BOBGRAM issued 20 May 2012

WEATHERGRAM
YOTREPS
Issued 20 May 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 has bounced back into positive territory over the past few weeks. Its 30 day running mean started May at -1.1 but was plus 0.5 on 13 May and plus 0.2 on 20 May. It is erratic.

Indian Monsoon is one week ahead of its normal position. The Everest–climbing window seems to be around May 25th and could last shorter than normal this year. See http://explorersweb.com/everest_k2/news.php?id=20845

In the South Pacific, the Convergence Zone SPCZ has slowly activated its intensity across the Coral Sea and northern Vanuatu then splitting into two zones – one over northern Fiji and central Tonga, and another to south of Fiji and over Minerva. This southern zone is now easing and the northern zone is expected to move northwards to Samoa this week.

Next weekend around 26/27 May a low could form on the SPCZ over Southern Cooks and then move off to the south. This is something to go clockwise around for vessels on the NZ to French Polynesian route.

Galapagos to Marquesas: A continuation of last week, all clear of squally showers now. Depart quickly SSW from Galapagos until 3S then WSW to 5S then west to 125W then direct.

SUBTROPICAL RIDGE STR
The STR is weak, and has allowed a large Southern ocean Low to extend as far north as 30S to east of NZ during the past week. The cold air arriving over NZ has brought about the Kiwi version of the 'Californian flush' – a name given to the arrival of winter in California which triggers yachties to head for the tropics. The weather pattern still looks good for those who left late in the week for their trip to the north.

Next subtropical high is over New South Wales tonight and should slowly go east across Northern NZ on Tues to Fri 22/25 this week with disturbed westerly flow over the South Island.

NZ /Tasman Sea troughs
A LOW should deepen rapidly off Sydney on Fri/Sat 25/26 May and cross the Tasman Sea and then central NZ mid-next-week. Avoid.

Departing from NZ for the tropics:
On Monday a small trough, left over from last week's cold air, is expected over Northland with showers.
Then Tue/Wed 22/23 May are likely to have light winds in a passing ridge. Then Thu/Fri/Sat 24/25/26 May should see one of those fronts crossing the South Island get north to Northland. Then early next week will be upset by northerly wind and the fronts associated with the approaching low.

So there are no good departure days from Northland to the tropics this week.

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