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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

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