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

27 May 2012

BOBGRAM issued 27 May 2012

WEATHERGRAM
YOTREPS
Issued 27 May 2012
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.

The Southern Oscillation Index or SOI has relaxed to near zero. Its 30 day running mean started May at -1.1 but went to plus 0.5 in mid-May and was -0,14 on 27 May.

Indian Monsoon was running slightly ahead of the normal schedule but is now on its normal schedule.

In the South Pacific, the Convergence Zone SPCZ is now active between 4 and 10S from 133E all the way to 173W. It then spirals into a new low deepening near 18S 165W or between Niue and Southern Cooks. This Low should continue to deepen as it moves south-south-eastwards into the mid- latitudes. The SPCZ that is left behind in this process is expected to stay in much the same place this week. Another Low may form on the SPCZ in the Coral Sea around Sunday 3 June and move SSE into the Tasman Sea early next week. This should provide an interesting challenge to this year's Auckland to New Caledonia Yacht race starting this Queen's Birthday Weekend (NZ Holiday).

Galapagos to Marquesas: A continuation of last week and all clear of squally showers. Depart quickly SSW from Galapagos until 3S then WSW to 5S then west to 125W then direct.

SUBTROPICAL RIDGE STR
High that is south of French Polynesia at 40S should wander slowly east.
High in the Australian Bight should cross the Tasmanian area on Thursday and South Island on Sat 2 June, then Northern NZ on Sunday 3 June and then peel off to the NE of NZ on Monday 4 June.
Between these Highs the STR is very weak and Lows are allowed to play.

NZ /Tasman Sea troughs
A trough is moving across NZ tonight and should stall long enough to east of North Island to allow a Low to form there on Monday. This Low is expected to dance and play in the area NE of North Island on Monday to Wednesday and then move off to the east on Thursday and Friday. A front from the Southern Ocean is expected to cross the South Island on Thursday and bring a dose of southerlies and heavy swell to eastern North Island.

Departing from NZ for the tropics:
Wind flow over northern NZ for most of the week is likely to be from the south and southeast, but it may be strong at times with large swells because of the Low. This can be considered to be spirited by some and uncomfortable by others. These conditions are expected to weaken by the time the Auckland to New Caledonian Yacht race commences.

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

20 May 2012

BOBGRAM issued 20 May 2012

WEATHERGRAM
YOTREPS
Issued 20 May 2012
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.

The Southern Oscillation Index or SOI has bounced back into positive territory over the past few weeks. Its 30 day running mean started May at -1.1 but was plus 0.5 on 13 May and plus 0.2 on 20 May. It is erratic.

Indian Monsoon is one week ahead of its normal position. The Everest–climbing window seems to be around May 25th and could last shorter than normal this year. See http://explorersweb.com/everest_k2/news.php?id=20845

In the South Pacific, the Convergence Zone SPCZ has slowly activated its intensity across the Coral Sea and northern Vanuatu then splitting into two zones – one over northern Fiji and central Tonga, and another to south of Fiji and over Minerva. This southern zone is now easing and the northern zone is expected to move northwards to Samoa this week.

Next weekend around 26/27 May a low could form on the SPCZ over Southern Cooks and then move off to the south. This is something to go clockwise around for vessels on the NZ to French Polynesian route.

Galapagos to Marquesas: A continuation of last week, all clear of squally showers now. Depart quickly SSW from Galapagos until 3S then WSW to 5S then west to 125W then direct.

SUBTROPICAL RIDGE STR
The STR is weak, and has allowed a large Southern ocean Low to extend as far north as 30S to east of NZ during the past week. The cold air arriving over NZ has brought about the Kiwi version of the 'Californian flush' – a name given to the arrival of winter in California which triggers yachties to head for the tropics. The weather pattern still looks good for those who left late in the week for their trip to the north.

Next subtropical high is over New South Wales tonight and should slowly go east across Northern NZ on Tues to Fri 22/25 this week with disturbed westerly flow over the South Island.

NZ /Tasman Sea troughs
A LOW should deepen rapidly off Sydney on Fri/Sat 25/26 May and cross the Tasman Sea and then central NZ mid-next-week. Avoid.

Departing from NZ for the tropics:
On Monday a small trough, left over from last week's cold air, is expected over Northland with showers.
Then Tue/Wed 22/23 May are likely to have light winds in a passing ridge. Then Thu/Fri/Sat 24/25/26 May should see one of those fronts crossing the South Island get north to Northland. Then early next week will be upset by northerly wind and the fronts associated with the approaching low.

So there are no good departure days from Northland to the tropics this week.

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

13 May 2012

BOBGRAM issued 13 May 2012

WEATHERGRAM
YOTREPS
Issued 13 May 2012
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.

The Southern Oscillation Index or SOI has bounced back into positive territory over the past week. Its 30 day running mean was mainly -0.6 in April, and started May at -1.1 but is plus 0.5 on 13 May. It is erratic.

Indian Monsoon seems to be arriving a few weeks ahead of schedule. See http://apdrc.soest.hawaii.edu/projects/monsoon/realtime-monidx.html .
It is too windy at present for those seeking the Himalayan Climbing window.

South Pacific Convergence Zone SPCZ has become quieter during last week, but is reasonably active across the Coral Sea, northern Vanuatu and Rotuma. It isn't expected to do much during the coming week.

Galapagos to Marquesas: A continuation of last week, all clear of squally showers now. Depart quickly SSW from Galapagos until 3S then WSW to 5S then west to 125W then direct.

SUBTROPICAL RIDGE STR
The STR is weakening around the date line as a large LOW from the southern Ocean expands its circulation northwards to around 25S. The old HIGH eats of NZ should move slowly east along 30S.

A new HIGH from the Aussie Bight is expected to cross New South Wales on Wed /Thu 17/18 May and move into the Tasman Sea on Friday 18 May. It will likely track along 30S, to north of NZ, by Mon 21 May.

NZ /Tasman Sea troughs
A LOW moved out and northeast-wards past Tasmania and into the Tasman Sea during this weekend. It is still expanding northwards and its associated front and disturbed westerly gales are likely to reach as far north as 30S. The SW winds on its western side are likely to draw air from 55S to NZ on Tuesday and Wednesday and then the Low may bottom out below 970hPa on Friday near 50S 160W—try and avoid this beast.

Departing from NZ for the tropics.
The SW flow over Northland should start easing on Wed 16 May; at this stage, things are looking good for those departing Thursday 17

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

06 May 2012

BOBGRAM issued 6 May 2012

WEATHERGRAM
YOTREPS
Issued 6 May 2012
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.

The Southern Oscillation Index or SOI is now diving more into negative/ nearly El Nino territory. Its 30 day running mean was mainly -0.6 in April, and had a dive to -0.8 around mid-April. It has started May with a dive to -1.1 on 6 May. If it can maintain this for three months 9and that's a big IF at this stage) then we' can call it an El Nino with weak trade winds and lots of SW winds over the Tasman during winter.

South Pacific Convergence Zone SPCZ had an interesting week with a build in activity across the northern Coral Sea, and between equator and 5South from 170E to 170W. Another branch has been active across French Polynesia and Pitcairn and to the southeast

SPCZ is likely to drift south across Fiji on Tue/Wed and Tonga /Minerva on Thursday 10 may in response to a passing mid-latitude trough. Then it should revert to a northern position.

Galapagos to Marquesas: All clear of squally showers now. Depart quickly SSW from Galapagos until 3S then WSW to 5S then west to 125W then direct.

SUBTROPICAL RIDGE STR
A northerly drift of the STR is noticeable, as is typical of this time of the year.
The High departing from NZ is starting off at 42S and then trending NE to near 32S when south of Rarotonga by Thurs 10 May.
The Next High of the STR is in two latitude bands. The one that is near 30S struggles to make impact. It is over inland New South Wales at present and gets to cross Tasman on Fri/Sat 11/12 May then fades. Its companion now near 55S to SW of Tasmania is expected to start going NE when it gets past Campbell island on Thursday 10 may and then expand to NE of NZ.
NZ /Tasman Sea troughs
Mid-latitude trough currently in mid-Tasman Sea has several features doing their own things. The LOW east of Tasmania should go SSE into southern ocean. The feature east of Lord Howe should turn into a LOW and cross central NZ on Tue and Wed 8/9 May then go off to the east—so there will be a squash zone between it the southern high.
Another southern Ocean LOW is expected to affect Tasmania on Friday 11 May and its cold NW then westerlies should spread onto NZ Sun to Wed 13 to 16 May followed by a southerly Thu 17 May .
NZ to Tropics
It's safe to say that this trough moves off North Island in dribs and dabs on Wednesday and that Thursday/Friday are looking to be OK days to depart Northland. This window 'closes; on Saturday 12 May IF something does form in coral Sea on Wed 16 may as predicted by GFS … but the EC model has a wider window, with no Coral Sea development .. see http://bit.ly/ecoz – we should be able to say more in this later this week.
The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback: bobmcd@xtra.co.nz, or bobmcdavitt@hotmail.com

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