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

19 November 2011

BOBGRAM issued 20 Nov 2011

WEATHERGRAM
YOTREPS
Issued 20 November 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.

La Nina continues in a weak to moderate fashion. From the atmosphere, the Southern Oscillation Index SOI is positive and hovering near 1: On 11 Nov it was 1.02, AND ON 18TH, 0.90 Computer modelling suggests it will continue into the southern hemisphere cyclone season, but as a minor player, making a quieter than normal cyclone season.

The first tropical depression of the new cyclone season made its appearance during the past week, bringing several days of heavy rain to northern Fiji and moving across central Tonga. It has moved off to the southeast and faded away now.

The South Pacific Convergence Zone SPCZ has two branches: one from Solomons to north of Vanuatu to north of Fiji, and the other from Tuvalu to Samoa to Southern Cooks. The SPCZ that is now north of Fiji is likely to move onto Fiji and Tonga this weekend 26/27 Nov.

SUBTROPICAL RIDGE STR
The High that has been lingering in north Tasman Sea for past two weeks is finally on its way east, but slowly and will still be able to form a squash zone between it and the front over the South island on Monday—making gusty conditions for central NZ and wet conditions wit that front. Avoid.

This high then mainly lingers at 30S 180, waiting for a Low to go east of NZ, and finally the High is expected to move off to east itself on Wed/Thu 24/25 Nov.

New High is expected to move across Tasmania on Thu 24 Nov and weaken as it extends across northern NZ on Fri/Sat 25/26 Nov

TASMAN SEA/NZ AREA
On Monday there is an enhanced front + squash zone, a classic spring front, to avoid. A low is expected to form between Christchurch and Chathams on Monday and deepen as it goes east. Another front is expected to cross NZ on Wed 23 Nov, followed by strong SW flow on Thu 24/ Fri 25 Nov (with large ocean swells) and then winds should ease for the election weekend.

SAILING TO/FROM NORTHERN NZ.
If you have Internet access you may be able to check the weather patterns at bit.ly/7daywx or bit.ly/ecoz

For Northland there is, at this stage, expected to be a northerly flow for much of next week, so plan to come south as that high waddles off to the east on Thu 25 Nov and plan to get to Opua before the next SW change (somewhere around 3 Dec).

I plan to be in Nelson for Coastguard conference next weekend… this may delay my next weathergram, depends on how well I travel.

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

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