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

26 October 2008

BOBGRAM7 issued 26 Oct 2008

WEATHERGRAM
YOTREPS
Issued 26 Oct 2008
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 below are given in UTC unless otherwise stated.

TROPICS

Nov to April is the period described as Cyclone season for the South
Pacific. Most Insurance companies do not pay out on any storm damage to
yachts in the South Pacific during this period, so that's why early
November triggers a migration of yachts out from Tonga and Fiji.
Climatologists looking at the coming cyclone season are expecting, on
the basis of the sea surface temperature trends, that it should be
average (8 to 10 named systems) with a slight drop in risk east of the
date line and a slight increase in risk for the Tasman Sea/NZ area.
Normally the first cyclone appears soon after equatorial westerlies
arrive over the Papua New Guinea/Solomons area... the Monsoon is active
over Indonesia but there is no sign of these westerlies, so my pick is
that the first cyclone is something like six weeks or more away.

South Pacific convergence Zone has been stationed from Papua New Guinea
across Coral Sea to Vanuatu/ New Caledonia in past week and
intermingling with a mid-latitude trough that crossed New Zealand.
Another branch has been coming and going in the Samoa area.

Not much change expected in the SPCZ this coming week, but some
activity is expected between Tuvalu and Vanuatu early this week.

SUBTROPICS

I received an email from a yacht near the dateline and 30S on Saturday
reporting 30 knot westerlies and 8 metre swells. So my weather gram
last Tuesday was worthwhile following. The trough is still lingering
over Kermadecs today and may bring some squalls to the Minerva area on
Tuesday or Wednesday.

Subtropical ridge is likely to be draped along 30/33S between 160W and
160E all this week until Sun 2 Nov. Slack winds and left over clouds
in this zone, but SE winds are likely to often be over 20 knots between
20 and 24 South, including Minerva reef.

TASMAN SEA / NZ AREA and the All Points Rally

With the annual yachting migration about to occur there is also the All
Points to Opua Rally of the Island Cruising Association, mainly from
Pangaimotu (Tonga)/Musket Cove (Fiji)/Vila (Vanuatu)/Isle des Pins (New
Caledonia) to Opua, starting 1/2/3 Nov.

There isn't much dramatic happening in the weather, but anyone leaving
Fiji/Tonga before Wednesday will likely need to go on squall watch
during Tuesday/Wednesday near 22 to 24South.

Early next week, around Monday 3 November, as a front crosses the North
Island, a small Low is likely to form on this front. This Low then
likely grows and fades when it is east of the North Island on 4 to 6
November... making for several days of SW flow over Northland.

So maybe your strategy will be to time your arrival in Opua after this
SW - or maybe sail so you take them as side-on as you can. It's hard to
tell this far out, but current indications are that the SW winds near
Opua are likely to be strongest 4-6 Nov.

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

20 October 2008

BOBGRAM7 SPECIAL issued 21 Oct 2008

WEATHERGRAM
YOTREPS
Issued 21 Oct 2008 EXTRA ADDITION PLEASE READ
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 below are given in UTC unless otherwise stated.

TONGA to NZ update

Computer models are now converging with their output handling the LOW
that is now forming in the Tasman Sea. It is expected to deepen as it
crosses northern NZ on Friday and east of the North Island on Saturday.
There is a high likelihood of westerly gales at 30S from about Norfolk
to Kermadecs on Sat 25th.

SO if you are trying to get to 30S by 24 Oct as I suggested in my last
Weathergram then please ABORT. If you know someone who has sailed off
please pass this on. That strategy for getting from Tonga to NZ WORKS
WITH FRONTS but it DOESN'T WORK when fronts have LOWS of this size
attached to them. Time now to return to port and await the next
window... the front associated with this low is expected to clear off
southern Tonga on Mon 27 Oct so next window may well be Tuesday 29 Oct.

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

18 October 2008

BOBGRAM7 issued 19 Oct 2008

WEATHERGRAM
YOTREPS
Issued 19 Oct 2008
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 below are given in UTC unless otherwise stated.

TROPICS The South pacific Convergence Zone, SPCZ, went through a period
of activation in the Coral Sea last week. This was induced by a passing
of an upper level trough and the corresponding 'blob' went over Loyalty
Islands on Friday, to south of Fiji on Saturday and is now weakening
over Minerva reef. The latest Quikscat imagery conforms a reflection of
this trough at surface level, with a zone of northerly winds and
clearing weather passing over southern Tonga today and Monday (UTC).
May be useful for Island hopping.

The SPCZ this week is expected to mainly extend from northern Coral Sea
to Vanuatu to south of Fiji and occasionally to Southern Tonga, with
another branch from Tokelau to Northern Cooks

For the Port2Port this week there is an unavoidable squash zone in the
Coral Sea, it marks is fed by a rather weak HIGH cell crossing the
Tasman Sea from 19 to 21 Oct. Another HIGH is likely to cross the Tasman
Sea from 23 to 27 oct, and its squash zone may weaken from 26 Oct as the
SPCZ goes through another period of activation.

NZ/TASMAN SEA
The main challenge this week comes from a LOW that is likely to form
near Lord Howe Island on 21 Oct. By the way, this low is expected to
form between highs in the subtropical ridge, a standard pattern. The
conflicting densities of air feeding into this low from the warm moist
north and the cooler south is not being handled well by the computer
models. The main model that you may have access to in your GRIB files
is the GFS, and it and the NOGAPS model deepen this low and take it
across the North Island on Friday, just in time for our COASTAL CLASSIC
from Auckland to Bay of Islands. The EC and Canadian models do not
deepen it so much and may track across the north of Northland, a
different outcome. At this stage the best pick is somewhere in-between
and nothing more definite can be written until the models start to
converge.

One thing that can be said about this low is that it will be forming
whilst a front, today in the South Tasman Sea, moves north across New
Zealand. That front is followed by some grunty swell from the southern
Ocean and the LOW will help enhance that swell, especially along the
western part of the Tasman Sea along the Australian coast as far north
as Brisbane to Lord Howe on Thursday, and also on the western side of
the Low as it crosses whichever part of northern NZ it does around 24
/25 Oct. Avoid this swell.


Tonga to NZ
I like the idea of taking on a front at around 30S--- they are weak at
that latitude and there plenty of ocean to play with. Fronts this time
of the year are about 5 to 7 days apart on average crossing NZ, and the
voyage, over 1000nm will take you over a week so meeting a front is
unavoidable. Doing so mid-way maximises your chances of making landfall
in NZ "between fronts". I think this is a better strategy for a
cruising yacht than attempting to make landfall in NZ as a front is
approaching (but some may prefer this).

Anyway: this week THE FRONT associated with that Tasman Low is
expected to be crossing that magic point-pretty well half-way between
Raoul Island and 30S 180- on 24 Oct. So my best idea is that you depart
from where you are in Tonga to reach that point around 24 Oct and head
sufficiently off to the west to allow for the SW winds that will follow
that front, and the SW winds that will be on the western side that that
low, and you should have a reasonable voyage. As for the swell on the
western side of that Low, you will meet it near 30 to 35S over the
weekend, but by then it will be around 3m and on the decline /long
period, so not too bad.

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

12 October 2008

BOBGRAM7 issued 12 Oct 2008

WEATHERGRAM
YOTREPS
Issued 12 Oct 2008
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 below are given in UTC unless otherwise stated.

October's full moon is on the 15th - good for cruising. During the
following week, induced by the spring tides a few days after that full
moon, there will be a few nights where the annual PALOLO RISING (in Fiji
the BALOLO RISING) may occur when coral worms spawn. Worth checking
out, ask the locals. And the New Moon on the 29th is marked with the
Hindu Festival of Lights - rather dark for cruising.

The annual analysis paralysis season is about to start as cruisers in
Tonga gather all their ideas together to try and pick the 'best' time to
leave for NZ. My ideas will be just part of this, and I have no ideas
beyond 24 Oct at this stage.

TROPICS The South pacific Convergence Zone, SPCZ, extends from Solomons/
Coral Sea to Wallis/Futuna to central Tonga to a LOW that has formed
south of Niue. - There is a weaker branch from Samoa to Northern Cooks.
That Low south of Niue is expected to fade where it is on Monday. The
area should remain troughy with a squash zone near 30S 150 to 170W as a
big fat high moves east of NZ and bananas-around it at 40S, 14th to 16th
Oct. Avoid this squash zone - but is should generate some useful swell
for surfers in Bay of Plenty/ Bay of Islands for 18/19 Oct (this isn't
being picked by the computers but I think it's a good possibility). The
troughy area should reforms that Low near 30S 160W on 16th as that high
moves further East, and the LOW should be captured by the next
mid-latitude trough and go off to the SE-associated trough should bother
Niue on 15 Oct and may bother Southern cooks on 16-17 oct. Take care.

SPCZ is moving south across Coral Sea and computers are picking it may
develop a trough visiting New Caledonia 15 to 17 Oct and Southern Tonga
17 to 19 Oct. Squally showers, and appears in those GRIB files as a
deceptive zone of light variable winds. Avoid.

SUBTROPICS /NZ/TASMAN SEA
One migratory HIGH is moving along 40S across NZ on 12-13 Oct and then
off to the east 14-17 Oct. Its squash zone is being focused at 30S by
that troughy region south of Niue.

Between Highs, a trough should broaden over NZ 16-18 Oct.

Next subtropical HIGH is expected to form in Tasman Sea 16 oct and move
northeast and fade over Lord Howe area 19 Oct-it is a brief one, but
good for Tasman sea sailing.

Next trough broadens over NZ area 20-24 Oct and since the next HIGH
seems likely to form in the Tasman Sea at 40S , that would suggest a
cold southerly over NZ on 23-24 Oct. Avoid.

Sailing to NZ? Try and arrange your arrival to be WITH the HIGHs
(13-15, 18-19, 24-26 Oct).

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

05 October 2008

BOBGRAM7 issued 5 Oct 2008

WEATHERGRAM
YOTREPS
Issued 5 Oct 2008 NZDT
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 below are given in UTC unless otherwise stated.

Addendum to those comments last week about the coming cyclone sea:
Outlook is for neither El Nino nor La Nina, so neutral territory.
Previous years in neutral territory show a REDUCED RISK of cyclones
around Northern Cooks and French Polynesia. For NZ there is an INCREASED
RISK. In-between these places a normal cyclone year may be expected,
and that included the Coral Sea/ Vanuatu area.

I'll be brief this week because it is late Sunday after a weekend of
sailing fro me.

TROPICS The South pacific Convergence Zone, SPCZ, extends from Solomons
to Tuvalu - this branch may move slowly southwards during the coming
week possibly reaching central/southern Vanuatu to Fiji by 15-17
October. Avoid. Another weaker branch of SPCZ extends from Tokelau
across Northern Cooks towards Marquesas. The northern extension of a
mid-latitude front was noticeable from Vanuatu to Fiji and thence to the
Southeast last week (even had some gale warnings), but isn't likely to
appear this week.

Southeast trade winds cover the entire South Pacific-no sign of any
westerly winds yet. Since the subtropics are well marked between 30 and
35S these trade winds are generally strongest along 20S.

SUBTROPICS
One migratory HIGH is moving along 30S, and centred south of Fiji to
French Polynesia on Monday should fade by Wednesday. Next HIGH is
likely to appear in western Tasman Sea on 9 Oct and cross the North
Island along 35S on 11-12 Oct and fade away by 14 Oct.

North of these HIGHs, there will be enhanced east to southeast winds at
20 S.

TASMAN/NZ
Front crossing NZ on Monday Tuesday 6/7 Oct is likely to also bring a
LOW crossing the South Island. Avoid. Severe westerly winds should
follow this front on Wednesday 8 Oct (avoid) followed by a easing
anticyclonic SW flow on Thu 9 to Sun 12 (OK). Spring -type weather.

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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