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

22 April 2012

BOBGRAM issued 22 April 2012

WEATHERGRAM
YOTREPS
Issued 22 Apr 2012
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.

The Southern Oscillation Index or SOI is now hovering in negative territory. On 8 April its 30 day running mean was -0.6 on 15 April it was -0.8, and on 22 April it was -0.6 again.

South Pacific Convergence Zone SPCZ has been moulded around a BIG FAT HIGH BFH that stayed near New Zealand last week. So there has been extreme convection along and just off Australia's East Coast. This convergence was also intense over New Caledonia and Fiji and then average convection over Tonga and from there to the southeast. Another convergence zone lingered along 10S between Tokelau and Northern Cooks, and another was active at times between 5S and the equator from 130 to 150W.

A small tropical low may form on the SPCZ on wed 25 April around 30S 175W … this system is likely to get pushed to the southeast by an upper Jetstream and should steal the winds off Tonga on Thursday.

Galapagos to Marquesas: There are squally patches between 110 and 115W otherwise OK. Depart quickly SSW from Galapagos until 3S then WSW to 6S then west to 125W then direct.

SUBTROPICAL RIDGE STR
The BIG FAT HIGH BFH that lingered over NZ for much of the past week is now slowly going east along 37/40S. Its western lobe should weaken over North Island on ANZAC Day Wed 25 April, allowing the remains of the now-intense trough that is currently in the west Tasman Sea to cross the NZ on Fri 27/Sat 28 April preceded by some NW winds and followed by W/SW winds. A passing Low in the southern ocean should bring a cold southerly outbreak to southern NZ on Sun 29 Apr.

Next HIGH is expected over Aussie Bight on Sat 28 April/New South Wales on Sun 29 Apr, and NZ on Tue 1 May.

NZ to Tropics: It looks to me that the cyclone season is over and this week is OK for sailing north. We may as well wait for that trough to cross North Island late on Friday and depart on Sat 28 to take advantage of the post frontal tail winds.

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

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