Translator

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

29 May 2010

BOBGRAM7 issued 30 July 2010

WEATHERGRAM
YOTREPS
Issued 30 May 2010
Bob McDavitt's ideas for sailing around the South Pacific.

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

NORTH PACIFIC
TC AGATHA starts off the new North American Cyclone season, rolling into
Guatemala from the Pacific Ocean and its rain is turning ash from a
recent volcanic eruption to some sort of ready mix concrete.
GALAPAGOS TO MARQUESAS
Not much change from last week... Take off to just north of the equator
at first, and go to around 125W, and enjoy a following current and a
moderate wind from south or southeast. Then head direct for your
destination and winds should oblige at southeast 15 knots.
TROPICS
South Pacific Convergence zone SPCZ, after having most of its energy
taken off into the mid-latitudes last week, is slowly reforming now
along 10S, from Papua New Guinea to east of Solomons to Tuvalu/Tokelau
and extending to Samoa at times.
A combination of clouds from the tropics + jetstream intensification + a
large upper low feeding mid-latitude fronts resulted in a lot of
thunderstorms between Fiji and New Zealand last week, no doubt harassing
the Auckland to Fiji race fleet.
This week a trough is likely to form over Vanuatu on Thu/Fri 3/4 June
and deepen into a low to east of New Caledonia on Sun 6 June. The Low
should then get caught in a jetstream and shoot southeast and deepen
rapidly as it crosses the Kermadecs on Mon 7 June - avoid it then.
SUBTROPICAL RIDGE: STR
The High currently crossing southern NZ should wander along 40/45S
eastwards and get south of French Polynesia mid next week around 10
June. There is a rather mediocre zone of enhanced trade winds on its
northern side.
Next high to wander along the STR should also take the 40S latitude but
is likely to extend eastwards as a tongue rather than as a closed
centre... reaching Bass Strait from Tue 1 June to Thu 3 June and Central
NZ from Friday 4 to Saturday 5 June, just in time for start of NZ
Queen's Birthday holiday weekend.

TASMAN/NZ
Between the Highs mentioned above come the lows. Last week's lows took
their time to cross NZ, so that we had an opening gambit of strong NE
winds and rain last Monday, then a middle game as the rain band
spiralling into the centre stalled over South Island, and finally a
squash zone/eggbeater moulded by the low and the incoming High.

The next low has deepened off Sydney on schedule as picked in last
week's weathergram, but isn't as well positioned as last week's low to
develop much further. It will however take its time as it crosses NZ
and split into a multi-centred system on Tues 1 June.

For those waiting in Northland to sail off north, the useful SW winds
should arrive there on Thu 3 June. There may be another front crossing
Northland on Fri 4-Sat 5 June with a change to southerly/southeast
winds. Sun 6 June could be light winds at Northland, and then there
may be Ok winds for sailing north again on Mon/Tue 7/8 June. Enjoy.

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 May 2010

BOBGRAM issued 23 May 2010

WEATHERGRAM
YOTREPS
Issued 23 May 2010
Bob McDavitt's ideas for sailing around the South Pacific.

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

GALAPAGOS TO MARQUESAS
Take off to just north of the equator at first, and go to around 125W,
and enjoy a following current and a moderate wind from south or
southeast. Then head direct for your destination and winds should
oblige and be southeast 15 knots. may be some tropical shower activity
around Marquesas this week.

TROPICS
South Pacific Convergence zone SPCZ was very active across Vanuatu/New
Caledonia to South of Fiji/Tonga last few days. A burst of convection
has been captured by northwest winds aloft and is wandering across
Vanuatu today (Sunday) and should then wander to the southeast, getting
to 998 very close to the Kermadecs on Tuesday morning and then fading
and heading south. This is the low that we were picking for the
Auckland to Fiji Yacht race would be at 981 near North Cape on Monday
night and would bring 8 metre + swells to near 30S on Tuesday - under
this new path the swells in that region then will be more like 4 metres.


There is another branch of the SPCZ stretching from Wallis/Futuna to
Tuvalu to Tokelau. This branch is expected to wander southwards across
Fiji on Monday and then across Tonga on Tuesday and Wednesday. Later in
the week a new SPCZ should reform over Papua New Guinea and Solomons.

SUBTROPICAL RIDGE: STR
High 1 has its cell east of New Zealand (we enjoyed it here on
Saturday), and is on its way to the east and should reach French
Polynesia longitudes on Thu/Fri 27/28 UTC with a squash zone of enhanced
trade winds on its northern side.

The STR is weak after that high, as the Tasman Sea turns into a low
breeding ground. High2, a cell east of Tasmania is all that is left in
our part of the STR and it will be forced to wait, and finally squeeze
across to south of NZ on Thu 27 May. For those waiting for the STR to
reassert itself across the Tasman Sea so that they can have a
comfortable voyage from Auckland to the tropics--- indications are, at
this stage, that you may need to wait til early June. I think the STR
tends to fade like this whenever there is a kerfuffle in the Sea Surface
Temperatures around Galapagos.
.

TASMAN/NZ
When the STR is weak the Tasman Sea becomes a low breeding ground. Last
Thursday night's low got to 999 near North Cape.

Low 1 for this week is 1005 in mid Tasman today and should drop to 985
as it crosses Cook Strait on Tuesday/Wed 25/26 May. At its peak on
Wednesday when centred east of Marlborough, there will be squally
westerlies and heavy swell over western NI, but of more importance will
be the squash zone between Low 1 and High 2 (referred to above). This
flow will drive SE winds directly onto the eastern SI, mixing cold and
moisture in a chamber of lowering pressure: a formula good for mountain
snow on the eastern slopes of our Alps.

Low 2 for this week should roll across New South Wales on Tue, be around
1005 near Lord Howe on Wed 26 May, 1001 near Norfolk on Thu 27 May and
1005 near North Cape on Friday 28 May. The squash zone between Low 2
and High2 should bring a large zone of easterly gales onto the eastern
NI during the 29/30 May weekend. This combination will make for a
larger impact that last Thursday's 999 low near North Cape. Avoid.

Low 3 should deepen offshore Sydney on Sat 29 May, making for a real
southerly buster: avoid.

I made a late night typo last week, so here's a correction: Those of
you who have email at sea can download the latest NZ high seas forecast
by sending an email to query@saildocs.com, no subject needed, with
message SEND http://bit.ly/subtropic, as well as listening to it on
ZLM.

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 May 2010

BOBGRAM7 issued 16 May 2010

WEATHERGRAM
YOTREPS
Issued 16 May 2010
Bob McDavitt's ideas for sailing around the South Pacific.

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

GALAPAGOS TO MARQUESAS
Take off to just north of the equator at first, and go to around 124W,
and enjoy a following current and a light southerly wind. Then head
direct for your destination and winds should obliging increase to 15
knots from the southeast or east. Weather mostly settled; some showers
around 92W and 100W. Also very showery along the Intertropical
convergence zone between 5 and 9N so don't stray that far away.

TROPICS
South Pacific Convergence zone SPCZ has been knocked around lately and
that zone of cloud and squalls stretching from off Queensland to south
of Fiji and then out to the southeast is a reflection of the subtropical
jet rather than the SPCZ.

The SPCZ is slowly reactivating around the Solomons to Tuvalu and around
Northern Cooks to French Polynesia. There is a burst of active
convection over Indonesia at present but that will take weeks to get
into the Pacific and is more likely to affect Micronesia rather than
South Pacific.

However, we should remember that squalls in that trough line south of
Fiji can still be a problem. I had an email today recording a good 35
knots of winds around 160 miles south of Suva. So keep in mind that
the GRIB files and isobars don't work 100% near troughs.

SUBTROPICAL RIDGE: STR
HIGH1 from last week continues to dominate proceedings and is 1038 at
40S 150W... should continue to wander east reaching 090W next weekend
with a touch to north to 33S where it will become the Andes High for a
while. As mentioned last week, there is a strong squash zone of the
northern side of High1--- many yachts were sheltering from it in Minerva
all last week. This squash zone is exacerbated between High 1 and a low
that has formed to southeast of French Polynesia - Fiji Met have just
issued a gale warning on this zone. The Low is blocked and is likely to
move south then southwest and fade into the next incoming trough of Tue
18 May.

Next High along the STR is barely showing itself as it crosses New
Caledonia tonight 16 May, and south of Fiji and Tonga on Tue/Wed 18 /
19 May and then should be more noticeable south of Southern cooks at
30S by 20 to 21 May.

Following High in the STR will be more to the South, rolling along 45S
to south of Tasmania on 20 May, heralded by a southerly outbreak that
may toss cold southerlies with rain then snow onto southern New Zealand
from Fri 20 to Sun 22 May.

TASMAN/NZ
Large Catherine-wheel low in the Tasman Sea is rotating clockwise
underneath its cut-off upper low and should finally cross NZ on Tue 18
May and its associated trough should reach Northland on Wed 19 May
followed by only brief SW winds.

Next trough rolls in from the southern ocean onto South Island from Fri
20 to sun 22 May, pushed in by that high in the STR, as mentioned above.


The Jet stream over Queensland looks primed to produce another Tasman
Low. Latest GFS model has this crossing the Tasman and reaching NZ
around 26 -27 May, but the latest EC model http://biy.ly/ecoz has its
warm fronts reaching NZ around 23 to 24 May, and that seems closer to
the observed recent rhythm in the STR. Those preparing for the Auckland
to Fiji race taking off on Sat 22 May will be keeping a close eye on
these models, and the http://bit.ly/7daywx model all during the coming
week.

Those of you who have email at sea can download the latest NZ high seas
forecast by sending an email to query@saildocs.com, no subject needed,
with message SEND http://bit.ly/suntropic, as well as listening to it
on ZLM.

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

09 May 2010

BOBGRAM7 issued 9 May 2010

WEATHERGRAM
YOTREPS
Issued 9 May 2010
Bob McDavitt's ideas for sailing around the South Pacific.

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

GALAPAGOS TO MARQUESAS
Take off to just north of the equator at first, and go to around 110W,
and enjoy a following current and a light southerly wind. 110W marks
an area of squally showers this week. After 110W head direct for
Marquesas (Nuku Hiva or Hiva Oa) and winds should obliging increase to
15 to 20 knots from the southeast, with settled weather.

TROPICS
South Pacific Convergence zone SPCZ is starting to reactivate this week
after a quiet time. It stretches across Papua New Guinea and Solomons to
northern Vanuatu, and this branch is expected to stretch to be across
Fiji and Tonga on Tue/Wed 11/12 May There is another branch from east
of Samoa to Southern Cooks, and this is likely to take a rare wandering
onto French Polynesia on Thu/Fri 13/14 May.

SUBTROPICAL RIDGE: STR
HIGH1 that moved east of New South Wales over the weekend is being
shunted over central New Zealand on Mon 9 May and should wander steadily
eastwards along 40S to east of NZ for the remainder of the week, with a
squash zone of enhanced trade winds on its northern side that should
affect southern Cooks from Wed 12 to Sun 16 may.

Then the STR goes through a weak period. The next High is expected to
wander across the eastern Australian Coast line on Sat/Sun 15/16 May,
just in time to kill the wind for Ella's Pink Lady as she arrives in
Sydney.

A small wedge of this ridge may get east along 22-23S to New Caledonia
and south of Fiji on 15/16 May and that will be preceded over New
Caledonia and Fiji by a period of light southerlies and clearing weather
on 12-14 May

TASMAN/NZ
Weather window for comfortable sailing out from Northland is closed this
week.

Low1 to northwest of Northland has to wait for High1 referred to above
to get east. So it's doing a loop tonight/ Monday and should then
travel south along 170E on Tue/Wed 11/12 May, fading as it crosses
Southland.

Around this time a large trough is expected to cross Tasmania, followed
by a very cold southerly that will be originating from the Antarctic ice
shelf- a polar outbreak. This trough should form a new low in mid
Tasman Sea on Thurs 13 May, and this low should cross central NZ on 14
to 16 May, with that polar outbreak fading as it arrives over the
southern South Island on Fri 14 May.

When a Low deepens like this in the Tasman Sea as it approaches central
New Zealand, it is able to draw in moist warm air and cool it with fresh
cold air: this is a well-known scenario for rain in NZ, so take time
out to clear those gutters of autumn leaves in readiness.


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 May 2010

BOBGRAM7 issued 3 May 2010

WEATHERGRAM
YOTREPS
Issued 3 May 2010
Bob McDavitt's ideas for sailing around the South Pacific.

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

GALAPAGOS TO MARQUESAS
There is a build up of cloud around Galapagos at present, so maybe wait
a few days before departing if you like. Take off to just north of the
equator at first, and go to around 110W, and enjoy a following current
and light southerly winds. Do not go any further north than around 30
minutes north... After 110W head direct for Nuku Hiva, the entry port
for Marquesas, and winds should obliging increase to 15 to 20 knots from
the southeast, with settled weather.

TROPICS
South Pacific Convergence zone SPCZ is having a quiet time at present,
so enjoy this while it lasts... It is slowly reorganising across the
north end of the coral sea and then in a zone from Tuvalu to Southern
Cooks, but at present reasonably clear over Samoa. Should continue to
build and hold position this week, and may spread south towards Fiji
some stage next week 10-14 May.

A LOW is expected to form at the mid-latitude end of the SPCZ to south
of Southern cooks around 6-9 May and peel off to the southeast.


SUBTROPICAL RIDGE: STR
HIGH in Tasman Sea is expected to fade near western North Island and
then be reinforced by another HIGH on Monday 3 May. New combo High
should cross the central NZ area 4-5 May and then wander off to east of
North Island on 6-7 May . There will be a squash zone of enhance trade
winds on the north side of this High mainly along about 23 South from
around Niue to New Caledonia.

Following this High there should be a trough T1 that will cross NZ on
Fri/Sat 7-8 May. Then, from 8-12 May a HIGH is expected to migrate from
central Australia along 30S across northern Tasman sea. This will build
the STR and allow for some strong westerlies south of it over NZ next
week - a step towards winter in the south.

TASMAN/NZ
Not bad for heading off over next few days, but window closes by Thu 6
May.

Mediocre cold front on Monday 3 May, High on 4-5 May, then comes that
trough T1 referred to above.
Preceded by strong northerlies on Thu 6 May and followed by disturbed
westerlies from Sat 8 May.

Some models make more of this tough than others , occasionally hinting
at chance of a low between New Caledonia and Northland early next week.
This is an unsure scenario at present, and if it impacts on your
venture then do the double-check.


TASMANIA / NEW SOUTH WALES COAST
ELLA'S PINK LADY is now on last leg of a circumnavigation, with a
solo-sailor (still under 17). For her there's one more challenge, as
that trough T1 referred to above (due to cross NZ 6-8May) crosses
Tasmania and New South Wales on Tue-Wed 4-5 may. When the trough
interacts with the east Australian current this may generate some lows,
and these will peel off to South-southeast into the southern Ocean, but
one of them may deepen rapidly east of Tasmania on Wed 5 and generate a
large zone of gales, typical of any classic Sydney-Hobart. Then that
HIGH mentioned above should kill all the wind near Sydney on the 8-9
Weekend.

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

Blog Archive