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

25 April 2010

BOBGRAM7 issued 25 April 2010

WEATHERGRAM
YOTREPS
Issued 24 April 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 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
Tropical Cyclone SEAN formed over the seas northwest of Australia in the
past few days, and I'm thinking it is likely to be the last of the
season, so sailors can now start to heed those tropical sirens.

South Pacific Convergence zone SPCZ has been active from Coral Sea
eastwards across New Caledonia / southern Vanuatu to Fiji to Tonga to
Southern Cooks. There has been some surface flooding around Fiji and
Tonga, and there is a burst of convection over Fiji tonight as a Low
forms in the SPCZ trough. - This LOW is expected to move southeast over
the Lau group on Monday 26 April then slowly east along the SPCZ between
20 and 23S and be south of the Southern Cooks next weekend 1-2 May.

SUBTROPICAL RIDGE: STR
HIGH cell east of New Zealand is stalled until Tuesday and will then be
reinforced and move east along 35 to 40 South to be well south of French
Polynesia for the 1-2 May weekend. There is a squash zone of enhanced
trade winds on the north side of this system around about 25S, just
south of the SPCZ. Avoid.

Next HIGH in the STR is expected to cross inland Australia rather than
the Aussie Bight. The longer nights are helping make colder denser air
over inland Australia and this high is likely to move from South
Australia on Tuesday 27 April to New South Wales on the 1-2 May weekend
to northern North Island on 4-5 May. This High will push trade winds
into the Coral Sea knocking the SPCZ to Solomon Islands / Tuvalu.

TASMAN/NZ
Low in Tasman Sea should intensify as it wanders off to the south on Mon
26 April. Associated front should reach the North Island by Tuesday and
stall between Northland and East Coast from then til Thursday bringing
some welcome rain.

Usually around this time of year there is a cold SW change that whooshes
across NZ and makes cruising sailors shiver, up-anchor and head for
warmer climes. This is similar to a front that swoops across California
in October, called the Californian flush. Well, it isn't expect to be
very dramatic, but a deep Southern Ocean Low is expected to pass
eastwards to south of Tasmania on 27-28 April and south of NZ on 29-30
April and its associated front should bring a chilly SW/S change to the
South Island on Friday 30 April and North Island on Sat 1 May. So it
should be OK to depart NZ on 2 May.

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 April 2010

BOBGRAM7 issued 18 April 2010

WEATHERGRAM
YOTREPS
Issued 18 April 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
Best latitude with west-going current is just north of the equator from
Galapagos to 120W and then head direct for Fatu Hiva - winds are mostly
from SE around 10 to 15 knots. Reasonably clear of showers this week.

TROPICS
South Pacific Convergence Zone SPCZ is having a slight boost from a
passing Madden Julian Oscillation MJO. There was a burst of convection
over Vanuatu and New Caledonia last Friday 16 April, it is over Fiji
tonight 18 April and is forecast to go southeast, caught in an upper NW
flow. This burst should develop a small low south of Niue and northeast
of Kermadecs on Mon 19 April and that should wander off to the southeast
and deepen for the remainder of the week.

It is getting late in the cyclone season now and the chance of a cyclone
forming in the SW Pacific is starting to decrease, but raises up a touch
as this MJO has influence. Current indications are that there may be a
build up of convection in the Coral Sea during the coming week. This
cloud build-up may sweep onto Queensland and get captured by a trough
crossing New South Wales around Fri 23 April and then wash across
southern NZ as a warm/cold front combo on the 25 April. Or it may
follow last week's pattern and form a low over New Caledonia by 25 April
- maybe a bit of both. If a low does form and move onto New Caledonia,
then that raises the eyebrows to the possibility of a last gasp of a
seasonal cyclone.

SUBTROPICAL RIDGE: STR
HIGH cell in Tasman Sea has a squash zone of enhanced trade winds on its
northern side between New Caledonia and Queensland coast. It also
maintains a waxing-waning-southwester over New Zealand until Thu 22
April, which is when it should nose across the North Island. It then is
expected to wander off to east of NZ mainly along 40S from 23 to 30
April. That should be helpful to the sailing waka that have departed
Auckland heading for Tahiti.
The STR is expected to weaken after this high passes by, allowing a
pattern change in the Tasman Sea/NZ area to troughs, fronts and southern
ocean lows from 23 April to end of the month. People in the dry lands
around NZ have their tongues hanging out of this pattern change. And it
looks as though it'll arrive for some in time for ANZAC day.

Next HIGH in the STR is expected to cross inland Australia rather than
the Aussie Bight. The longer nights are helping for colder denser air
over inland Australia. This high is thus likely to get knocked inland by
the lows of the Southern ocean and so cross Australia from 28 April to 1
May.

TASMAN/NZ
Repeating the details above: a waxing-waning-souwester until Thursday,
then a warm/cold front combo over the South Island on Fri 23 April,
followed by a larger, more widespread, warm/cold front combo on Sun
25/Mon 26 April and a third on 28/29 April, possibly drawing in some
cloud from north Tasman Sea onto North Island around 30 April.
Unsettled enough to delay departures.

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

11 April 2010

BOBGRAM7 issued 11 April 2010

WEATHERGRAM
YOTREPS
Issued 11 April 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
Best latitude with west-going current is around 1 deg NORTH of the
equator... but it generally has light winds. There is occasionally a
zone of tropical showers near the equator from between 100W and 130W, so
take a latitude slightly further south for a useful sailing breeze that
generally has settled weather.
Intertropical convergence zone ITCZ is very active between 2 and 5N
from

TROPICS
South pacific convergence Zone SPCZ was last week indistinct and mainly
along 20S between southern Fiji and southern French Polynesia. There is
also a portion of SPCZ from North Queensland and across Papua New
Guinea/Solomons/and stretching to Kiribati/Tuvalu slowly building.

A low, left over from last week, Low 1, is located near 40S well to
south of Southern Cooks and is expected to travel east--- the tropical
section of the trough associated with this low - a zone of slack winds
and random squalls - is likely to cross Southern Cooks on Monday 12
April and stall over FP from 13 to 16 April.

A new low or trough, low 2,has developed on SPCZ to southeast of New
Caledonia and this system is expected to get captured by the trough
moving onto NZ, so that it should travel across eastern North Island on
Tuesday/Wednesday 13/14 April.

SUBTROPICAL RIDGE:
HIGH cell over Chathams has held some clean clear air over the North
Island over the weekend for a few days thanks to support from the upper
air. All this is changing now, and this High is expected to migrate
east along 40S this week and the get squeezed southeastwards around the
remains of Low 1.

Next High is over Aussie Bight and is a slow-moving system--- should
cross Bass Strait around Thu 15 April and then move northeast across the
Tasman and get squeezed so that it noses across northland around Sun
18-Mon 19 April

TASMAN/NZ
If you are about to head off north or east WAIT until the incoming
trough/front has gone - it is over Fiordland on Mon 12, very wet and
preceded by strong NW winds, then crossing rest of NZ 13-14 April. Also
WAIT for the cooler showery southwest flow that follows this front to
turn southerly over Northland and settle down - that makes Friday 16
April as best departure date this week.

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 April 2010

BOBGRAM7 issued 4 April 2010

WEATHERGRAM
YOTREPS
Issued 4 April 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
Best latitude with west-going current is around 1 deg NORTH of the
equator... but it generally has light winds. There is occasionally a
zone of tropical showers along 2 deg S between 100W and 130W, so take a
latitude slightly further south for a useful sailing breeze that
generally has settled weather.

TROPICS
South Pacific convergence Zone SPCZ has recently been indistinct and
mainly along 20S between southern Fiji and French Polynesia. A low
developed south of Fiji, throwing a squally westerly flow across Fiji.
This Low is now taking its tropical air southwards and is dancing along
the 180 deg dateline.

Last week's Tropical Cyclone TWENTY-TWO earned the name PAUL before it
went inland at SW end of Gulf of Carpentaria. PAUL had the wind knocked
out of its lower layers, but its upper low is still in place, and its
clouds brought more rain into the north and northeast corner of
Australia.

This activity over northern Australia is likely linked to a new Madden
Julian Oscillation or pulse of tropical convection. If so then we can
expect a build up of a new SPCZ during the next week or two over
Solomons and towards Vanuatu and between Tuvalu and Tokelau.
Another low is being picked to form near 20S late this week around Fri
9 April just south of Tonga and this system should wander off to the
southeast over the weekend. Otherwise, the coming week is looking OK
for sailing, with lots of average trade winds in the tropics.

SUBTROPICAL RIDGE:
HIGH cell that reached 1040 over Chathams last Monday is today south of
Southern Cooks and travelling steadily east along 38S and should reach
100W by Sat 9 April. It is taking with it a squash zone of enhanced
trade winds along 20-30S

Next HIGH is delayed by a weakness in the subtropical ridge over NZ.
This High is expected to arrive SOUTH of Tasmania on Mon 5 April and to
cross the South Island on 7 and 8 April, leaving behind a small cell in
the North Tasman Sea that is likely to cross the North Island from 9 to
11 April.

TASMAN/NZ
So, there is a weakness in the subtropical ridge around NZ this week,
and this allows lows to reach the region for the first time in weeks.
The Low moving southwards along 180 is expected to peel off to the
southeast from Mon 5 April, taking most of its rain clouds with it, but
helping showers to form over the dry lands north of Taupo.

Another LOW west of the North Island is expected to move northeast and
cross Northland on Tuesday 6 April, followed by a feisty southeast flow
that will likely bring a touch of snow to the mountain tops on 7 and 8
April. 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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