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

11 July 2010

BOBGRAM7 issued 11 July 2010

WEATHERGRAM
YOTREPS
Issued 11 July 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.

TROPICS
South Pacific Convergence zone SPCZ is still quiet but slowly activating
along 10S from Coral Sea, in clumps, all the way to Northern Cooks and
Marquesas. It has been hugging to 10S latitude, but occasionally links
south with mid-latitude fronts, making wet troughs --- one affected the
Cooks on 7 and 8 July and another affected Fiji on 9 and 10 July. This
latter trough is expected to continue eastwards and finally fade out
between Cooks and Marquesas on 15 and 16 July Thu/Fri. Anyone heading
west from Marquesas to the Cooks, or south from Tonga or Fiji to NZ will
need to factor this trough into their plans.

There is a low; lets call it L1, which has formed with the trough that
was over Fiji last night. This Low is near 30S 180 and should move
steadily south along the 180.

Total Eclipse: Clouds seem to be keeping away from the area that will
become a total eclipse at 111830UTC near Maria Island in the Tuamotus
(and Mangia Island in the Southern Cooks). Easter Island is currently
partly cloudy and clearing, but there is a cloak of cloud heading that
way, so fingers crossed there.

SUBTROPICAL RIDGE: STR
High over 1030 crossing NZ this weekend is likely to wander off to the
east between 40 and 45S getting as far east as 140W by the end of this
week. This is so far south that it isn't likely to enhance the trade
winds on its northern side-but there will be a squash zone between it
and L1 that is worth avoiding.

Next high upstream will be slow to appear, and is likely to bulge east
off southern Queensland around Fri/sat 16/17 July, stretching east along
25/30S to get to 180 by Tue 20 July. This northern latitude STR will
help enhance a westerly flow over NZ.

TASMAN/NZ
Yes, we got polar air over NZ this weekend, as mentioned in the previous
weathergram; it was mainly dry but did manage to bring us the lowest
temperatures we have seen this winter.

As L1 comes south over next few days, the eastern North Island are
likely to get a dose of cold southerly rain, especially on Wednesday
/Thursday 14/15 July.. But the low should be further away than last
week's, and hopefully will have less impact.

There are some nice tail winds around L1 for anyone wishing to sail
northwards from Northland. These winds will fade away by Wednesday and
then turn northwest and then strong westerly for the remainder of the
week.

A winter /Southern Ocean Low is expected to deepen off Tasmania on Wed
14 July and then head northeast out of the south Tasman and onto the
South island / central NZ on Sat 17 July, followed by a disturbed
southerly and then a Southwest flow.

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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