BOBGRAM7 issued 4 July 2010

WEATHERGRAM
YOTREPS
Issued 4 July 2010
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.

Galapagos to Marquesas: It seems this week that the direct route using
the current near 4South is NOT any faster than the alternative route
using the strong west-going current at around 2 degrees North from 100
to 120W. If you do decide to take the northern route you have to get
away for the east-going current at the equator, and you will likely
experience some squally showers.

TROPICS
South Pacific Convergence zone SPCZ is reasonably quiet this week, and
is mainly in the northern Coral Sea and northern Vanuatu and from there
along 10S towards Tokelau and Northern Cooks. There is an interesting
dry slot of sinking air from Fiji to Southern Cooks, and another around
northern Australia.
Due to High pressures that are now blocked over southern Australia there
is a zone of enhanced trade winds in the Western Coral Sea and around
the north end of Queensland. This should ease after 7 July but isn't
going to go away this week.

SUBTROPICAL RIDGE: STR
High to east of NZ today Sun 4 July is set to move steadily along 30S
and fade on 5 July. Another associated High should expand at 45S -50S
and this High fades This High should then move NE and reach 40S to south
of French Polynesia around Fri 9 July, with a squash zone of enhanced
trade winds on its northern side.
Next high upstream is stalled over South Australia but should be able to
send a cell across Tasmania on 8 July, South Tasman Sea on 9 July, and
South Island on 10-11 July.

TASMAN/NZ
This week the NZ region will be dominated by a large slow-moving low.
It isn't expected to ingest any cold polar air until 9 -10 July and by
then should be mostly off to east of NZ. The centre is expected to
track east along 33S to 180 and then southeast, so that most of its wind
and rain should stay out to sea, but Gisborne and Hawke's bay are in for
steady rain from Monday to Wednesday. The SE winds associated with this
low should cover northern NI tonight/Monday and central/southern North
island on Tuesday and Wednesday 6-7 July.

The low should be far enough away to allow reasonable sailing to the
north again by Thu 8 July. There is likely to be a left-over trough
between NZ and Fiji and this may activate early next week, so updates
will be needed.

As for sailing from Tonga to NZ, well : there may be a reasonable voyage
afte the low has gone, starting around 9 July, but you will need to be
prepared to sail through a trough.

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