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

25 March 2012

BOBGRAM issued 26 March 2012

Issued 26 Mar 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.

Apologies for delayed write-up this week, I was busy on Sunday evening.

The MJO or pulse of enhanced convection that has been moving towards Coral Sea over past few weeks has peaked and is now on its way out. The next pulse will be too late to do much in the way of developing South pacific cyclones, so the next ten days is probably the last chance for something to form to mark the end of the cyclone season.

Pressures in the Coral Sea have been falling and continue to fall—the South Pacific Convergence Zone SPCZ has branches across middle and northern Tasman Sea and computer models are showing that a tropical LOW may form over FIJI on Tuesday and deepen for a few days as it wanders towards Tonga (in mourning with Kings Funeral) and then weaken on weekend31 March/1 April.

Of more interest is the tropical low that may form over eastern end of Solomons around Thurs/Fri 29/30 March and deepen, possibly into a cyclone, around Vanuatu on Sat/Sun/Mon 30/31/1 and then this should move into the Tasman Sea/NZ area as a significantly large storm on Mon/Tue/Wed 2/3/4/5 April – too far away to be sure of its track and development at this stage, but something to consider for any pre-Easter sailing around NZ.

The main branch of the SPCZ stretches from Tuvalu to Southern cooks and terminates in a LOW near 30S 160W. This Low should move off to SE around Fri/Sat/Sun 30/31 March/ 1 April.

Galapagos to Marquesas: Slowly becoming possible. The ITCZ International Convergence Zone did a jump to near 5S in past few weeks between 170W and 90W – this sometime happen around the equinox when the sun is directly overhead there. Well as we move away from equinox the ITCZ returns to normal. At present CZ is directly over Galapagos, so may as well wait another few days for the CZ to drift to its normal position in the north.

High stretching from Aussie Bight across Victoria/New South Wales to Mid Tasman is expected to move around south end of NZ on Wed/Thu 28/29 March and Chathams Islands on Fri/Sat 30/31 March, preceded by a southerly change and bringing autumnal weather.

Weather is dominated by the passing High this week. Keep an eye on the low that is expected to form near Vanuatu by late in the week, as the squash zone between that and the high near NZ is likely to dominate next week's weather over New Zealand as Easter approaches.
The terms used are more fully explained in the METSERVICE Yacht Pack.
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