Issued 1 Apr 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 had a brief burst form the recent MJO or pulse of enhanced convection moving from North Australia to Coral Sea/South West Pacific. it has been hovering around 0.5 to 0.8 over past two weeks, but is likely to weaken over next two weeks. Still enough strength in it to be called a weak La Nina.
This MJO's arrival into the Southwest Pacific has brought a zone of near-gale near-equatorial NW winds from the Solomons to Fiji during the past week, enhancing the South pacific convergence zone SPCZ and triggering two tropical lows.
The first of these, Low 1, hovered near Fiji since Thursday and has produced extreme rainfall over western Viti Levu. It is expected to drift S and SW during the coming week hovering near Northland on Tue to Thu then drifting west to Norfolk/Lord Howe area , being directed by upper winds around an upper Low.
The second is currently over Vanuatu and expected to go SE to southwest of Fiji on Monday and northeast of Kermadecs on Tuesday then turn to the south and fade away.
The near-equatorial near-gale NW belt on the north side of the SPCZ should turn into a zone of squally westerly quarter winds all the way from Coral Sea to Tonga/Southern cooks by the end of this week - Islanders in this region need to be aware this is the opposite of normal , and several safe anchorages will become unsafe.
Kiribati and Tuvalu should miss these westerlies and just get NE/N/NW winds.
The SPCZ stretches all the way from Solomons to Fiji to Southern Cooks and should move northwards this week to be from Solomons to Tuvalu/Samoa to Southern Cooks by Saturday 7 April with squally NW winds on its northern side in places.
Galapagos to Marquesas: Still some tropical showers in the way between Galapagos and 5S as far west as 100W , along with weak west to NW winds. These are slowly fading, however this week it may be better to avoid the direct or 'more southern' route and motor up to about 1 degree North and catch the equatorial current west wards to around 125 W then going direct. Those who have already set off will need to get south to 6 South to find some useful easterly wind for sailing.
SUBTROPICAL RIDGE STR
Large High east of Chathams tonight should wander northeastwards this week to 35S south of French Polynesia by Sat 7 April.
A new High, High2, should stretch across Bass Strait on Wed and move over southern Tasman Sea on Thu and southern NZ on Good Friday to be over Chatham Islands on Sat 7 April. The track of this high will help mould the track of Low1 into the Tasman Sea.
TASMAN SEA/NZ AREA
Weather is dominated by Low1 and High2 during this week and into Easter.
Easterlies for Easter for the North Island.
The easterly winds and frontal rain around Low 1 should have its greatest impact over the North island from Tue to Wed. The E to NE winds in the squash zone of High2 are likely to build on Good Friday and last until Easter Sunday, when a weak trough moving onto the South Island helps the isobars to spread out again.
Things may work out that Thursday is the day between wind blasts -- so it may be an OK day to start the annual Auckland to Tauranga Yacht Race. But Friday's likely increasing E/NE wind in Bay of Plenty may also be upsetting near the RENA reef, so race participants should arrange checks for latest updates.