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

05 March 2011

BOBGRAM7 issued 6 March 2011

WEATHERGRAM
YOTREPS
Issued 6 March 2011
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.

People in Christchurch have moved from rescue to recovery mode, remember
them at christchurchearthquakeappeal.govt.nz

TROPICS
La NINA is still strong, and steady. Its 30day running mean moved from
2.14 on 26th Feb to 2.19 on 5 March .

There are falling pressures and persistent convective rain over much of
northern Australia, consistent with a new MJO pulse that is expected to
move into the Coral Sea from late this week. Standby for another period
of active weather in SW Pacific next week and until after the Equinox.

South Pacific Convergence Zone SPCZ as returned to its normal position
and is basically sitting over the Coral sea and Northern Vanuatu, coming
and going over Fiji and Tonga and more consistent over Niue and to south
of Southern cooks.
Some BUT NOT ALL models are picking that a series of tropical
depressions may form on SPCZ especially around Vanuatu, Coral Sea and
Gulf of Carpentaria this week. Keep an eye out but do not get diverted
by model extrapolation just yet.
If you have internet keep an eye on http://bit.ly/ecoz for comparative
purposes.


SUBTROPICAL RIDGE:
We seem to be moving into the magical equinoctials already. With the
sun now close to being directly over the equator, the subtropical ridge
is doing a good job in the South Pacific of mixing cool air northwards
and warm air southwards-what we call more 'meridonal' rather than
'Zonal' patterns. Energy is starting to move from the planetary waves
(1 and 2) into the long waves, especially Wave 4. This does mean more
weather in terms of wind and rain between some of the individual high
cells of the STR.

This week in our area HIGH1 is tonight in the South Tasman Sea east of
Tasmanian. There is a squash zone of enhanced trade winds on the north
side of HIGH1 and south side of SPCZ--and Fiji Met have a gale warning
out on this zone for tonight/Monday. HIGH1 should wander east along
around 42 south and fade east of the south Island by Thu 10 March, and a
sub-cell is likely to cross the North Island on Fri 11 March and then
fade away.

HIGH2 is expected to cross Tasmania around Thu 10 March and then rotate
around south end of South Island by Sat 12 March and then get east of NZ
early next week - the Northerly flow on its "backside" is likely to open
a pathway to NZ for whatever may then be forming in the Coral Sea then.
More on this in the next weathergram.


NZ Area
We have had a trough cross NZ over the past few days-it has been
meridonal enough to bring 'southerly rain' to eastern North Island, the
first in about a month to do this, pleasing pastoral farmers and
displeasing apple-pickers.

A small low centre is expected to form within that trough tonight,
making for a day or so of southerly gale on the Hawke's Bay/Gisborne
Coast-good that the restart from Napier for last leg of Round North
Island Race will take off on Monday after this gale.

For remainder of this week there may be a southeast then easterly flow
over northern NZ (this may strengthen over the 12/13 March weekend) and
a disturbed westerly flow over southern NZ. Inbetween places may have
morning mist areas. A weak trough between HIGH1 and HIGH2 is expected
to fade over the South Island Friday.

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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