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

02 June 2013

BOBGRAM issued 2 June 2013

Issued 02 June 2013
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.

Background influences
The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) is based on the standardised difference in the barometer readings between Tahiti and Darwin. It sums up the weather pattern over the South Pacific as one number.
SOI rose to over plus 1 briefly in early April and dropped to minus 0.39 in early May and bounced back into the positive in May, and reached plus 0.83 on 31 May. So the signal coming from the Atmosphere has been erratic and at present is tending towards La Nina.

The Ocean: Sea surface temperatures SST across the equatorial Pacific may be thought of as a thermostat for the planetary weather engine. The warmer the sea the quicker it evaporates, tossing water vapour into the air, and when this vapour rises then it cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet so its abnormalities tend to influence changes in clouds along the equator and these in turn tweak the latitude zones of weather around the planet.

In the past month there has been a growing area of cooler than normal conditions over the eastern equatorial Pacific. This is possibly a sign of a trend towards La Nina conditions, but we still do not have enough evidence to say this trend will continue

ITCZ and Monsoon
ITCZ is strong across the Pacific. Monsoon has arrived in Kerala, SW India, on 1 June. It is on time and seems to be more active than normal at this stage. It is expected to reach Delhi by 29 June. Also active convection for Sea of Bengal.
This marks the end of the 2013 Everest climbing season (with 8 fatalities). Everest was first climbed on 29 May 1953 by Tenzing and Hillary, and news of this was made public on 2 June 1953 at QEII coronation 60 years ago today. We in NZ are having a public holiday on Monday and you should too!

South Pacific Convergence Zone SPCZ
The SPCZ moved southwards over Vanuatu and Fiji last week, resulting in the Low that is tonight near 28S 178W and moving off the SE reaching 44S 150W by 05 0000UTC. This Low has drained a lot of convective energy from the tropics.
This week the SPCZ is weak and recovering as scattered lumps of convection mainly along 10S.

Sub-tropical Ridge STR
The next HIGH in the STR is currently in the Australian Bight and is expected to cross eastern Australia on Monday and Tuesday and then the Tasman Sea on Wednesday and Thursday reaching North Island on Friday 7 June.

Roaring 40s and New Zealand
This week the STR is weak in the NZ longitudes and this allows the trough crossing NZ to blossom into a large Low over the North Island by Tuesday. Avoid.

Route weather picks
Galapagos to Marquesas: Good to go this week. We have light to moderate South to southeast winds over Galapagos and moderate trade winds trade winds from 2S onwards.

NZ to the Tropics.
Wait for the trough to move away from the North Island. There may still be some squally SW winds around on Wednesday, but Thursday may be good to go. Friday/Saturday/Sunday could have winds too light in the passing high. Next front to reach Northland is likely on Monday/Tuesday 10/11 June, closing the window.
So the best day to go from Northland this week is Thursday.

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