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

11 April 2011

BOBGRAM7 issued 10 April 2011

Issued 10 April 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.

Now that the equinox has faded away, the next thing to watch in this new
'meteorological' year is the jetstream over Tibet. The subtropical jet
in the northern hemisphere is now near the Himalayas so no one will be
climbing Everest yet- but, by mid May, this jet should get further
north and a brief Everest climbing season should occur before the Asian
monsoon kicks in.

La NINA is making a rebound as isobars lower over North Australia. The
Southern Oscillation Index 30day running mean moved from a low of 1.85
on 25 March to 2.51 on 9 April.

In our part of the world the South Pacific Convergence Zone is taking on
a position towards the south end of its range and is defined in a long
stretch from northern Australia across the Coral Sea and Southern
Vanuatu to south of Fiji and then off to the southeast. There is a
tropical depression within this system - tonight it is east of Tanna and
west of Fiji. This system is expected to go SE and deepen to below
1000hPa by Wed 13 April when it is well off to SE of Raoul Island.

A Madden-Julian-Oscillation MJO has been activating convection over
northern Australia recently and is wandering into the west pacific. It
seems to be having more impact in the Northern hemisphere rather than
the Coral Sea.

A typical autumnal anticyclone is crossing central New Zealand and
should move off to east from Wed 13 April.
Another High is expected to wander over Tasmania on Fri/Sat 15/16 April
and then cross central NZ on Sun/Mon 17/18.

Between the highs are troughs and lows. Low should deepen just northeast
of Tasmania on Tue 12 April and then weaken and stretch out into a
trough that is likely to move from SW to NE across NZ on Wed 13 to Fri
15 April, followed by a southerly change.

Anyone planning an early get-away from Northland to the tropics may
takeoff over next few days OK; so long they avoid that low from Tanna.
NE to NW flow and a passing trough make for bad days from Wed 13 to Fri
15 April. The SW to SE flow on Sat/Sun 16/17 April make for a few good
days, but these are likely to be quickly followed by an E/NE flow on 18
April onwards, so may as well wait for next window and forget taking off
this week.

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