BOBGRAM7 issued Sunday 14 Sep 2008

WEATHERGRAM
YOTREPS
Issued 14 Sep 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

TROPICS We are now approaching the equinox -it will be on 23 Sep and
then the days in the southern Hemisphere will be longer than the nights
and soon after that I will start to give out my ideas for the coming
South pacific cyclone season. Things are still in the "non-cyclone"
season mode with trade wind easterlies over the whole area and no sign
yet of any equatorial westerlies.

South Pacific Convergence Zone SPCZ is patchy in coverage... It is
strongest about Papua New Guinea and Solomons... Another burst of
activity at times between Tokelau and Samoa, and occasionally over north
Tonga, then it sort of stretches from about Niue to Southern Cooks and
southern parts of French Polynesia. Not much change is expected in
these areas during this week.

The main thing to consider, if Island-Hopping this week, is the
subtropical trough currently crossing Fiji. Its rain band should reach
Tonga on Monday UTC and Niue on Tuesday and then fade over Southern
Cooks by Thursday. It goes eastwards even in the trade wind belt north
of 25S by virtue of the westerly winds it has about and above its
clouds. The surface easterly winds turn NE and ease as the trough
approaches , there are some squally tropical showers as the trough
crosses and then the winds fill in again as steady SE winds as the
trough moves off to the east. If you are watching this trough's
footprint by means of Grib winds do NOT be led astray but the light
winds it shows with this trough - The computers cannot resolve the
tropical squalls and each will be able to produce 30 knots in 30 minute
bursts. SO if you are intending to sail across this trough, then go on
squall watch.


SUBTROPICS /TONGA and FIJI
A LOW is developing in this trough near Kermadecs today / Sun 14 Sep /
and should wander off to the south. SW to Southerly winds on the
western side of this LOW are likely to affect Fiji and Tonga until Wed
17 Sep so best to wait for these to swing back to SE winds before
sailing west in this area.


TASMAN/NZ
Spring grass growth should flush in NZ this week.

A trough and front crossing Tasmania today, 14 Sep, should cross South
Tasman Sea on Mon and Tue, proceeded by a NW flow that will be wet for
Southern Alps and dry and warm further east over the South Island. The
front should cross NZ on Wed followed by a SW flow on Thurs and Friday.
Avoid this front.

A HIGH moving east across Australia is expected to follow that front and
cross the Tasman Sea on Wed/Thu /Fri along 35S and the cross central NZ
on Sat Sun 20/21 Sep. This HIGH should be followed by another NW flow
then another front early next week - a typical spring pattern


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 2008

BOBGRAM7 issued 7 Sep 2008

WEATHERGRAM
YOTREPS
Issued 7 Sep 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

TROPICS AND SUBTROPICS
South Pacific Convergence Zone SPCZ is steady in strength and patchy in
coverage... It is strongest about Papua New Guinea and Solomons...
Another burst of activity at times between Tokelau and Samoa, and
occasionally over north Tonga, then it sort of stretches from about
Suvarov to midway between Southern Cooks and French Polynesia. There
has been a squash zone between the SPCZ and a Big fat high recently-this
squash zone still affects Southern Cooks to Niue with strong trade winds
and rough seas.
Highlight of the coming week to look for is for a build up in activity
near Suvarov on wed 10 Sep UTC moving South onto Southern Cooks by sat
13 UTC, There will enhance that squash zone even further, with tropical
squalls on its north side and steep big swells on its south side, so I'd
say it IS NOT the week to sail from French Polynesia to Tonga, unless
you like riding a bucking bull.

When this system moves off to the south early next week, it may pave the
way for a Low to possibly form about or south of Niue then SW towards
Niue early next week. After that we may have a good weather for sailing
westward ho!

Rest of the South Pacific between Tonga and Australia is looking OK this
week-a gentle subtropical ridge along 30S and average trade winds mainly
along 20S. Computers are picking some kind a drawn out surface trough to
form south of New Caledonia and extend towards Kermadecs by Friday---
probably caused by an upper Jet Stream and - this trough is forecast to
cross Fiji and Tonga on 14 and 15 Sep utc, but not much in it until it
possibly forms that Low south of Niue early next week.


NZ/TASMAN AREA
In a reversal of pattern back to winter NZ had a ridge over the weekend
(frosty in places) and is following up with a LOW from the Tasman Sea
this week. The frontal zone is likely to cross the North Island on
Monday and may linger across the south end until Thursday and the Low
itself slowly works its way in pieces across central NZ. On the north
side of this LOW, over the North Island, will likely be squally
westerlies from Tuesday til Thursday. A Southwest flow should clear the
weather over NZ on Friday and then the outlook is for another ridge of
light winds for next weekend.

Conditions should be OK for sailing from NZ to Fiji/Tonga after the
Monday front, but wait til Friday if sailing NZ/New Caledonia.
Best day this week to sail Tonga to NZ would be, depending on your
cruising speed, around Mon/tue utc -so that you encounter that trough at
around 30S on Fri 12th, and time you arrival in NZ with a SE flow
maintained by that weekend ridge.

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

31 August 2008

BOBGRAM7 issued 31 Aug 2008

WEATHERGRAM
YOTREPS
Issued 31 August 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

TROPICS
South Pacific Convergence Zone SPCZ is building in strength over Papua
New Guinea and Solomons. Further east there are two branches-one from
Tokelau to Northern Cooks along around 10S, and t'other sort of in the
Tonga/Kermadecs region, stretching east along 20/25S to a peak south of
French Polynesia.

SUBTROPICS
The pattern is dominated by the Big Fat High BFH east of NZ this
weekend. It is rare to find a 1040+hpa anticyclone in our part of the
world - I can't seem to find a tele-connection between it and GUSTAV in
Gulf of Mexico, suffice it to say that planet Earth is going through
some extreme weather at present. We in MetService have a saying, when
High above 1030, weather will get dirty... so when High above 1040,
weather will get naughty. The squash zone between this High and the low
that will form on its NW shoulder (as they do) will be particularly
intense over the Kermadecs area on Monday and Tuesday. Fiji Met has
already issued a gale warning on this.

The Low that forms south of Fiji/west of Kermadecs on Monday is forecast
to wander south/southeast to east of Chathams by Sat 6 Sep as the High
wanders east. There's another squash zone on the north side of this
High, and it'll reach its peak over Southern Cooks on the 6/7 Sep
weekend UTC w and strong easterly winds from Tuamotu to Southern Cooks
and with 4m+ swells around Southern Cooks . AVOID.

NZ AREA
Next trough rolling in from Tasman Sea is a trough between two Highs, so
this is a new pattern for us - a change from those lows that have been
forming in Tasman Sea and dumping rain on us. The trough should bring
rain to western South Island and gusty NW to eastern NZ from Mon to Thu
---stalling a while as a secondary low forms near Brisbane--and finally
secondary low and trough should cross the North Island on Thu and Fri
and maybe Sat and Sun. Avoid departing/arriving Northland Thu-Sun.

Sailing NZ/Fiji, Tonga? Wait until the Low has gone, after 4 Sep.
Sailing NZ/Noumea, looks OK.
Sailing Eastern Aussie? Not good this week, wait for that Low off
Brisbane has gone.

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

29 August 2008

BOBGRAM7 issued 24 Aug 2008

WEATHERGRAM
YOTREPS
Issued 24 August 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

TROPICS
South Pacific Convergence Zone SPCZ had another quiet week and is most
active along 10South - Papua New Guinea to northern Vanuatu and southern
Tuvalu to Tokelau to Northern cooks to northern Tuamotu. This still
means that those hopping west from French Polynesia should go via
Aitutaki or Niue rather than the Suvarov way.
The subtropical ridge, to east of 180, is strongest along 30S, so the
trade winds are enhanced about half-way in-between, along 20S.

Some of the SPCZ occasionally connects with a mobile east-ward
travelling mid-latitude trough. One of these connection-troughs is
crossing New Caledonia today, 24 Aug, and should visit Tonga on
Tuesday/Wednesday, Niue on Thursday and Southern cooks on Friday UTC
this week. These passing troughs are preceded by a period of light
variable mainly NE winds, accompanied by a few tropical squalls, and
followed by a re strengthening of the SE trade winds. There has been a
near weekly rhythm to them recently.

SUBTROPICS
It is time for another HIGH to makes its way eastwards across the Tasman
Sea - That one over eastern Australian coast today (sun 24 Aug) is
expected to weaken away as it moves NE across the Tasman Sea towards
Norfolk Island on Monday to Wednesday - Just not enough oomph. A weak
front is forecast to move east across Tasmania on Tuesday UTC followed
by a HIGH with oomph, that should cross the south Tasman Sea at 45S on
Friday and the South Island on Sat and be east of North Island by Mon 1
Sep.
Early next week there are signs that a low /trough may form in the Fiji
area and wander southwest towards eastern New Caledonia.. Not sure about
this yet, but if it does happen then there will be a squash zone of
enhanced easterlies between this trough and that HIGH , mainly around
30S between Kermadecs and Norfolk Island. Maybe worth avoiding.

NZ/TONGA AREA
It is still winter here in NZ, but the deepest depth of cold was , it
seems, 9-10 August, just after the start of the Olympics if you can
remember back that far. The LOW crossing North Island Monday/Tuesday is
followed by a southerly affecting southern North Island mainly in
Tuesday/Wednesday. The remainder of the week is dominated by the
incoming HIGH.

Nothing much to watch out for, in sailing to/from Northland this week.
Just remember about the possible Kermadecs to Norfolk squash zone that
MIGHT form early Sept.

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

16 August 2008

BOBGRAM7 ISSUED 17 August 2008

WEATHERGRAM
YOTREPS
Issued 17 August 2008
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

TROPICS
South Pacific Convergence Zone SPCZ is going through a quiet time at
present and has broken into a few disconnected branches. One stretches
from Papua New Guinea to Vanuatu and occasional feeds showers over
northern parts of Fiji. Another stretches from between Samoa and
Tokelau to the Northern Cooks and occasionally breeds showers between
Tuvalu and Wallis/Futuna in the west or over Tuamotu group in the east.
This means that those hopping west from French Polynesia should go via
Aitutaki or Niue rather than the Suvarov way.

Easterly winds dominating the whole South West Pacific, both north and
south of the SPCZ. There is likely to be a squash zone of enhanced
trade winds over western half of Coral Sea (and the Great Barrier Reef)
especially on Wednesday and Thursday in response to a HIGH then crossing
the Tasman Sea. Not comfortable.

Some of the SPCZ occasionally connects with the mobile east-ward
travelling mid-latitude troughs. One of these connection-troughs is
likely to visit New Caledonia on Friday and Saturday 22-23 August, and
may affect parts of Fiji/Tonga on Sunday 24 August. These troughs
bright light variable winds and a few tropical squalls. Today's
computer output is picking intense squalls around the NW of New
Caledonia on Friday 22 August but this may change by then.

SUBTROPICS
It is time for another HIGH to makes its way eastwards across the Tasman
Sea - and the next one is forecast to form in the Tasman near 30S on
Tuesday. This HIGH should cross Norfolk Island on WEDNESDAY and
Kermadecs on Friday and be south of French Polynesia on Sunday 14 August
UTC-there will be enhanced trade winds at 20S to north of this High.

The High is expected to be followed by a trough that will cross reach
Sydney on Thursday then cross the Tasman and then NZ on Saturday/Sunday
(yep another wet Saturday). AT this stage the HIGH following this
trough (next week's HIGH) is expected to take the 35SOUTH latitude.

So, there are reasonable weather patterns for crossing the Tasman
either way : next week's HIGH may be a slightly better choice for
sailing westwards to Brisbane, and this week's trough does offer an
opportunity from sailing eastwards across the Tasman.

NZ/TONGA AREA
Heaviest snowfalls in the Arthur's pass and Ruapehu areas of NZ since
the early 90s (and the Pinatubo eruption) - caused by a deep LOW that
stalled over southern NZ taking southern ocean air and swinging it north
into the Tasman Sea then in a westerly flow onto NZ. We meteorologists
call it mmP or modified maritime Polar (kiwi will get the pun about mmp
in an election year). But nope, this winter, in spite of all the wind
rain and cold doesn't get to break any records or hop on any medal
podium - we've had wetter, colder and windier winters in NZ. It's just
the snow that stands out, and that's due to mmp.

A system forming over the North Island today (Sunday) will deepen into a
LOW below 990 east of the North Island on Monday and this system is
forecast to LOOP and deepen further on Tuesday, exposing eastern North
Islanders to a sting of enhanced wet cold southerly winds (avoid).
Thursday is the best day of the week in NZ for light winds and a
reasonable sunny day for golfers.
The next trough is likely to start off on Friday with heavy rain for the
Southern Lakes with its NW flow on Friday, followed by west to SW
showery weather on Saturday and Sunday. Avoid.
Best days to depart/sail from northern NZ for Tonga are Monday/Tuesday.
Best day to depart/sail from Tonga to NZ is Tuesday (for a vessel
capable of up to 6kt).

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

09 August 2008

BOBGRAM7 issued 10 August 2008

WEATHERGRAM
YOTREPS
Issued 10 August 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

TROPICS
South Pacific Convergence Zone SPCZ continues to linger at the northern
end of its range, along 10 South latitude from Solomons to Tuvalu, and
should spring to life from Tokelau to northern parts of French Polynesia
later this week.
This means it is lingering near Suvarov, so those hopping west from
French Polynesia should go via Aitutaki or Niue rather than the Suvarov
way.

Some of its moisture occasionally branches off to the south and mixes
with the mid-latitude troughs as they travel from west to east.
One of these mid-latitude troughs visited New Caledonia and Fiji last
week, and another is likely to reach New Caledonia on Monday 11 August
UTC and brush past Fiji on Wed 13 Aug UTC. These troughs are reasonably
mediocre, but they do bring periods of variable wind.

SUBTROPICS
Between these troughs we have subtropical ridges/Highs, these were weak
over past few weeks but are becoming more noticeable now. They are
migrating from west to east mainly along 30 s. One is over North
Island/ Kermadecs today/Monday 11 Aug UTC and should be south of French
Polynesia on Thu 14 Aug, and the next is likely to blossom sat 30S south
of Southern Cools around Sat 16 Aug UTC. North of these highs there is
a zone of enhanced trade winds in the tropics especially around 20S.

SO, trade winds in the tropics this week go up and down in speed as
ridge and troughs pass by in the subtropics Otherwise it is likely to be
a weak of trade winds in the SW Pacific.

TASMAN/NZ AREA
T'was good to see the sun over NZ today from that passing ridge - first
in many weeks. But it was a cold High and didn't last long. The LOWS
are still deepening in the Tasman Sea, but they are not blocked like
they were in late July.

Next Low is already deepening near Sydney today 10 Aug and its fronts
are expected to cross NZ late 11 and on 12 Aug UTC with the LOW crossing
the South Island. This should be followed by a disturbed westerly flow,
with another front on Thu 14 Aug UTC and a LOW affecting southern parts
of Tasman Sea/NZ on 16-17 Aug followed by cold southerlies. Avoid
these fronts and lows. The westerly to southerly winds in the Tasman Sea
again this week will make it hard for anyone wanting to sail to Sydney.

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

03 August 2008

BOBGRAM7 issued 3 Aug 2008

WEATHERGRAM
YOTREPS
Issued 3 August 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

TROPICS
South Pacific Convergence Zone SPCZ is well no from the northern part of
Solomons to Tuvalu/Tokelau to Northern Cooks. It'll probably start to
extend southwards this week and get to Samoa next weekend.

Some of its moisture is likely to branch off to the south across the
Coral Sea on Thu 7 Aug (all dates UTC) and join with a trough then
crossing the Tasman Sea so that a wet trough reaches New Caledonia on
Fri 8 Aug (in time for start of the Olympics) - accompanied by variable
winds and squally showers -- and this trough will then move southeast
across Kermadecs on Sat 9 Aug. Also on 8 Aug UTC another trough
(rather weak) is likely to move eastwards across French Polynesia
accompanied by some squally showers and variable winds.

Otherwise it is likely to be a weak of trade winds in the SW Pacific.

TASMAN/NZ AREA
The LOW that passed over NZ last week was a slow-mover. It was blocked
by a zone of higher pressures to south and east of it. Blocking is
something that adds grunt to NZ's winter storms, and it looks as though
it may hang around for the next few weeks. So a few more Lows from the
Tasman are on the menu - but this week there'll first be a break in the
pattern with a passing High.

This incoming HIGH will bring us a welcome break in the recent wet windy
weather. It's sitting over eastern parts of Australia today (3 Aug) and
expected to peel off into the Tasman on 4th then wander over NZ on
5-6-and much of 7th with dry weather and light winds. Good for fishing.

On Thu 7th the next trough will start deepening in the Tasman Sea,
preceded by northerly winds, accompanied by rain, and followed by
squally SW winds. This trough is likely to cross NZ on 8-9 Aug,
followed by a disturbed west/southwesterly flow on 10-11 Aug, turning
colder southerly on 12-13-14 Aug.

The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

26 July 2008

BOBGRAM7 issued 27 July 2008

WEATHERGRAM
YOTREPS
Issued 27 July 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

TROPICS
South Pacific Convergence Zone SPCZ is hugging the 10 South latitude from Solomons to Tuvalu/Tokelau, and was also reasonably active last week from Northern Cooks to French Polynesia FP - it should relax over FP this week.

I made a typo last week saying "There are Northeast to easterly winds on its northern side and southwest winds on its southern side."  That should have been SOUTHEAST winds on its southern side - the ordinary trade winds-but they are under strength at present, and the SUNTROPICAL RIDGE is well NORTH of its normal winter position (of 25South) with one centre at 20S over the southern Cooks and another forming near New Caledonia by Friday. The High over Southern Cooks is expected to migrate to 35S 140E by the end of this week. 

The reason for this deviation from norm is that COLD POOLS are forming aloft over the Tasman Sea --- These cold pools are diverting the subtropical ridge to the north.   This is knocking the main latitude belt of the 20 knot trade winds to between 10 and 20 South, and opening places such as New Caledonia to occasional frontal passages.

The clouds and trough for the next of these frontal passages are already gathering offshore of Brisbane.   The northern end of this frontal zone is expected to cross New Caledonia on Monday and Fiji/NZ on Tue/Wed.  Avoid.

TASMAN/NZ AREA
Last week's low from the Queensland area was "NO ORDINARY STORM" and deepened to 963 hPa as it crossed Northland yesterday, moving quickly east/southeast.

This week's low, forming near Lord Howe Island on Monday, is expected to deepen to 983 by the time it reaches New Plymouth area on Wednesday, and by then to be more wide-spread than last week's low... but it is likely to be blocked so that it takes its time crossing central and southern NZ on Wed Thu and Friday, followed by squally west or Southwesterlies over the weekend of 2/3 Aug.  Avoid.

This closes down any comfortable sailing around the Tasman Sea/NZ area for another week or more.

The terms used here are more fully explained in the METSERVICE Yacht Pack.   Feedback to bob.mcdavitt@metservice.com

19 July 2008

BOBGRAM7 issued 20 July 2007

WEATHERGRAM
YOTREPS
Issued 20 July 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

TROPICS
The South Pacific Convergence Zone is hugging 10 South latitude from
Solomons to southern Tuvalu/Wallis - Futuna to Samoa, and is indistinct
further east, in the region between Southern Cooks and French Polynesia.
There are Northeast to easterly winds on its northern side and southwest
winds on its southern side.
Not much variation in this theme this week, except for a development
between Queensland and New Caledonia-a LOW is expected to form offshore
of Queensland on Wednesday 23 July. EC model picks this low to go east
past New Caledonia on Fri 25 July then southeast past Raoul Island over
the weekend. GFS model picks that the low may deepen to 985 hPa near
Norfolk Island around 12ooUTC Friday 25 July and then skirt past NE
parts of NZ over the weekend. There will be a gale force squash zone of
easterly winds on the southern side of this low, so AVOID, please.


MID LAITUDES
The best day of the week for sailing around NZ will be Monday 21 July as
a weak ridge passes by.

A LOW deepening to below 970 hPa to east of Tasmania on 21/22 July has
its cold front crossing NZ on 22 July followed by the LOW and its
squalls on 22/23 July and then a strong cold southerly flow on 23/24/35
July in time for that LOW from near Queensland to do a fly-by over the
weekend. So it's too unsettled for any voyaging to or from NZ from Tues
22 until at least the end of the month.

A HIGH in the Aussie Bight on Monday is expected to move east across
Victoria on 22/23/24 July and into South Tasman Sea and south of NZ on
24/25 July. This HIGH feeds cold southerly winds onto NZ, and there will
be a squash zone of enhanced easterly winds on its northern side
interacting with that low from the Queensland coast.

NOTE: I am on leave until 28 July but will be checking my email this
weekend 26/27 July.

The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

13 July 2008

BOBGRAM 7issued 13 July 2008

 

WEATHERGRAM

YOTREPS

Issued 13 July 2008 NZST

Bob McDavitt's ideas for South Pacific sailing weather.

(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).

 

 

Just a quick weathergram this week—I have people staying here for teh weekend and limited time to look at the weather.

 

 

TROPICS

The South Pacific Convergence Zone is increasing in activity especially over eastern Solomons and extends from there to Wallis /Futuna and then southeast across the Niue/Southern Cooks area...the eastern section of the zone is likely to spread north onto Samoa this week.

 

 

MID LAITUDES

Not a good week for sailing across the Tasman Sea. We have disturbed weather in the Tasman - with a front reaching NZ on Tuesday and a Low and front on Friday and Saturday.

 

NOTE:  I am on leave from on 14 and 15 July and then again from 18 to 25 July so next weathergram may be delayed a while and I’ll be unable to do any voyage forecasts during that time.

 

The terms used here are more fully explained in the METSERVICE Yacht Pack.   Feedback to bob.mcdavitt@metservice.com

 

 

05 July 2008

BOBGRAM7 issued 6 July 2008

WEATHERGRAM
YOTREPS
Issued 6 July 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

Galapagos to Marquesas: For the late comers: Head direct for 4S 96E
then go straight. This will avoid the strong east-going current and use
the winds best: winds are SE over Galapagos and turn easterly to west of
110E. Be on watch for a few tropic squalls between 120W and Marquesas

TROPICS
The South Pacific Convergence Zone is going thru a quiet time now. It
starts the weak active along a zone from Papua New Guinea across
Solomons and northern Vanuatu to Fiji and Niue and to the southeast.
The section east of the dateline is expected to be active on Mon UTC and
then fade away from Tuesday UTC. There is another branch of the SPCZ
near10S from Tokelau to Marquesas. This is more properly known as a
shear line. It has lighter easterlies to its north and strong easterlies
to its south, anyway it is breeding thunderstorms so be wary there.

A mid latitude low is expected to deepen in the cold air that is being
shunted into the subtropics--- near 33S 155W on Thu or Fri UTC. This
will activate the SPCZ between Tahiti and Southern Cooks into a trough
with squally showers.

SUBTROPICAL RIDGE

HIGH above 1028 crossing the central Tasman Sea along 40S next few days
and NZ on Wed 9 July UTC will enhance the trade winds to north of it
into a squash zone. This Squash zone should cross New Caledonia on 7-8
July and over Fiji-Tonga-Niue from 9 to 13 July UTC. Take care.

MID LAITUDES
A cold pool moved onto the North Island this weekend in tandem with a
deepening surface low off the east coast- bringing the coldest day of
the winter so far on Saturday, with snow and ice closing many roads.
It'll be a hard winter storm to beat, perhaps this winter's nadir.

Weather window is ripe early this week for heading from NZ to Fiji/Tonga
and for coming the other way as well.

One last southerly wind change with showers rippling along NZ east coast
on Monday, then a few days with light winds- frosty morning and sunny
day- from a passing HIGH.

Next front /trough should form off the Australian Coast on Tue 8 July
UTC and reach the South Island on Friday 11 July UTC preceded by NW
winds - good rain for the hydro lakes- then the North Island on Sat 12
July UTC followed by a westerly flow.

The next front, due over the North Island on 14 July may have strong
wind and rain, and will be followed by SW winds. This one is worth
avoiding; one of the computer models is developing a LOW with it.

NOTE: I am on leave from 9 to 15 July, so next weathergram may be
delayed a while and I'll be unable to do any voyage forecasts during
that time.

The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

28 June 2008

BOBGRAM7 issued 29 June 2008

WEATHERGRAM
YOTREPS
Issued 29 June 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

Galapagos to Marquesas: just as last week, head direct for 4S 96E then
go straight. This will avoid the strong east-going current and use the
winds best: winds are SE over Galapagos and turn easterly to west of
110E.

TROPICS
The South Pacific Convergence Zone is going thru a quiet time now. It
is still active around northern Coral Sea and has a few flashes of
activity across northern Vanuatu and west of Fiji. There is a weak
branch from Samoa to French Polynesia. A brief burst of heavy rain is
likely Sunday/Monday about and southeast of Kermadecs from a passing
front.

SUBTROPICAL RIDGE
A large HIGH is being calved eastwards from Australia but is likely to
shrink as it crosses the Tasman Sea on Monday and Tuesday however it may
expand again east of the dateline on Thu and south of French Polynesia
on Friday Saturday. This High will enhance the trade winds north of it
as it migrates eastwards. Next HIGH is likely to leave Australia on
Sunday 6 July, and should take a path slightly further south.

Mid Latitudes
Last week brought one northerly front, one thundry then one windy
westerly front, and finally a southerly (with a low). That southerly
will peel off to the east on Monday, and that's when a brief ridge will
bring some frosty sunshine to the South Island. Tuesday's the North
Island's turn for a light-wind/sunny break.

The next broad trough is set to move across Tasman Sea/NZ on Wednesday
to Saturday, with its main front on Thursday, and cold southerlies over
South Island on Friday/North Island on Saturday. Avoid this front.

The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

21 June 2008

BOBGRAM7 issued 22 June 2008 NZST

WEATHERGRAM
YOTREPS
Issued 22 June 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

Galapagos to Marquesas: head direct for 4S 96W then go straight. This
will avoid the strong east-going current and use the winds best: winds
are SE over Galapagos and turn easterly to west of 110W.

TROPICS
The South Pacific Convergence Zone quietened down last week. There was
some increase in activity over Papua New Guinea but some fading in
activity to north of Fiji. This section is expected to drift south onto
Fiji this week, but should not be as strong as it was earlier this
month. A branch of the SPCZ was almost along the some latitude from
northern Tonga to French Polynesia, and this section is expected to
drift north.

There are strong southeast winds in the Coral Sea, and these are being
maintained by the anticyclone that is stalling over Australia. From New
Caledonia to French Polynesia the subtropical ridge is weak and has been
shoved north to 25S, so the trade winds are also weak in this part of
the tropics.


Mid Latitudes
A real wintry week for NZ.

The trough referred to in the last weathergram has arrived over the
North Island. As it moves off to east of the South Island on Monday,
its southerlies will be cold enough to bring some mountain snow.

A southerly jetstream is starting to show itself over Tasmania at
present and this is expected, late Tuesday, to bring unusually cold
southerly winds from to southern ocean onto NZ--- with squalls and
showery show, and with some dollops to sea level.

In the wake of this, on Wednesday to Friday, it looks like a disturbed
westerly flow with gales and heavy swell in the Tasman Sea. Avoid.

On Saturday a LOW is likely to deepen near Chatham Island, bringing
another southerly to NZ for the weekend. There may also be some
reasonable trips from Northland to Fiji/Tonga departing Wednesday -
these trips will experience some squally westerlies and heavy swell near
North Cape.

The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

14 June 2008

BOBGRAM7 issued 15 June 2008

WEATHERGRAM
YOTREPS
Issued 15 June 2008
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

I should have mentioned last week that weathergram.blogspot.com is an
ADDITIONAL way to get this weathergram. I'll keep emailing them as
well.

Galapagos to Marquesas: Back to other route this week-head direct for
4S 96E then go straight. This will avoid the strong east-going current
and use the winds best: winds are SE over Galapagos and turn easterly to
west of 110E.

TROPICS
The South Pacific Convergence Zone was active last week- and showing
signs of a pulse of extra convection. It mainly extends from Papua New
Guinea to Solomons to Fiji and then faded further to the southeast. A
trough moving along the SPCZ brought heavy rain to Fiji and this is
finally moving off tonight 15 June. This week the SPCZ is expected to
drift north and should affect Samoa to Southern Cooks/southern French
Polynesia.

Mid Latitudes
Hmm, the trough I was talking about last week to "fade away" on Friday
13th in the Tasman Sea, didn't do that-it stalled and, over the weekend,
has been deepening near Lord Howe Island to below 1000, making a heavy
southerly swell on its western side. Well it is now expected to move
east and fade to north of Northland on Thursday. Its fronts should
attack northern and eastern North Island on Monday and Tuesday. Avoid
these fronts and be mindful of this Low. There is a companion low to
southwest of Fiji tonight - and it should follow those fronts onto
northern Northland and fade away.

That new big-fat-High over Victoria today is expected to spread east and
cross the South Island on Tuesday-Wednesday and to expand as it moves
over Chathams and further east on Thursday-Friday-Saturday. This will
enhance the trade winds between Southern Cooks and Fiji for a few days.
Loos at this stage that a low might form on the northwest shoulder of
this BFH, as they do, and that will be to south of Southern cooks,
taking that squash zone south-wards.

After the BFH, there will be a large trough filling the entire Tasman
Sea next weekend in time for this year's winter solstice, and moving
onto NZ early next week. We will look at that in the next weathergram.

The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

07 June 2008

BOBGRAM7 issued 8 June 2008

WEATHERGRAM
YOTREPS
Issued 8 June 2008
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

NEWS: I'm now publishing the WEATHERGRAM at
http://weathergram.blogspot.com so if you want one by email send an
email to query@saildocs.com, no subject required, saying SEND
http://weathergram.blogspot.com

Galapagos to Marquesas: New suggested plan: because the winds are
mostly south-south-east around Galapagos to 105W use these to hop north
to the equator and sail westwards along the equator: Avoid the strong
east-going current between Equator and 3 degrees S. Near Equator 105 to
110W head SW - there is less current here - and from 5S 120W to
Marquesas to winds start to turn to be south-easterly.

TROPICS
The South Pacific Convergence Zone was rather quiet over the Coral Sea
recently, and is now slowly returning to that area. It has been more
active than normal over Fiji and in a broad band from there across Tonga
and Niue and parts of the Southern Cooks. This branch of the SPCZ is
forecast to wait for pressures to start falling between Vanuatu and
Fiji, as is likely to happen around Thu 12/Fri 13 June UTC. This
pressure fall is then likely to trigger a rapidly deepening LOW that
will move off to the SE - across the Kermadecs on Sat/Sun 14-15 June
UTC. There will be a squash zone between this low and the High to the
south--- strong enough to generate gale East /NE winds and heavy swells
for a time. Avoid this LOW and its squash zone.

The tropical extension of the trough associated with this low is likely
to reach Tonga on 15 June UTC / Niue on 16 June UTC / and fade over
Southern Cooks on 17-18-19 June UTC , preceded by a weak NE winds,
accompanied by tropical squall and followed by a return to trade winds.

Anyone sailing from French Polynesia westwards will need to sail through
that SPCZ.

Mid Latitudes
The Big Fat High BFH in the Tasman Sea is expected to cross the North
Island on Wednesday - with a squash zone of enhanced trade winds on its
northern side between 170 W and 170E mainly along 20S. When this BFH
moves off to the East on Thursday and Friday it is expected to induce a
fall of pressure on its northwest shoulder-that will be between Vanuatu
and Fiji, triggering the low mentioned above. Avoid this low.

So this BFH turns out to be NOT the best scenario for sailing from NZ to
Fiji or Tonga... but OK for sailing from NZ to New Caledonia or eastern
Australia. The trough following the BFH in the Tasman Sea on 11-12 June
is expected to fade away on 13 June. Not like that trough which brought
heavy rain to Queensland last week.


The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

31 May 2008

BOBGRAM7 issued 1 June 2008

WEATHERGRAM
YOTREPS
Issued 1 June 2008
Bob McDavitt's ideas for South Pacific sailing weather.
(Standard 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).

TROPICS
The South Pacific Convergence Zone is sitting in a zone from Solomons to
Rotuma to Samoa to midway between Suwarrov and Rarotonga, with Northeast
winds on its northern and eastern side and tropical squalls along its
length. On Tues 3 June UTC the northern end of the trough leaving NZ
will brush past Tonga, drawing the SPCZ south onto Fiji. And on
Wednesday this front will brush past Niue, so that from Thursday the
eastern flank of the SPCZ is expected to between Niue and Rarotonga
offering a challenge to anyone sailing through that area.

South and east of the SPCZ the trade winds are being well maintained.
The subtropical ridge is strongly represented along 30S, sometimes
enhancing the trade winds, especially along 20S.

Galapagos to Marquesas: Satellites are reading a strong east-going
current between equator and 3 degrees S, so get south of that ASAP.
Winds are mostly southerly around Galapagos, so set off to the
Southwest. West of 110 W the winds gradually turn easterly, so head off
for something like 4S 100W then go straight.
It is showery between 110 and 120 W.

MID LATITUDES.
The front moving northeast across the eastern coast of NZ is likely to
slow and develop a small low to east of Wairarapa on Queen's Birthday
Monday, making some intense showers over the North Island. This is
expected to be followed by a disturbed southerly flow all week, with
another front moving NE along eastern coasts on Friday 6 June. Avoid
these fronts.

The HIGH in the central Tasman Sea today, Sun 1 June, is a slow- mover
and must wait its turn - will likely to cross NZ on 9-10 June. It is
blocking that low that did form off the Brisbane coast, as picked in
last week's weathergram. This low, or trough, is expected to hang
around for a few more days and deepen to around 1012 near Lord Howe
Island on Friday 6 June and then fade away. Be aware of it if you are
crossing the North Tasman Sea, but it's not expected to produce much-
maybe some squally gales.

The terms used here are more fully explained in the METSERVICE Yacht
Pack.
Feedback to bob.mcdavitt@metservice.com

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