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

25 November 2012

BOBGRAM issued 25 Nov 2012

WEATHERGRAM
YOTREPS
Issued 25 Nov 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 Atmosphere: The Southern Oscillation Index or SOI (30 day running mean) has a long time low of MINUS 1.01 back on 25 Aug. It has been gradually rising ever since and on 23 Nov was plus 0.5. Computer models are picking a neutral SOI for the cyclone season.


Tropical cyclones: The Indian ocean is now having the second cyclone of this season TC BOLDWIN. Another cyclone is likely to form near 5N 157E in the NW Pacific.

South Pacific Convergence Zone SPCZ
The South Pacific Convergence Zone SPCZ has gathered in strength during the past week between Solomons /Vanuatu and Fiji/Tonga. A tropical depression formed over Vanuatu and took a path southeastwards to south of Fiji and close to Minerva and then off to the south of Niue. This is similar to the Low we had a few weeks ago at the beginning of November, and we are likely to get such systems in the tropics around once a fortnight for the remainder of this cyclone season. If you are still in the tropics seeking to get out then try and do so between these systems. This coming week is looking like one of those weeks, between depressions.

SUBTROPICAL RIDGE STR
The STR is likely to stay along 25 to 30S this week as one high cell stalls and fades in the north Tasman Sea and another High forms behind the path taken as that Low which is tonight south of Niue moves off to the southeast . It sits as a dependable zone of fickle winds between the trade winds of the tropics and the disturbed westerlies of the roaring 40s.

NZ/Tasman Sea
A deep LOW below 970 hPa is moving east tonight along 60S across the South Tasman Sea and should peak and move NE on Wednesday when it is expected to be southeast of Chatham Island. Several waves of cold air are expected to be shovelled northwards onto NZ as this Low goes east and a High forms in the South Tasman Sea. Avoid getting between Low and High, for the SW swell may build to over 9 metres there. Each front should be colder and followed by wind more southerly than the previous, with one front crossing North Island) mainly eastern areas) on Tuesday, another on Thursday and the main one late on Friday. That last one is likely to open out into a significant trough and form a low east of the North Island, bringing a southerly change all the way to Tonga on Saturday. Worth avoiding.

If you are sailing to NZ this week from Tonga, the trade winds are looking OK for starters. Be prepared to motor through the light winds of the sub-tropical ridge. That Friday front may be useful for a sailing breeze at 25 to 30S even if it is followed by SW winds. From Saturday 1 Dec for a few days it will pay to head for a spot North and somewhat West of Opua , such as 33S 173E so that you are in position for sailing a few days of SW winds.
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See my yotpak at http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://metbob.wordpress.com/2012/11/04/weathergram-4/
Weathergram text only http://weathergram.blogspot.co.nz
Website http://www.metbob.com
Feedback to bob@metbob.com

18 November 2012

BOBGRAM issued 18 Nov 2012

WEATHERGRAM
YOTREPS
Issued 18 Nov 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.

This week's edition is shorter than usual while I attend a Met Society conference in Wellington.

The Atmosphere: The Southern Oscillation Index or SOI (30 day running mean) is relaxing after a bounce back from its low of MINUS 1.01 back on 25 Aug. It has been hovering around plus 0.2 to 0.3 since start of October, and was 0.35 on 18 November. Not much change. It's now in neutral mode. And forecast to stay that way for the rest of this cyclone season.

Tropical cyclones: There's a tropical depression in the Bay of Bengal, heading SW to Madras. Otherwise all is quiet.

South Pacific Convergence Zone SPCZ
The South Pacific Convergence Zone SPCZ has stayed in place from Solomons to the Tuvalu/Rotuma/Tokelau area, and is slowly intensifying. There are now some west to NW winds near the equator to north of Solomons and this is a danger sign that a tropical depression MAY form on the SPCZ during the next week--- most likely around Vanuatu or to east of there. Moving to south of Fiji by the end of the week. This bears watching and it may be a good idea to stay put if you are in the target area this week.

SUBTROPICAL RIDGE STR
The STR is likely to be shifted south this week down to the NZ area makes a zone a light and fickle wind that is hard for sailing but good for motoring.

See graphical edition of this blog for a Mid week weather map.

NZ/Tasman Sea
A low is expected to form over the Lord Howe Island area on Monday and then move east and merge into a trough over northern NZ.
With high pressures over central NZ and lower pressure to the north and south, it is likely to be a trough week for anyone approaching Northern NZ. The NE winds ahead of this trough may be OK for sailing south, but when they turn to be from SE, as on Friday-Sat-Sun 23-24-25 Nov, they may be blowing against you.
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See my yotpak at http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://metbob.wordpress.com
Weathergram text only http://weathergram.blogspot.co.nz
Website http://www.metbob.com
Feedback to bob@metbob.com

11 November 2012

BOBGRAM issued 11 Nov 2012

WEATHERGRAM
YOTREPS
Issued 11 Nov 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 Atmosphere: The Southern Oscillation Index or SOI (30 day running mean) is relaxing after a bounce back from its low of MINUS 1.01 back on 25 Aug. It has been hovering around plus 0.2 to 0.3 during October, and was 0.15 on 11 November. Not much change. It's now in neutral mode. And forecast to stay that way for the rest of this cyclone season.
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Tropical cyclones in the Northern Hemisphere are now quiet at last.
Bureau of Meteorology Australia have this to say about our cyclone season
(http://www.bom.gov.au/climate/ahead/south-pacific/tc.shtml)
Odds favour a near average tropical cyclone season for the South Pacific
• Near average tropical cyclone activity is the most likely scenario for the full South Pacific region.
• There is a tendency for average to below average cyclone activity in the western region of the South Pacific.
• Climate indicators which affect tropical cyclone activity show that:
o the tropical Pacific Ocean is currently neutral (neither El Nino nor La Nina);
o near-El Nino conditions have been present in 2012 and have been considered in this outlook.
________________________________________
The current, neutral state of the El Nino–Southern Oscillation (ENSO) would historically suggest the South Pacific region as a whole would experience near average tropical cyclone activity during the coming season. However, warmer than average sea surface temperatures in the central equatorial Pacific in July, August and September suggests slightly reduced odds of above average (slightly increased odds of below average) tropical cyclone activity in the western region of the South Pacific this season. Historically, the model has shown high skill in the west. This outlook is for the southern hemisphere tropical cyclone season which is usually considered to be between 1 November and 30 April.
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South Pacific Convergence Zone SPCZ
The South Pacific Convergence Zone SPCZ has slowly intensified during the past week and is mainly stretching from Solomons to Tuvalu to Tokelau to Southern Cooks. The tropical low that visited Tonga/Minerva last Wednesday (as mentioned in pervious weathergram) has taken a fair amount of moisture with it off to the southern Ocean. Part of the SPCZ is expected to move south onto Fiji on Tuesday and onto Tonga on Thursday or Friday this week.

SUBTROPICAL RIDGE STR
The STR should remain robust between 25 and 30S across the South Pacific this week. This makes a zone a light and fickle wind that is hard for sailing but good for motoring.
By the way, there's a solar eclipse around 13 2210UTC - See my previous Weathergram for more details.


NZ/Tasman Sea
Trough is crossing NZ on Monday/Tuesday 12/13th and moving away on Wednesday 14th. Another is visiting on Thursday 15th, and another on Sat/Sun 17th/18th with disturbed westerly flows in-between. This week these troughs are expected to have little impact to north of 30 South.

SAILING TO NORTHERN NZ.

This week is the opposite of last week. We have occasionally unsettled weather at the NZ end of the voyage and mostly OK weather in the tropics and the STR. Try and time your voyage to arrive in Northland between fronts.

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NEIEIDA RTW
I am supporting Jeanne Socrates (69) in her quest to complete a solo unassisted circumnavigation sailing (RTW) on her yacht NEREIDA. At this end I am watching her weather as she sails around the world.

Jeanne took off from Vancouver, Canada last month and is now entering into the trades winds west of California.

You can read about her adventures from her web site at http://www.svnereida.com and this links to her fundraising page at http://www.justgiving.com/jeannesocrates.

If one of your loved ones has been taken by cancer and you like watching RTW sailing then I recommend you contribute to this site as a memorial.


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See my yotpak at http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://metbob.wordpress.com/2012/11/04/weathergram-4/
Weathergram text only http://weathergram.blogspot.co.nz
Website http://www.metbob.com
Feedback to bob@metbob.com

04 November 2012

BOBGRAM issued 4 Nov 2012

WEATHERGRAM
YOTREPS
Issued 4 Nov 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 Atmosphere: The Southern Oscillation Index or SOI (30 day running mean) is relaxing after a bounce back from its low of -1.01 back on 25 Aug. It has been hovering around plus 0.2 to 0.3 during October, and was 0.4 on 4 November. It's now in neutral mode.

Tropical cyclones in the Northern Hemisphere have quietened down since SON-TINH and SANDY. There is a tropical depression between Mexico and Hawaii called ROSA but it is just likely to go west and fade.

South Pacific Convergence Zone SPCZ
The South Pacific Convergence Zone SPCZ has slowly intensified during the past week and is mainly stretching from Solomons to northern Vanuatu to north of Fiji, with another clump along 10S between Northern Cooks and Marquesas.
Late Tuesday a tropical low is likely to form near Fiji and then deepen rapidly and move southeast across southern Tonga/Minerva possibly with gales and then go off the SSE. Avoid. It might earn itself a name as cyclone number 1 for the South Pacific season 2012/13.

SUBTROPICAL RIDGE STR
The new high crossing the Tasman One today should be held in place aloft and take all week to cross New Zealand. This offers a good opportunity to anyone wanting to sail to NZ - but those sailing from Tonga should already have left in order to escape the Wednesday Low.

NZ/Tasman Sea
Low is expected to form off Sydney on Friday 9 November and its trough should cross NZ on Monday/Tuesday 12/13 Nov.

SAILING TO NORTHERN NZ.
This week is probably the busiest of the year foe NZ arrivals, and we are having a high, so that's good.

The hard weather is at your departure zone. If you are in Tonga you'll now need to wait for that Wednesday low to blow through and the swells to settle again, maybe 10 November, so not this week. If you are in Brisbane the easterly winds are against you. If you are in New Caledonia then time your departure to make best use of the SW winds following the low crossing NZ on 12/13 November. If you are in Fiji there are many options.

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One thing that sailors heading for New Zealand over the next week or two may want to consider is the total solar eclipse on the new moon on 14 November. Its track is roughly WNW to ESE on a line north of NZ. Timing your voyage to catch is will be complicated, but imagine the kudos.
For more info http://eclipse.gsfc.nasa.gov/OH/OH2012.html#SE2012Nov13T

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See my yotpak at http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://metbob.wordpress.com/2012/11/04/weathergram-4/
Weathergram text only http://weathergram.blogspot.co.nz
Website http://www.metbob.com
Feedback to bob@metbob.com

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