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

26 July 2008

BOBGRAM7 issued 27 July 2008

WEATHERGRAM
YOTREPS
Issued 27 July 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

TROPICS
South Pacific Convergence Zone SPCZ is hugging the 10 South latitude from Solomons to Tuvalu/Tokelau, and was also reasonably active last week from Northern Cooks to French Polynesia FP - it should relax over FP this week.

I made a typo last week saying "There are Northeast to easterly winds on its northern side and southwest winds on its southern side."  That should have been SOUTHEAST winds on its southern side - the ordinary trade winds-but they are under strength at present, and the SUNTROPICAL RIDGE is well NORTH of its normal winter position (of 25South) with one centre at 20S over the southern Cooks and another forming near New Caledonia by Friday. The High over Southern Cooks is expected to migrate to 35S 140E by the end of this week. 

The reason for this deviation from norm is that COLD POOLS are forming aloft over the Tasman Sea --- These cold pools are diverting the subtropical ridge to the north.   This is knocking the main latitude belt of the 20 knot trade winds to between 10 and 20 South, and opening places such as New Caledonia to occasional frontal passages.

The clouds and trough for the next of these frontal passages are already gathering offshore of Brisbane.   The northern end of this frontal zone is expected to cross New Caledonia on Monday and Fiji/NZ on Tue/Wed.  Avoid.

TASMAN/NZ AREA
Last week's low from the Queensland area was "NO ORDINARY STORM" and deepened to 963 hPa as it crossed Northland yesterday, moving quickly east/southeast.

This week's low, forming near Lord Howe Island on Monday, is expected to deepen to 983 by the time it reaches New Plymouth area on Wednesday, and by then to be more wide-spread than last week's low... but it is likely to be blocked so that it takes its time crossing central and southern NZ on Wed Thu and Friday, followed by squally west or Southwesterlies over the weekend of 2/3 Aug.  Avoid.

This closes down any comfortable sailing around the Tasman Sea/NZ area for another week or more.

The terms used here are more fully explained in the METSERVICE Yacht Pack.   Feedback to bob.mcdavitt@metservice.com

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