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

12 June 2011

BOBGRAM7 issued 12 June 2011

WEATHERGRAM
YOTREPS
Issued 12 June 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.

NOTICE: Those of you who are on my weathergram list will notice a
change: as from next week I will be sending these from
bobmcd@xtra.co.nz, and so some of you (depending on your settings) may
find these weathergrams in your JUNK folder. If so, simple tell your
email program not to junk bobmcd@xtra.co.nz

Also please note that I helping manage MetService display at Fieldays
and will be unavailable to respond to email 14-18 June.

TROPICS
SOI is in neutral territory, in past week its 30day running mean rose a
little from 0.18 on 5 June to 0.73 on 12 June.

Monsoon has arrived in Mumbai; arrival time is a few days later than
normal this year and so far accumulated monsoon rain is 17% above the
Long Period Average. It has developed a double-barreled low, one to
west of India in Arabian Sea is now Cyclone ADRIAN and t'other, to east
of India, sort of fills the entire Bay of Bengal.

Galapagos to Marquesas: More of the same. Avoid the Equatorial current.
Dive south to around 5S 100W and then head almost due west to 7S 133W
and then head for landfall. No organised tropical showers around. But
if you are attempting the Panama to Galapagos leg, be aware that ITCZ is
strong to south of Panama.

South Pacific Convergence Zone was mainly located from Tokelau to
Australs along with an active clump about and east of Tonga/Niue.
It also has a squash zone on its southeastern side at present (Fiji Met
Service gale warning). It is now mainly around the Northern and
Southern Cooks, and may get to French Polynesia FP and may get to Samoa.


The convergence over PNG links across the Coral Sea with a mid-latitude
trough that is quasi-stationary in Northern Tasman Sea and trails
southeastwards well to east of NZ. A weak 'secondary' low is expected
to wander from west to east along this front/trough line mainly along
30S to 35S from Monday to Wednesday. Not enough to stop sailing between
NZ and Fiji/Tonga but needs to be taken into account.

SUBTROPICAL RIDGE
High in Australasian Bight is about to break free from its block and
should get onto Tasmania on Mon 13 June and cross Tasman Sea to reach NZ
on Thu/early Fri 16/17 June, and then expand along 40S to east of NZ,
enhancing the trade winds from FP to Tonga early next week.
Next high from Australia is likely to wander east across New South
Wales, indicating a possible end to the "low index" weather regime we
have been having for a while. Colder SW winds should then be able to
spread further north across NZ.

TASMAN SEA/NZ AREA
Some cold air is sideswiping Southland and Otago tonight and should
reach Chatham Islands on Wednesday and Thursday.

Another Low is likely to form off Queensland coast by Wed 15 June, and
this one should deepen a lot in mid Tasman Sea on Thursday and then move
SSE across Southland on Sat/Sun 18/19 June. Associated front should
cross NZ area on late Friday/early Sat, preceded by a northerly flow,
accompanied by rain and followed by a showery NW flow.

For Fieldays this year, prospects are for a dying SW on Wed/Thu, a foggy
ridge for Friday morning, then a band of rain starting Friday night,
easing Saturday afternoon, then showers.

For those returning to NZ after the NZ-Fiji yacht race, you can use the
N to NW winds of the Friday/Saturday front to some advantage, and, at
this stage, it looks a though Northern NZ should then have light winds
Sun 19 to Wed 22 June so that should ensure a good enough return voyage.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

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