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

02 May 2011

BOBGRAM7 issued 2 May 2011

WEATHERGRAM
YOTREPS
Issued 2 May 2011
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas 6are from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Apologies for a delayed edition this week, was too busy travelling on
Sunday.

TROPICS
La NINA is still active in the atmosphere. The Southern Oscillation
Index 30day running mean weakened last week from 2.55 on 23 April to
1.94 on 2 May

South Pacific Convergence Zone SPCZ spent last week in active mode near
20S across the Coral Sea and New Caledonia and to south of Fiji. A low
L1 developed on this zone last Friday, but too far south to be able to
feed off much warm sea... however it has deepened to around 994hPa over
past few days as it moved into central Tasman Sea - and should now
weaken to 1000 hPa as it crosses the South Island on Wed 4 May.

The band that has been appearing along 5S between 100 and 160W started
to break up in the past week. This suggests that reasonable voyages from
Galapagos to Marquesas may start appearing in the next few weeks.

SUBTROPICAL RIDGE:
AN intense 1032+ HIGH H1 was located at 45S 170W today (2 May) and its
squash zone (helped by a few 1005 hPa lows to the north) crossed North
Island mid-last week bringing enhanced rain to Hawke's Bay Coast and
enhanced foehn winds to western NZ between Hamilton and Westport. 'Twas
damaging stuff.

There has been a squash zone between H1 and L1. Not as bad as last
week's but very gusty easterlies on Sunday over northern NZ, leading in
L1's warm front.

The next High, H2, is stuck in the Australian bight for a while ----

NZ/TASMAN SEA AREA

--- and this is likely to allow the cooling southerly winds that it
shovels northwards into the Tasman Sea on Thu 5 May to trigger the
formation of a new Low L2. The models are inconsistent at this stage
with the path for L2 - most likely it will cross central NZ during
Mother's Day weekend, followed by a change to cooler and somewhat
squally W or SW winds, and making this a week of two lows for NZ.

WHEN TO DEPART NZ FOR FIJI/TONGA?
Around the middle of the week there is a gap of lighter winds between
the two lows-maybe OK for motoring north but not for sailing. From Thu
to Sat, the showery NW flow ahead of L2's trough will probably put off
most cruising sailors. There is likely to be some assistance with a SW
to SE wind change after that trough on late Sunday, but this may be
interrupted by a period of light winds in a weak ridge. SO there
appears to be NO great sailing voyages appearing at this stage.

Heading east from NZ is OK in that NW flow, but may be affected by the
NE wind and swell being generated and left behind by H1.

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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