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

17 October 2009

BOBGRAM6 issued 18 Oct 2009

WEATHERGRAM
YOTREPS
Issued 18 October 2009
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 are in UTC unless otherwise stated.

We are now entering the migration season when several yachts shift in
the Southern Hemisphere from Tropical to middle latitudes.

There are still cyclones forming in the NW Pacific, LUPIT, and near
Mexico , RICK. There was burst of equatorial westerlies to north of
Papua New Guinea for much of last week, and an attempt at forming a TC
just north of Solomons, but nope, not yet. It looks as though South
Pacific will not be ready for a few weeks yet, maybe a month or more.

The ocean temperatures are consistent with an El Nino episode; the
Southern Oscillation index is hovering around neutral but starting to
lean in an El Nino direction. NIWA (NZ) and BoM (OZ) will be issuing
their cyclone outlook this week at
http://www.bom.gov.au/weather/cyclone/NatOutlookNotice.pdf
and (NIWA's Island Climate Update for Oct) at
http://www.niwa.co.nz/our-science/climate/publications/all/icu

South Pacific Convergence Zone SPCZ has been most active across the PNG/
Solomons doldrums area and then along 10S as far as Tokelau and then
between the Northern and Southern Cooks and across French Polynesia.
This location is further north and east than normal, as found in a El
Nino episode. Most likely the SPCZ will be drifting south over next few
weeks...should visit Samoa on 20 Oct, and Wallis/Futuna/northern Tonga
on 22-25 Oct, and Fiji/Southern Tonga on 26-28 Oct.

Winds in the Coral Sea have been strong SE last week and will be strong
SE until 24 Oct due to high pressure in the Tasman Sea. Anyone sailing
Vanuatu /New Caledonia to Australia this week are in for a bouncy rides.


CROSSING THE SUBTROPICS and HEADING FOR NZ

The thing to do when planning such a trip is to avoid squash zones
(where isobars are squeezed together as highs go by) and fronts. Try to
reach Northland between fronts - that means working out the average
timing of fronts reaching Northland. This is hard because weather
output is only good for a few days and your trip may take a week.
Usually if you deliberately arrange to go thru a front at 30S (where
they are usually weak) then that will give you a gap between fronts for
your landfall.

This week the subtropical high is the main features to watch............


The High forming offshore Sydney on Mon 19th is expected to move NE and
stall near Norfolk Island on 22 Oct. It will need to wait for a series
of fronts and troughs to make their way NE across eastern NZ, one on 19,
and another on 21 to 23 Oct --- so much of this week there will be
southerly winds over Northland (between Tasman high and the troughs to
the east).

However, after 23 Oct, that High is expected to poke its tongue out and
along 33S, followed by a NW flow -making a reasonable wind for landfall
in Northland for sailing from New Caledonia/Fiji/Tonga between 24 and 27
Oct. At this stage this window closes over Northland, for those coming
from Tonga anyway, around 28 Oct when next trough is expected to reach
Northland.

To work in with this window you will need to arrange to get to the
subtropical ridge (30-33S) by around 23 Oct.

For those in New Caledonia: there will be something of a squash zone of
the north side of that high when it is in the central Tasman Sea, so
you may need to sail SSW first when heading to NZ.

For those in NZ looking forward to the Coastal Classic:
Front reaching Auckland on Friday morning is the last in a series of
fronts and should be followed by that High then near Norfolk Island.
SO, at this stage, the outlook if for a stiff SW wind that may weaken
Friday night and briefly swing SE. EC model makes more of this SE at
present than do the other models, so it may be a fast race.

The current EC model deepens a low off Sydney on Sun 25 Oct --- this has
only a 30% chance of happening at this stage, so recheck.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

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