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

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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