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

29 January 2011

BOBGRAM7 issued 30 Jan 2011

Issued 30 January 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.

La NINA is still strong. Average atmospheric SOI over 30 days ending 27
Jan is 1.87 (a drop of 0.54 since 21 Jan). .

WILMA followed its expected track and sideswiped Northland and eastern
Bay of Plenty Friday night/Saturday.

ANTHONY lost its top clouds when it re-curved a few days ago, but has
managed to grow some more and get re-named , it now weakening again and
should make landfall between Townsville and Mackay overnight tonight/
around 1am Monday local time.

Another tropical low, just named YASI, is now deepening as it approaches
northern Vanuatu from the east. It is expected to become a major
system and keep going west, gathering energy over the Coral Sea. At
this stage, it is on track to make landfall between Townsville and
Cairns on Thursday 3 Feb UTC. Avoid.

YASI is likely to end this period that has allowed the formation of a
cluster of cyclones, and gradually allow a return of trade winds to the
South Pacific around 5/6 Feb. The South Pacific Convergence Zone SPCZ
has been broken into pieces over past few weeks and should start
reforming along 10 South next week.

High/ridge has shifted to 35S in the North Tasman Sea by a shift
northwards of cold air from the roaring 40s. The front responsible for
this northern shift crossed South Island last Friday in time to capture
WILMA and kick it southeastwards, thus limiting its impact on NZ

This high cell is likely to be held in place by an upper ridge until the
5/6 Feb weekend, when it should migrate to east of North Island.

So, it looks like a week of disturbed westerly flow over NZ, with fronts
weakening over the South Island on Monday, Tuesday/Wednesday and Friday.
These fronts may each bring a period of NW gales to eastern districts
and heavy rain about and west of the South Island divide.

Next high is likely to form in Aussie Bight around Sat 5 Feb and move
into Tasman Sea around Sun 6 Feb (Waitangi Day holiday in NZ), pushing a
substantial cold front as S/SW change over NZ. Avoid this cold front.

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