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

19 June 2011

BOBGRAM7 issued 19 June 2011

WEATHERGRAM
YOTREPS
Issued 19 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.


TROPICS
SOI is in neutral territory, in past few weeks its 30day running mean has risen from 0.18 on 5 June to 0.73 on 12 June then fallen back to 0.26 on 19 June.

Monsoon is making reasonably average progress over India. There may be a tropical cyclone forming east of Philippines and this feature is expected to go NW and make landfall on China but, at this stage, it isn't expected to become intense.

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. There are some tropical showers north of Marquesas from 135 to 145W mainly along 3S, but these will probably not affect the voyage. But if you are attempting the Panama to Galapagos leg, be aware that ITCZ is strong to south of Panama along around 5N.
South Pacific Convergence Zone SPCZ is having a quite time — some disorganised slumps east of the dateline, and a more organised line stretching from south of Solomons across Vanuatu then SE to south of Fiji where it merges with a mid-latitude trough/front which is travelling eastwards. This trough may trigger the development of a low to south of French Polynesia around 30S 125W towards the end of the week, bit otherwise it looks like a week of trade winds in the Southwest Pacific, good for sailing west.


SUBTROPICAL RIDGE STR
There is still a leftover high in high latitudes, south of the low now crossing NZ — this high should travel northeast to 40S 140W by next weekend.

The STR generally seems to have finally shifted to its normal winter position of between 30 and 40S (it is about time, Tuesday is solstice). There are big gaps between its highs, one high is south of French Polynesia FP today and moving off to the east, enhancing easterly winds over FP. The next is making its way across central Australia and should shoot off a bud along 25S on Tuesday/Wednesday then move into central Tasman Sea along 40S next weekend, causing strong trade winds in the Coral Sea.

TASMAN SEA/NZ AREA
Last lot of cold air in the weekend trough is expected to wander east across North Island on Monday.
Then a weak ridge is expected to cross NZ on Tuesday/Wednesday.
Next 'Roaring 40s trough' should move across Tasman Sea on Tuesday and arrive over NZ from Wednesday night- waves of squally showers until a drying but cold southerly arrives next weekend (as high moves into Tasman Sea). This is likely to bring some useful snow at last to NZ ski fields.

SAILING TO/FROM NORTHERN NZ.
Best day to depart this week is Tuesday. And best day to arrive is Wednesday.

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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