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

26 June 2011

BOBGRAM7 issued 26 June 2011

WEATHERGRAM
YOTREPS
Issued 26 June 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.

TROPICS
Southern Oscillation Index SOI is in neutral territory, staying between 0.26 on 19 June and 0.29 on 26 June.

Galapagos to Marquesas: Slight change. The seas around Galapagos are now getting slightly warmer than normal and the SSE winds there are slightly less than normal. It is making more sense to get west as soon as possible and seek the better winds west of 95W. So just one way point may be all that's needed now…somewhere near 6S 132W and then head for Marquesas. There are some tropical showers 3-5S at 130w.

As for the Panama to Galapagos leg: it is looking better than last week, the ITCZ seems to be a little more north in that area, so it is now a route with light winds, and may be some tail winds on Monday.

South Pacific Convergence Zone SPCZ has reactivated and is mainly draped from Solomons, across Vanuatu and Fiji then to the southeast. There are also some convergence zones over Tuvalu and Tokelau and, unusually, between 2 to 5S from 130w to 160W.

This coming week the SPCZ should stay in much the same place in Coral Sea/Vanuatu, but may drift to north of Fiji with part of it drifting from the south onto Tonga by end of week - and linking with a low or trough that may form around the Kermadecs.

SUBTROPICAL RIDGE STR
New High is taking its time over Australia along 35S, and pushing a tongue across northern Tasman Sea along 30S… this is enhancing the trade winds in Coral Sea into a squash Zone. Fiji MetService has issued a gale warning on this area for tonight.

This high is expected to finally get into the Tasman Sea east of Tasmania at 40S by Tuesday 28 June. This will make for a squash zone between it and a Low that is then expected to deepen in the cold air over North Island. There will be strong SW winds /rough seas / heavy swells in this squash zone and these will travel north and east reaching the area between North Island and Fiji/Tonga on wed/Thu June then ease and move off to the east. Anyone travelling this route may wish to consider waiting until after Thursday for this stretch of ocean to settle.

The high may fade away this weekend with its remnants crossing southern or central NZ, bring frosty air. By early July, a new high cell should form east of NZ along 40S. There will still be a squash zone on the high's northern side: this is likely to re-intensify in Coral Sea over the weekend, but may ease further east.

TASMAN SEA/NZ AREA
The secondary low that crossed the North Island this weekend was cold enough to bring 10cm snow to Ruapehu. There's another of these lows likely to deepen over the North Island on Tuesday—strong cold southerlies for Cook Strait / southern North Island (in squash zone between high and low) and another dose of snow for Ruapehu, especially on Wednesday. This is a typical "Old man southerly", but may be notable as it's the first we have had in a long while.

SAILING TO/FROM NORTHERN NZ.

It may be more comfortable to let this week's Low go first.

As for the next low that may form around Kermadecs early in July: well, still too far away to resolve much detail, but it may be easier to go clockwise around (travelling north) than this Thursday's low, and is NOT expected to have as much strong wind/rough sea/heavy swell.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

19 June 2011

BOBGRAM7 issued 19 June 2011

WEATHERGRAM
YOTREPS
Issued 19 June 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.


TROPICS
SOI is in neutral territory, in past few weeks its 30day running mean has risen from 0.18 on 5 June to 0.73 on 12 June then fallen back to 0.26 on 19 June.

Monsoon is making reasonably average progress over India. There may be a tropical cyclone forming east of Philippines and this feature is expected to go NW and make landfall on China but, at this stage, it isn't expected to become intense.

Galapagos to Marquesas: More of the same. Avoid the Equatorial current. Dive south to around 5S 100W and then head almost due west to 7S 133W and then head for landfall. There are some tropical showers north of Marquesas from 135 to 145W mainly along 3S, but these will probably not affect the voyage. But if you are attempting the Panama to Galapagos leg, be aware that ITCZ is strong to south of Panama along around 5N.
South Pacific Convergence Zone SPCZ is having a quite time — some disorganised slumps east of the dateline, and a more organised line stretching from south of Solomons across Vanuatu then SE to south of Fiji where it merges with a mid-latitude trough/front which is travelling eastwards. This trough may trigger the development of a low to south of French Polynesia around 30S 125W towards the end of the week, bit otherwise it looks like a week of trade winds in the Southwest Pacific, good for sailing west.


SUBTROPICAL RIDGE STR
There is still a leftover high in high latitudes, south of the low now crossing NZ — this high should travel northeast to 40S 140W by next weekend.

The STR generally seems to have finally shifted to its normal winter position of between 30 and 40S (it is about time, Tuesday is solstice). There are big gaps between its highs, one high is south of French Polynesia FP today and moving off to the east, enhancing easterly winds over FP. The next is making its way across central Australia and should shoot off a bud along 25S on Tuesday/Wednesday then move into central Tasman Sea along 40S next weekend, causing strong trade winds in the Coral Sea.

TASMAN SEA/NZ AREA
Last lot of cold air in the weekend trough is expected to wander east across North Island on Monday.
Then a weak ridge is expected to cross NZ on Tuesday/Wednesday.
Next 'Roaring 40s trough' should move across Tasman Sea on Tuesday and arrive over NZ from Wednesday night- waves of squally showers until a drying but cold southerly arrives next weekend (as high moves into Tasman Sea). This is likely to bring some useful snow at last to NZ ski fields.

SAILING TO/FROM NORTHERN NZ.
Best day to depart this week is Tuesday. And best day to arrive is Wednesday.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

12 June 2011

BOBGRAM7 issued 12 June 2011

WEATHERGRAM
YOTREPS
Issued 12 June 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.

NOTICE: Those of you who are on my weathergram list will notice a
change: as from next week I will be sending these from
bobmcd@xtra.co.nz, and so some of you (depending on your settings) may
find these weathergrams in your JUNK folder. If so, simple tell your
email program not to junk bobmcd@xtra.co.nz

Also please note that I helping manage MetService display at Fieldays
and will be unavailable to respond to email 14-18 June.

TROPICS
SOI is in neutral territory, in past week its 30day running mean rose a
little from 0.18 on 5 June to 0.73 on 12 June.

Monsoon has arrived in Mumbai; arrival time is a few days later than
normal this year and so far accumulated monsoon rain is 17% above the
Long Period Average. It has developed a double-barreled low, one to
west of India in Arabian Sea is now Cyclone ADRIAN and t'other, to east
of India, sort of fills the entire Bay of Bengal.

Galapagos to Marquesas: More of the same. Avoid the Equatorial current.
Dive south to around 5S 100W and then head almost due west to 7S 133W
and then head for landfall. No organised tropical showers around. But
if you are attempting the Panama to Galapagos leg, be aware that ITCZ is
strong to south of Panama.

South Pacific Convergence Zone was mainly located from Tokelau to
Australs along with an active clump about and east of Tonga/Niue.
It also has a squash zone on its southeastern side at present (Fiji Met
Service gale warning). It is now mainly around the Northern and
Southern Cooks, and may get to French Polynesia FP and may get to Samoa.


The convergence over PNG links across the Coral Sea with a mid-latitude
trough that is quasi-stationary in Northern Tasman Sea and trails
southeastwards well to east of NZ. A weak 'secondary' low is expected
to wander from west to east along this front/trough line mainly along
30S to 35S from Monday to Wednesday. Not enough to stop sailing between
NZ and Fiji/Tonga but needs to be taken into account.

SUBTROPICAL RIDGE
High in Australasian Bight is about to break free from its block and
should get onto Tasmania on Mon 13 June and cross Tasman Sea to reach NZ
on Thu/early Fri 16/17 June, and then expand along 40S to east of NZ,
enhancing the trade winds from FP to Tonga early next week.
Next high from Australia is likely to wander east across New South
Wales, indicating a possible end to the "low index" weather regime we
have been having for a while. Colder SW winds should then be able to
spread further north across NZ.

TASMAN SEA/NZ AREA
Some cold air is sideswiping Southland and Otago tonight and should
reach Chatham Islands on Wednesday and Thursday.

Another Low is likely to form off Queensland coast by Wed 15 June, and
this one should deepen a lot in mid Tasman Sea on Thursday and then move
SSE across Southland on Sat/Sun 18/19 June. Associated front should
cross NZ area on late Friday/early Sat, preceded by a northerly flow,
accompanied by rain and followed by a showery NW flow.

For Fieldays this year, prospects are for a dying SW on Wed/Thu, a foggy
ridge for Friday morning, then a band of rain starting Friday night,
easing Saturday afternoon, then showers.

For those returning to NZ after the NZ-Fiji yacht race, you can use the
N to NW winds of the Friday/Saturday front to some advantage, and, at
this stage, it looks a though Northern NZ should then have light winds
Sun 19 to Wed 22 June so that should ensure a good enough return voyage.


The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bobmcd@xtra.co.nz

05 June 2011

BOBGRAM7 issued 5 June 2011

WEATHERGRAM
YOTREPS
Issued 5 June 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.

TROPICS
SOI is in neutral territory and continues to hover just above zero. It
dropped to 0.3 on 22 may and has since continued falling, was 0.18 on 5
June.

No cyclones around at present.

Galapagos to Marquesas: More of the same. Avoid the Equatorial current.
Dive south to around 5S 100W and then head almost due west to 7S 133W
and then head for landfall. No organised tropical showers around.

South Pacific Convergence Zone SPCZ has weakened into clumps --- main
clump is around Tonga and Samoa (as a trough). This branch is likely to
stretch eastwards this week (the reason for this lies with the upper
winds). There is another weak zone in the North Coral Sea. This zone
should grow more extensive and spread southwards this week. And a
minor clump around Tuvalu to Tokelau. A zone of showers over French
Polynesia links with a mid-latitude trough.

SUBTROPICAL RIDGE
HIGH well above 1030 at 37S and south of Southern Cooks tonight has a
spread out squash zone of near gale easterly winds on its northern side.
This High has reached its peak and so has the squash zone. The high
should wander off to the east next few days, so that the fading squash
zone may visit the Australs on Tue to Thu 7 to 9 June.

Weak ridge starts to grow over NZ on Wed 8 June and this should expand
into a new High moving east along 40S to east of NZ over the rest of the
week.

SO, between Northland and Fiji - for the Auckland to Fiji race fleet -
there is a slack subtropical ridge over the next few days, and this
should firm into useful trade winds once this new high grows east of NZ.


NZ/TASMAN SEA
Weak trough crossing NZ on Tuesday followed by that growing high on
Wednesday (mentioned above).

The main feature in our region this week seems to start off as a Polar
outbreak affecting Tasmanian on Tue 7 June. This is expected to deepen
into an intense low off the New South Wales Coast on Wed 8 June and then
broaden across the Tasman on Thursday and finally cross central NZ when
it is decaying on Sat/Sun 11/12 June. If you have full Internet access,
then check this out at http://bit.ly/7daywx .

Australians need to be aware that 5 metre swells may form on western
side of this low on Tue/wed 7/8 June.

WHEN TO DEPART NZ?
With the predominantly northerly flow east of NZ over next few days, it
is as OK as it gets for departing east to Tahiti.

The light winds with the Wednesday ridge may make a good departure day
for power vessels going north, but not so good for sailing--- anyway the
incoming NW flow ahead of the Tasman Low closes this window from
Thursday 9 to Sat 11 June.

May be an OK day to sail north with the SW flow which is likely to
arrive after that Low, say on Sun 12 /Mon 13 June. BUT there may be a
deepening low in the North Tasman Sea early next week - and this may
reach NZ around Wed 15 May - that is the outlook from today's run of the
ECMWF model at http://bit.ly/ecoz .


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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