BOBGRAM issued 31 July 2011

WEATHERGRAM
YOTREPS
Issued 31 July 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
Southern Oscillation Index SOI continues to slowly rise; its 30day running mean was 0.5 on 16 July and 0.6 on 22 July and 0.76 on 29th July.

Galapagos to Marquesas: If you are still looking at this voyage, it seems that there is a slight advantage with the wind to first head off to 3dge 30min S 100W and then to 6S 133W and then to Marquesas. Some showery activity is occurring on-and-off around Marquesas.

South Pacific Convergence Zone SPCZ is slowly returning after a weak period. The main band is affecting Solomons Vanuatu and Fiji. There are weak convergence zones along 3 to 5S, and near 15S between Samoa and French Polynesia.

Not much change with the SPCZ during the coming week, except for a low budding off to south of Fiji on Mon-Tue 1-2 Aug then moving off to SE then E, possibly re-intensifying near 30S 150W on Sun 7 Aug, with its trough affecting French Polynesia FP on Sun-Mon-Tue 7-8-9 Aug UTC.

Another trough MAY bud off near New Caledonia on Wed-Thu-Fri 10-11-12 Aug— but unsure at this stage, tune in again next week for an update on that.

SUBTROPICAL RIDGE STR
Subtropical ridge is expected to be strong this week, getting support from aloft. The high that is crossing NZ may stall for most of this week in North Tasman Sea. There should be some enhanced trade winds north of this high cell—affecting the Coral Sea on Mon 1 Aug and this affect spreading east to reach the Fiji area from Fri 5 to Tue 9 Aug – this little squash zone should be OK for sailing but not so good on divers, and should continue east onto Samoa, etc., next week.

Next High cell should cross Australian Bight Thu-Sat 4-6 Aug and eastern Australia Sun-Tue 7-9 Aug.

TASMAN SEA/NZ AREA
High hanging around northern and central areas until Thursday should bring frosts and fogs. There should be enough westerly flow over southern areas to just bring showers in the west, but a Roaring 40s trough on Thursday may bring a cold southerly change to all of NZ on Fri-Sat 5,6 August .

SAILING TO/FROM NORTHERN NZ.
Not a good week for sailing southwards.
OK for sailing northwards from Tues to Friday 2-5 Aug --- depending on how next week's trough near New Caledonia develops.

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