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

08 November 2008

BOBGRAM7 issued 9 Nov 2008

Issued 9 Nov 2008
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos, these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates below are given in UTC unless otherwise stated.

Monsoon looks less active than last week but did produce a TC MYSAK.
There is no sign of any equatorial westerlies and no sign of a Madden
Julian Oscillation so looking like it will be a few weeks, maybe more
than a month before we start seeing cyclone activity in this part of the
world. Wow, TC Paloma moving in from the south onto Cuba shows there
is plenty of energy available over there.

South Pacific convergence Zone SPCZ has cleared away from Coral Sea
during past week and is now weak from Tuvalu to Samoa to Northern Cooks.
The active thundery area which visited Fiji Wednesday and Tonga /Minerva
/Kermadecs over past few days and is now over the Niue area is really
caused by an upper trough sitting on top of the tropical easterlies.
This bunch of cold air aloft is confirmed by the hail and whirlwinds in
the showers that visited Fiji last Wednesday. And that's why the winds
have been so slack south of Fiji/Tonga and NZ last week. Anyway the
upper trough has "eaten downwards" and formed a slack surface low near
Kermadecs as picked in the last Weathergram. Yippee, it is good to see
the physics working-we had a lot of cold air flood over NZ last week and
its arrival in the subtropics threw the global weather models in a tizzy
for a few days - their grip on the real world seems to have returned

There is a slack variable flow between Fiji /Tonga and NZ with the
subtropical ridge now shifted to around 40S.
Another upper trough is likely to form another slack surface low near
Lord Howe Island on the front passing the area Sunday/Monday. This will
stall the front so that it sits between New Caledonia and Queensland for
the remainder of the week, fading away. That Low near Kermadecs has a
squash zone between it and the intense subtropical ridge that is near
40S. This squash zone is near 30S and reaches a peak on Monday,
probably worth avoiding unless you like roller coasters Between the
Kermadecs and Lord Howe Lows is a zone of light winds for much of this

Front in the Tasman Sea today Sunday is expected to fade over the South
Island on Monday, allowing a new HIGH to form in the central and
southern Tasman Sea on Tuesday and this crosses central NZ on Thursday.

Next front should have more penetration, getting across Northland late
16 or early 17 Nov. Avoid arriving in Opua with or just after this
front. At this stage 18 to 22 Nov are all looking OK days for making
landfall--- try and arrange to go thru this front when it is at 30S ,
say on 17-18 Nov or soon after. From those dates and your vessel speed
you can work out when it may be best to depart Fiji or Tonga or Minerva.
Looks like a breeze good enough for sailing should return to these
places around Wednesday 12 or Thursday 13 Nov, maybe - but the lights
winds on the way will mean some motoring.

I am attending to a MetService display at the Royal Show from Tue 11 to
Fri 14 inclusive, so unavailable this week. Will check email on Sat 15,
then unavailable again from Sunday 16 to Friday 21 Nov, attending a
conference in Greymouth, back on deck Sat 22 Nov. So happy sailing
while I'm away.

The terms used are more fully explained in the METSERVICE Yacht Pack.
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