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

26 July 2008

BOBGRAM7 issued 27 July 2008

WEATHERGRAM
YOTREPS
Issued 27 July 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

TROPICS
South Pacific Convergence Zone SPCZ is hugging the 10 South latitude from Solomons to Tuvalu/Tokelau, and was also reasonably active last week from Northern Cooks to French Polynesia FP - it should relax over FP this week.

I made a typo last week saying "There are Northeast to easterly winds on its northern side and southwest winds on its southern side."  That should have been SOUTHEAST winds on its southern side - the ordinary trade winds-but they are under strength at present, and the SUNTROPICAL RIDGE is well NORTH of its normal winter position (of 25South) with one centre at 20S over the southern Cooks and another forming near New Caledonia by Friday. The High over Southern Cooks is expected to migrate to 35S 140E by the end of this week. 

The reason for this deviation from norm is that COLD POOLS are forming aloft over the Tasman Sea --- These cold pools are diverting the subtropical ridge to the north.   This is knocking the main latitude belt of the 20 knot trade winds to between 10 and 20 South, and opening places such as New Caledonia to occasional frontal passages.

The clouds and trough for the next of these frontal passages are already gathering offshore of Brisbane.   The northern end of this frontal zone is expected to cross New Caledonia on Monday and Fiji/NZ on Tue/Wed.  Avoid.

TASMAN/NZ AREA
Last week's low from the Queensland area was "NO ORDINARY STORM" and deepened to 963 hPa as it crossed Northland yesterday, moving quickly east/southeast.

This week's low, forming near Lord Howe Island on Monday, is expected to deepen to 983 by the time it reaches New Plymouth area on Wednesday, and by then to be more wide-spread than last week's low... but it is likely to be blocked so that it takes its time crossing central and southern NZ on Wed Thu and Friday, followed by squally west or Southwesterlies over the weekend of 2/3 Aug.  Avoid.

This closes down any comfortable sailing around the Tasman Sea/NZ area for another week or more.

The terms used here are more fully explained in the METSERVICE Yacht Pack.   Feedback to bob.mcdavitt@metservice.com

19 July 2008

BOBGRAM7 issued 20 July 2007

WEATHERGRAM
YOTREPS
Issued 20 July 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

TROPICS
The South Pacific Convergence Zone is hugging 10 South latitude from
Solomons to southern Tuvalu/Wallis - Futuna to Samoa, and is indistinct
further east, in the region between Southern Cooks and French Polynesia.
There are Northeast to easterly winds on its northern side and southwest
winds on its southern side.
Not much variation in this theme this week, except for a development
between Queensland and New Caledonia-a LOW is expected to form offshore
of Queensland on Wednesday 23 July. EC model picks this low to go east
past New Caledonia on Fri 25 July then southeast past Raoul Island over
the weekend. GFS model picks that the low may deepen to 985 hPa near
Norfolk Island around 12ooUTC Friday 25 July and then skirt past NE
parts of NZ over the weekend. There will be a gale force squash zone of
easterly winds on the southern side of this low, so AVOID, please.


MID LAITUDES
The best day of the week for sailing around NZ will be Monday 21 July as
a weak ridge passes by.

A LOW deepening to below 970 hPa to east of Tasmania on 21/22 July has
its cold front crossing NZ on 22 July followed by the LOW and its
squalls on 22/23 July and then a strong cold southerly flow on 23/24/35
July in time for that LOW from near Queensland to do a fly-by over the
weekend. So it's too unsettled for any voyaging to or from NZ from Tues
22 until at least the end of the month.

A HIGH in the Aussie Bight on Monday is expected to move east across
Victoria on 22/23/24 July and into South Tasman Sea and south of NZ on
24/25 July. This HIGH feeds cold southerly winds onto NZ, and there will
be a squash zone of enhanced easterly winds on its northern side
interacting with that low from the Queensland coast.

NOTE: I am on leave until 28 July but will be checking my email this
weekend 26/27 July.

The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

13 July 2008

BOBGRAM 7issued 13 July 2008

 

WEATHERGRAM

YOTREPS

Issued 13 July 2008 NZST

Bob McDavitt's ideas for South Pacific sailing weather.

(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).

 

 

Just a quick weathergram this week—I have people staying here for teh weekend and limited time to look at the weather.

 

 

TROPICS

The South Pacific Convergence Zone is increasing in activity especially over eastern Solomons and extends from there to Wallis /Futuna and then southeast across the Niue/Southern Cooks area...the eastern section of the zone is likely to spread north onto Samoa this week.

 

 

MID LAITUDES

Not a good week for sailing across the Tasman Sea. We have disturbed weather in the Tasman - with a front reaching NZ on Tuesday and a Low and front on Friday and Saturday.

 

NOTE:  I am on leave from on 14 and 15 July and then again from 18 to 25 July so next weathergram may be delayed a while and I’ll be unable to do any voyage forecasts during that time.

 

The terms used here are more fully explained in the METSERVICE Yacht Pack.   Feedback to bob.mcdavitt@metservice.com

 

 

05 July 2008

BOBGRAM7 issued 6 July 2008

WEATHERGRAM
YOTREPS
Issued 6 July 2008 NZST
Bob McDavitt's ideas for South Pacific sailing weather.
(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).

Galapagos to Marquesas: For the late comers: Head direct for 4S 96E
then go straight. This will avoid the strong east-going current and use
the winds best: winds are SE over Galapagos and turn easterly to west of
110E. Be on watch for a few tropic squalls between 120W and Marquesas

TROPICS
The South Pacific Convergence Zone is going thru a quiet time now. It
starts the weak active along a zone from Papua New Guinea across
Solomons and northern Vanuatu to Fiji and Niue and to the southeast.
The section east of the dateline is expected to be active on Mon UTC and
then fade away from Tuesday UTC. There is another branch of the SPCZ
near10S from Tokelau to Marquesas. This is more properly known as a
shear line. It has lighter easterlies to its north and strong easterlies
to its south, anyway it is breeding thunderstorms so be wary there.

A mid latitude low is expected to deepen in the cold air that is being
shunted into the subtropics--- near 33S 155W on Thu or Fri UTC. This
will activate the SPCZ between Tahiti and Southern Cooks into a trough
with squally showers.

SUBTROPICAL RIDGE

HIGH above 1028 crossing the central Tasman Sea along 40S next few days
and NZ on Wed 9 July UTC will enhance the trade winds to north of it
into a squash zone. This Squash zone should cross New Caledonia on 7-8
July and over Fiji-Tonga-Niue from 9 to 13 July UTC. Take care.

MID LAITUDES
A cold pool moved onto the North Island this weekend in tandem with a
deepening surface low off the east coast- bringing the coldest day of
the winter so far on Saturday, with snow and ice closing many roads.
It'll be a hard winter storm to beat, perhaps this winter's nadir.

Weather window is ripe early this week for heading from NZ to Fiji/Tonga
and for coming the other way as well.

One last southerly wind change with showers rippling along NZ east coast
on Monday, then a few days with light winds- frosty morning and sunny
day- from a passing HIGH.

Next front /trough should form off the Australian Coast on Tue 8 July
UTC and reach the South Island on Friday 11 July UTC preceded by NW
winds - good rain for the hydro lakes- then the North Island on Sat 12
July UTC followed by a westerly flow.

The next front, due over the North Island on 14 July may have strong
wind and rain, and will be followed by SW winds. This one is worth
avoiding; one of the computer models is developing a LOW with it.

NOTE: I am on leave from 9 to 15 July, so next weathergram may be
delayed a while and I'll be unable to do any voyage forecasts during
that time.

The terms used here are more fully explained in the METSERVICE Yacht
Pack. Feedback to bob.mcdavitt@metservice.com

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