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

30 January 2010

BOBGRAM7 issued 31 Jan 2010

WEATHERGRAM
YOTREPS
Issued 31 Jan 2010
Bob McDavitt's ideas for sailing around the South Pacific.

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

The South Pacific Convergence Zone SPCZ means business again this week.

The remains of OLGA are still stewing away in the heart of Australia and
turning tropical air into rain, good for a change in that part of the
world but maybe too much of a good thing in some places because it is so
slow moving. The Coriolis force should help it go south by next
weekend.

NISHA came and went, sort of a one to two -day wonder. However, the
pulse of extra energy which helped NISHA to form is probably good for
other one or maybe two tropical lows. One is over Tokelau area at
present--- dominating the SPCZ and might deepen further as it tracks
southeast towards the French Polynesian area by around 3 or 4 Feb.
After that moves off, another Low may form in the Wallis/Futuna area
during the 6-7 Feb weekend.

There is a zone of westerly winds along 5 to 10S across the South
Pacific. The trade wind easterlies have shifted southwards to between
20 and 40 South. This makes the zone between 10 and 25S somewhat
lacking in wind - with the SPCZ near 10S and a counterbalancing zone of
sinking dry air along 20S - right over Fiji Tongs. This dry zone of
light winds does wander about and let the wet clouds of the SPCZ pass
through it at times, especially over Niue and Southern Cooks.


SUBTROPICS/NEW ZEALAND
The South Pacific subtropical ridge SPSR has taken an excursion
southwards to around 40 to 50S near the dateline and become
slow-moving-held in place by the orientation of the upper flow. The
squash zone on its northern side is along 30S, between New Caledonia and
NZ, and by the end of the week the strong winds in this zone should have
built a big sea from Raoul Island to Norfolk and Lord Howe Islands.
Avoid.

Some fronts will attempt to punch this High away over Southern NZ on Tue
2 Feb and Sat 6 Feb but seem set to fail. The easterly winds over
northern NZ may get strong at times, including during the Auckland
anniversary day Regatta on Mon 1 Feb. A twisty trough over past day and
tonight has provided/ is providing some rain to Northern North Island,
but is likely to dry out during 1 and 2 Feb.

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

23 January 2010

BOBGRAM7 issued 24 Jan 2010

WEATHERGRAM
YOTREPS
Issued 24 Jan 2010
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.

It looks to me that we are about to enter the business part of the
cyclone season.

TC OLGA came from an extra burst of convection that started over Solomon
Islands and followed the path as described in last week's weathergram,
and seems to have temporarily cleared the Coral Sea of its clouds... It
may go thru a reintensification in the Gulf of Carpentaria on Monday 25
Jan and bother people south of Darwin on Thursday 28 Jan.

The South Pacific Convergence zone SPCZ has reformed in its normal El
Nino position from around Tuvalu to Tokelau, between Northern and
Southern Cooks and across southern French Polynesia. Something
different about it this week is the likely appearance of a zone of NW
winds on its northern side especially in the zone between Samoa and the
Cooks. This is likely to make the area between Samoa and Niue a
breeding ground of tropical lows in the next week or so. Computer
models are struggling to resolve exactly where these tropical lows may
form, and it could be around the Rotuma/Futuna area. Any low that forms
is most likely to track southeast-wards towards Niue. Avoid and keep
updated.

SUBTROPICS
A new cell in the South Pacific Subtropical Ridge SPSR is moving across
South Island on Mon 25 Jan --- then moving further east along 40S past
Chathams on 26-27 Jan - It will continue eastwards along 40/45S, so that
early next week there will be around 50 hPa of isobars between its
centre and the centre of the Low coming south form the Niue area, making
for a large and intense squash zone between 30 and 40S well to east of
NZ. This squash zone should generate large swells which will be
arriving along North island east coast.

Surfs up for Auckland's anniversary weekend right thru to Waitangi Day.

NEW ZEALAND AREA:
The arrival of that cell in the SPSR marks an end to the recent
unsettled weather and the beginning of a week or more of summer-like
conditions just as we approach the period of the year that normally has
the warmest days.

For South island it looks to be a week of warm maybe muggy northerly
winds, mostly dry so prepare for an increasing fire risk.

For North Island's north half, the humid easterly turning northeast flow
should bring some welcome showers, especially during their
anniversary-holiday weekend 30 Jan to 1 Feb when a trough may add a
clockwise twist to the wind flow.

South end of the North Island has a dying southerly for its anniversary
holiday on Mon 25 Jan and then a humid northerly for the rest of the
week, varying between sunny and cloudy, and adding several degrees to
the overnight low. Summertime, at last.


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 January 2010

BOBGRAM7 issued 17 Jan 2010

WEATHERGRAM
YOTREPS
Issued 17 Jan 2010
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.

A weakening MJO or Madden Julian Oscillation of extra convection is
making its way eastwards into the Papua New Guinea region this week.
This may well help feed the LOWS that are forming in the Coral Sea. One
of these LOWS may move southwest wards across Solomons on Fri 22, deepen
in the Coral Sea on Sat 23 and possibly make landfall onto northern
Queensland on Sun 24 Jan. Avoid.

The South Pacific Convergence zone SPCZ in the past week has been active
as a zone from around Tokelau to Northern cooks and French Polynesia,
and another zone the Coral ea to New Caledonia. There was a low that
took rain to south of Southern Cooks, but also a large very dry area
over Fiji and Tonga, stretching to Vanuatu and Samoa. Activity is very
intense between Solomons and the Equator-connecting to the ITCZ
International Tropical Convergence zone--- this is where a zone of
equatorial westerly winds is busy brewing boisterous bubbly clouds.

SUBTROPICS
There is a subtropical high near 40S 150W are to south of French
Polynesia with a weak subtropical ridge towards the Kermadecs at the
start of the week but that is fading.
Tasman Sea area is predisposed to low pressure this week, blocking the
start of a new subtropical ridge, but one should form across northern
Tasman Sea and last from 21 to 24 Jan

NEW ZEALAND AREA:
Continuing unsettled: Those damp cold southerlies we mentioned in the
last weathergram brought some minor wind damage to parts of Wellington
yesterday.
Next LOW is expected to deepen a lot in mid/south Tasman Sea Mon to wed
18 to 20 Jan and then weaken as it crosses central NZ from Thursday to
Saturday. Most of its wind and rain is wrapped up with its fronts,
crossing North island on Wednesday/Thursday, but the LOW is also likely
to be followed by a strong and showery southwest flow on Friday and
Saturday 22-23 Jan. Plan around it.

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 January 2010

BOBGRAM7 issued 10 Jan 2010

WEATHERGRAM
YOTREPS
Issued 11 Jan 2010
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.

A new Madden Julian Oscillation of extra convection is making its way
eastwards across Northern Australia, It almost triggered a tropical
low last Mon 4 Jan, but that bunch of cloud went for a visit into the
Aussie interior instead bringing them some welcome rain, but helping to
displace some desert air towards the south Coast (Melbourne and Geelong
hit the low 40s over weekend).

Some souped-up activity is expected to move into the Coral Sea this
week. There is already a branch of the South Pacific Convergence zone
in the Coral Sea and I think this will start breeding low pressure areas
by the 16-17 Jan weekend. Watch this space.

The South Pacific Convergence zone SPCZ started last week in a zone from
Samoa to the French Polynesia FP area. Mid=last-week a low formed over
Southern Cooks, as mentioned in last week's Weathergram, and moved off
the southeast. The cooler drier southerly flow and rising pressures on
its western side has dried out the SPCZ between FP and Fiji for a few
days, but a new zone is now slowly forming along 10S.

SUBTROPICS
After a week or more of strong subtropical ridges, we may now be due for
a week or so of weaker ridging in the Tasman Sea area.

The High well east of NZ at 170W today should remain strong centred
south of 45S and drift to around 150W by the 16-17 Jan weekend, with
enhanced trade winds returning to the Southern Cooks to Tonga area as a
consequence.

The next-high-to-the-west: over Tasmania today, is expected to just move
north and fade over the Lord Howe area on Thursday 14 Jan. A new high
should then bud across Tasmania and bring another dry weekend as it
crosses northern NZ on 16-17 Jan. As this high moves off next week: IF
the resulting falling pressure coincides with one of those lows or
troughs that may form in the Coral Sea, then there is a likelihood of
some rain from the subtropics reaching Northland where it is needed, but
too far away to be sure yet.. more in next weathergram.

NEW ZEALAND AREA:
Unsettled: A LOW has formed east of Otago on today's front: it should
bring cold (and maybe damp) southerlies to eastern areas until
Wednesday. Then the next front should move onto the South Island on
Thursday, and develop a low east of Canterbury on Thursday night (local)
with damp cold southerlies for eastern areas until Saturday.

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

03 January 2010

BOBGRAM7 issued 4 Jan 2010

WEATHERGRAM
YOTREPS
Issued 4 Jan 2010
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.

This edition is later than normal as I've be travelling around during
past week. I'm back to normal now.

There is some sign of extra energy way out west over next week--- a Low
moving onto Australia from the Timor Sea and what may well be a Tropical
Cyclone forming in Indian Ocean near 85E around Wednesday 6 Jan.

It looks to me as if we will have another reasonably quiet week in the
South Pacific. South Pacific Convergence zone extends from Solomons to
Samoa to Southern Cooks/French Polynesia. A tropical Low may form over
Southern Cooks area around Thursday 7 Jan and move slowly southeast and
fade by Tuesday 13 Jan--- may be gale winds between this Low and the
subtropical ridge on its south side, but the systems will likely "steal
" the wind around Niue and Cooks and may produce a squally northerly
wind over French Polynesia.

Trade winds over remainder of South Pacific should be average, but from
around 9 Jan , winds should become variable around the Coral Sea and
there may be a westerly flow over Papua New Guinea and Solomons, the
start of another build-up of tropical energy.

SUBTROPICS
HIGH in Tasman Sea should squeeze across northern NZ on Tuesday 5 Jan
and then move southeast to 40S / 160 to 140W on 7 - 8 Jan and then go
northeast. This high is tracking along the subtropical ridge which
extends from this High along 35/ 40S all the way to high that is at 30S
west of South America.

Next High rolling in from the Australian Bight is expected to cross
Tasmania on wed/Thu 6-7 Jan, and then cross central NZ on weekend of
9-10 Jan. People in Central NZ should plan to enjoy the outdoors this
weekend (last one was too windy with passing fronts).

NEW ZEALAND AREA:
A front is expected to cross NZ on wed/Thu 6-7 Jan, preceded by strong
NW flow and followed by SW winds. Next front is likely around southern
South Island on Sun 10 Jan. Avoid these winds if you can.

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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