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

30 December 2012

BOBGRAM issued 30 Dec 2012

WEATHERGRAM

YOTREPS

Issued 30 Dec 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: Things are changing. The Southern Oscillation Index or SOI (30 day running mean) was hugging the plus 0.5 value since the beginning of September, but during December the 30-day average dropped to minus 1 by 23rd and is now -0.8. An interesting swing towards an El Nino.

As mentioned last time, TC FREDA did indeed form near Solomon Islands a few days ago and is indeed on its way to affect New Caledonia on Mon 31 Dec/Tue 01 Jan. The future track of FREDA is still unsure, but it MAY affect northern NZ on Sat/Sun 5/6 Jan. Stay updated if this is relevant to your excursions.


South Pacific Convergence Zone is active over the Cooks and has developed a tropical depression there. This low is expected to travel south and get knocked a little to the west by a HIGH that is moving away to the east along 45S. This track will take the Low closer to NZ by mid-week where it weakens and that may provide a trough line that will affect FREDA's future track.

There is also a TC off Western Australia called MITCHELL. It is travelling south and grazing the coast. It is expected to move a little to the west as it comes south, and weaken.

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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

23 December 2012

BOBGRAM issued 23 Dec 2012

WEATHERGRAM
YOTREPS
Issued 23 Dec 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 Ocean. Along the Pacific equator, Sea Surface temperatures SST have recently been near normal with some below-normal SST near Galapagos- this situation is considered to support ENSO neutral conditions and computer models are picking this to continue into 2013. There is a zone with SST around 1 or more above normal from Samoa to Tahiti and another off NW Australia—these can possibly encourage the formation of the South Pacific Convergence zone SPCZ during the next few months and bears close watching.

The Atmosphere: Things are changing. The Southern Oscillation Index or SOI (30 day running mean) was hugging the plus 0.5 value since the beginning of September, but during December the 30-day average has dropped to minus 1, and this is in response to lower than normal isobars over Tahiti, so it is a definite shift towards an El Nino-like episode. Interesting.
EVAN is out of the tropics and gradually unwinding like a wind-up Christmas kids toy. It has not been able to encounter a Jetstream or cold front from the southern ocean so is not going to re-intensify like SANDY did. It is going west-wards across northern NZ and is expected to be picked up there by upper NW wins and taken southeastwards across central NZ on Boxing Day. A good blog on the future track of EVAN can be found at http://blog.metservice.com/2012/12/christmas-weather-daily-update/

Next week?
At this stage GFS model is picking that another tropical low may deepen into a cyclone between Solomons and Vanuatu by Friday 28 Dec and then go SSE to cross New Caledonia area on Mon 31 Dec/Tue 01 Jan. EC model is not so certain as to the intensity of this system yet but agrees with the timing. If you intend to sail in this area then keep checking for updates, and maybe delay. The next name on the list for South Pacific Cyclone is FREDA.

Sydney/Hobart Race –The teams are getting ready for a great race – check out http://rolexsydneyhobart.com/ Weather forecast is for a dream start then NE winds then a westerly or SW change on Dec 28th. If the super maxi can get to Hobart before the westerly they may have a chance of beating the race record of one day, 18 hours, 40 minutes and 10 seconds, set by the then 98 foot super maxi, Wild Oats XI, in 2005.
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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

16 December 2012

BOBGRAM issued 16 Dec 2012

WEATHERGRAM

YOTREPS

Issued 16 Dec 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 Ocean Along the Pacific equator Sea Surface temperatures SST have recently been near normal with some below-normal SST near Galapagos- this situation is considered to support ENSO neutral conditions and computer models are picking this to continue into the new year. There is a zone with SST more than 1 above normal from Samoa to Tahiti—This can possibly encourage the formation of the South Pacific Convergence zone SPCZ during the next few months and bears close watching.

The Atmosphere: Things are starting to change. The Southern Oscillation Index or SOI (30 day running mean) has been hugging the plus 0.5 value since the beginning of September, but in recent days the 30-day average has dropped to minus 0.5, and this is in response to lower than normal isobars over Tahiti, so it is a definite shift towards an El Nino-like episode. Computer models are picking a neutral SOI for the cyclone season.

This edition of my weathergram is all about EVAN. TC EVAN started as a depression L that drifted east towards Samoa. It started intensifying faster than the computer models were expecting and dealt Apia a severe blow. Then it did a loop and went west and WSW. At present it is category 4 near the north end of Futuna and curving to the SW towards Yasawa. The latest forecast track map from Fiji Met Service shows past track, expected future track and possible variations (black line) and three rings at 12 hour time steps;
http://www.met.gov.fj/aifs_prods/65660.gif . The Fiji Met track map web page is very busy so if you need the latest track in a hurry try this URL to a gif image – it doesn't have the text of the full site so can only be used as an unofficial substitute. Remember to subtract 13 hours to convert the times shown here to UTC.

Note how small this system is, but it is extremely violent near centre during next 48 hours and then should ease to Cat 2 as it encounters cooler seas.

The low is expected to slowly continue south this week and become extra-topical. It is expected to bring cyclonic easterly winds and swell to northern NZ mainly around Sun /Mon 23/24 Dec.



http//bit.ly/7daywx gives the MetService model. The map for 1pm sun 23 Dec= 23 0000UTC issued this evening shows Low to north of northern NZ with just strong winds left, and these are spread out over a wide area.

Next week?

At this stage GFS model takes it across the North Island on Mon 24 Dec and EC model takes it west and weakens into a trough in the Tasman Sea (see http://bit.ly/ecoz). I think that by Boxing Day the winds may well be OK for Kiwi holiday sailing plans.]

Sydney/Hobart Race -Still too far away to be certain. In the map for next Sunday above you can see a heat trough deepening over the Aussie interior, and the possibility of a High forming over the Aussie Bight. One scenario is that this trough may break loose into the Tasman Sea on Boxing day and the High may then move towards the south of Tasmania—that would make a squash zone of enhanced S/SE winds mid-way between Sydney and Hobart in a word, challenging.

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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

09 December 2012

BOBGRAM issued 9 Dec

WEATHERGRAM
YOTREPS
Issued 9 Dec 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) had a value of MINUS 1.01 back on 25 Aug. It has been gradually rising ever since and on 02 Dec was plus 0.4, and by 9 Dec it has relaxed to plus 0.25. Computer models are picking a neutral SOI for the cyclone season.

Tropical cyclones: Last week TC BOPHA left behind a death toll of over 500 in the Philippines. It has changed course and is heading to Philippines again as a tropical storm.

South Pacific Convergence Zone SPCZ
If you are in the tropics then this is a week when the best thing to do is to stay put.

The South Pacific Convergence Zone SPCZ is dividing into three different zones of activity—one over northern Coral Sea, one between Fiji and Samoa and a third over the Southern cooks. There is now a zone of light north to NW winds on the northern side of the SPCZ, to North of 5S. So the SPCZ is turning into a trough of falling pressure.
The zone over Southern Cooks is expected to develop into a tropical Low on Monday or Tuesday that should travel westwards. There is already some cyclonic curvature showing in the cloud imagery.
The zone between Samoa and Fiji is expected to develop into a Low next-by around Wednesday or Thursday and may well deepen quickly into a tropical Cyclone that may be slow-moving over Fiji during the 15-16 Dec weekend. Avoid.

SUBTROPICAL RIDGE STR
The High over Northern Tasman Sea/North Island tonight is expected to weaken over the next few days. A new High is moving east across Tasmania on Monday, tugging the STR southwards as is expected during summer. This new high is expected to slide across central NZ on Thursday and then out to the east of the North Island next week. Its departure is likely to be a factor in the track of the tropical low over Fiji to the south.


NZ/Tasman Sea
Last Thursday's trough had a wedge of cooler air pushing into the warm pool on its eastern In the western flank of the warm pool there were some NW winds – these had started as part of that heat wave over Australia in the previous week. As these NW winds encountered the west coast of Auckland the friction difference between land and sea causes a convergence zone along the west coast line. As the extra upward motion of the wedge reached this convergence zone, it was able to fire a line of thunderstorms and one of these was severe enough to trigger a tornado. A rare event for west Auckland and this one led to three fatalities, put 7 in hospital and damaged around 200 houses.

This week's troughs are not expected to bring much--- one should fade over the South island on Monday and the next should linger over southern NZ from Friday 14 to Sunday 16 Dec.

There is likely to be a build-up of heat showers over the inland North Island on Wednesday and Thursday 12/13 Dec.

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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

02 December 2012

BOBGRAM issued 2 Dec 2012

WEATHERGRAM
YOTREPS
Issued 2 Dec 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) had a value of MINUS 1.01 back on 25 Aug. It has been gradually rising ever since and on 02 Dec was plus 0.4. Computer models are picking a neutral SOI for the cyclone season.

Tropical cyclones: Last week TC BOLDWIN was in the Indian Ocean. This week TC BOPHA is in the NW Pacific heading for the Philippines.

South Pacific Convergence Zone SPCZ
The South Pacific Convergence Zone SPCZ has stayed much the same in the past week between Solomons, Vanuatu and Fiji with a side branch from Tuvalu to Tokelau to Northern cooks. At this stage not such change is expected in the SPCZ during the coming week.

SUBTROPICAL RIDGE STR
The STR has been reasonably strong between 25 and 30S across the South Pacific during the past week and is expected to divide into High cells that may take a more southern route this week.
One cell stretched from 170E to 140W along 25 to 30S tonight and is expected to fade away by Tuesday, leaving behind a high near 35S to east of NZ. This high is expected to move east and intensify to a central pressure near 1020 near 150W by Saturday 8 Dec, with a squash zone of intensified trade winds over Southern Cooks.
Next high is expected to move off new South Wales into the central Tasman Sea on Thu/Fri/Sat 6/7/8 and then across central NZ on Sun/Mon to be mainly east of the South island at 40S by Tuesday 11 Dec. The following High may cross Tasmania on Tue/Wed 11/12 Dec—continuing this southern trend for the foreseeable future.


Between the migratory Highs there is room for a few troughs.
One is expected to move off the east of the North Island on Monday. Another is expected to deepen into a low as it crosses southern NZ on Tuesday and Wednesday. Without reprieve another Low is expected to deepen as it crosses NZ on Thursday and Friday- deepening to 980hPa as a large Low south of Chathams Islands. This Low is expected to support strong to gale SW winds and heavy SW swells in the Tasman Sea on Wednesday/Thursday. Avoid.
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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

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

28 October 2012

BOBGRAM 28 Oct 2012

WEATHERGRAM
YOTREPS
Issued 28 Oct 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 Ocean: Equatorial sea surface temperatures of our widest ocean act something like a thermostat for our weather engine—when they are sufficiently warmer than normal it is called an El Nino episode. Well they have been above average across much of the tropical Pacific over the last few months but are now relaxing.

Both NZ's NIWA and Australia's Bureau of Meteorology agree that the indicators are now pointing to less chance of an El Nino this summer than there has been recently. There is more chance that the coming cyclone season is likely to be in neutral territory, neither La Nina nor El Nino. This means that the weather patterns for the coming summer should be way-different from what was delivered by the La Nina we had last summer.

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 near zero for the past few weeks at around plus 0.2 to 0.3 during October. It's now in neutral mode.

Tropical cyclones have had a busy time in the Northern hemisphere in the past week. TC SON-TINH caused landslides claiming the lives of 25 in the Philippines. 15,000 people have been evacuated in the Philippines and 80,000 in south China. There is also a cyclone off the east coast of USA called SANDY, with a death toll of 58 when it was in the Caribbean.

As for our coming cyclone season. Here's a comment from NIWA: as given by Newstalk ZB: http://www.newstalkzb.co.nz/auckland/news/nbint/1621913505-pacific-cyclone-season-set-to-run-as-predicted
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Forecasting centres predict the number of tropical cyclones in the 2012 to 2013 season will be near or just above the average of 10.
NIWA says at least one category three or higher cyclone could occur anywhere across the Southwest Pacific during the season and all communities should remain vigilant.
New Zealand can expect at least one ex-tropical cyclone to pass within 550km of the country.
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South Pacific Convergence Zone SPCZ
The South Pacific Convergence Zone SPCZ has remained in scattered clumps in the past week and is mainly stretching from Solomons to east of northern Vanuatu, with another clump along 10S between Northern Cooks and Marquesas.
During the coming week the SPCZ should remain slow-moving, but its western branch may shift south and visit Fiji on Fri/Sat/Sun 2/3/4 Nov. Uncertain at this stage.

SUBTROPICAL RIDGE STR
One High is expected to move northeast across the Tasman Sea from Monday, fading away north of NZ on Thursday 1 November, with its remains following the normal STR path along 30S from Thursday to Sunday 4 Nov.
Next High is expected to take a more southern path, one typical of summer from Tasmania on Fri 2 Nov towards North Island by Sun 4 Nov--- but it may get blocked in the Tasman Sea. We shall see.


NZ/Tasman Sea
One Low is moving northeast-wards onto Northern NZ and should continue NE and then off to the east of the date line by Wed 31 Oct. There is a southerly to SW flow on its western side that may get as far as 20S between NZ and Fiji by Tuesday, with 3 metre swells as far as 25S. Not a major disruption but a cause of uncomfortable sailing.

The next trough should cross NZ on Thursday and Friday as a cold front followed by a SW flow.
After that there are two scenarios: the GFS is showing the High following this front to stretch along 40S to east of NZ , so that the SW flow gets converted into a SE flow stretching from NZ to Fiji/Tonga during next weekend of 3 and 4 Nov and early next week. ECMWF model, usually the more reliable, has the front stalling over northern NZ and forming a Low, and the High blocking in the Tasman Sea, so that the SE flow between these systems sits over NZ. SO if you are sailing this week, you'll need updates,

SAILING TO NORTHERN NZ.
There is a scarcity of wind for sailing from the Tropics to NZ this week, so it'll be slow. A sailing breeze is expected to return to the Niuas in Tonga by Thursday and to Tongatapu by around Fri/sat and to Minerva by Sat 3 November. If you want, you can use this time to motor south and get ready for breeze.

Rather than sailing into the SW/S winds on the back side of the low departing from NZ early this week (blue arrow in illustrated edition above), it may be better to try and capture the N/NW flow ahead of the next trough (jade arrow in illustrated edition above showing Wed position). The flow isn't expected to last long but it is the best on offer for sailing this week, and should be between New Caledonia and NZ on Thu 1 Nov, Fiji and NZ on Fri 2 Nov and Tonga and NZ on Fri/Sat 2/3 Nov.

The front that follows this N/NW flow may either stall near NZ until mid-next week (as seen in latest ECMWF model at http://bit.ly/ecoz, or be followed by SE then E winds (as seen in the GFS model that most GRIB viewers use). These are both OK patterns for sailing to NZ, with a few waypoints to avoid headwinds.

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If you sail via the Kermadecs there may still be some pumice rafts around.

The submarine volcano that produced these last July has recently been studied by NIWA.
Havre Volcano , NW of Curtis Island in the Kermadecs, had a massive eruption affecting the seafloor.
Illustrated edition shows NIWA's multibeam echo sounder image of Havre after its eruption in July. Crater is 5 kilometres wide and 800metres deep,

The pumice is no longer covering the entire sea, but rafts of it may still be encountered in quantities sufficient to block water filters. Some boulders are up to beach ball size. Illustrated edition some photos taken from Yacht Melina 4-12 Oct, within 500 nautical miles NW of Kermadecs (photos supplied with permission):

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See my yotpak at http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram illustrated edition is at http://metbob.wordpress.com/
Weathergram text only http://weathergram.blogspot.co.nz
Website http://www.metbob.com
Feedback to bob@metbob.com

21 October 2012

BOBGRAM issued 21 Oct 2012

WEATHERGRAM
YOTREPS
Issued 14 Oct 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 Ocean: Equatorial sea surface temperatures of our widest ocean act something like a thermostat for our weather engine—when they are sufficiently warmer than normal it is called an El Nino episode. Well they have been above average across much of the tropical Pacific over the last few months but are now relaxing. An El Nino may still occur over the next few months but it now doesn't look as though it will be a big one.
There seems to be a warming/cooling couplet occurring in the North Pacific.

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 near zero for the past few weeks at around plus 0.2 so far during 11 October. It's now in neutral mode, and may swing back into El Nino mode over the next few weeks.

In the NIWA rainfall outlook for the South Pacific for October to December a zone of drier than normal conditions stretches from Papua New Guinea to Tonga and for Southern Cooks (Fiji is greyed out meaning no clear indication). An above normal wet season is being forecast for places from Solomons to Northern Cooks and for Kiribati.

The South Pacific Convergence Zone SPCZ
This has weakening into scattered clumps in the past week and is mainly along 10S between Solomons and Northern Cooks and Marquesas.
During the coming week a trough is likely to stretch into the tropics from the mid-latitudes, crossing Fiji/Tonga on Thursday/Friday 25/26 Oct. This may help part of the SPCZ to shift southwards towards Vanuatu/Fiji around Sat 17 Oct and to New Caledonia on Sun 28 Oct. AVOID planning any departing voyages when the SPCZ is visiting. It brings troublesome tropical showers.

In the NIWA outlook for the SPCZ from October to December , the computed output (using dynamical models) – shows a slight shift to the north of normal near the Solomons and to the south of normal east of 180.

SUBTROPICAL RIDGE STR
One High is expected to move east along 30S to east of 180 from Monday marking the STR.
The next High in the STR should form in the mid Tasman Sea on Tuesday and then travel north into the North Tasman Sea by Thursday and Friday and then travel east along 30s crossing north of NZ on Fri/Sat 26/27 Oct. Using rhythm as a guide, the next HIGH to cross NZ should do so around Thu/Fri 1/2 Nov.


NZ/Tasman Sea
Between the highs in the STR there are lows and troughs.

One worrisome Low is being picked by the GFS model to deepen in the Tasman Sea near Norfolk island on Monday and then to wander eastwards along 30S, bringing an easterly gale to northern NZ on Tuesday night/Wednesday, and being followed by a vigorous SW/S flow reaching as far north as New Caledonia on Tuesday/Wednesday 23/24 Oct and Tonga on Thursday 25 Oct. The GFS model is the main one used for GRIB data so anyone watching these will see that a voyage to NZ from New Caledonia/Fiji/Tonga over the next few days will be uncomfortable.

Another very good model for checking weather patterns is the ECMWF as at http://bit.ly/ecoz, this has a slightly different scenario than the GFS, and the real pattern may lie between the two. Both models show uncomfortable voyages from the tropics to NZ this week so that I am compelled to advise everyone to simply take the week off and focus on enjoying the tropics.

Comfortable voyages to NZ MAY start opening up again on or after Thu 25 Oct. Too far away to be sure at this stage, so if you are ready to go then seek a weather update first. There may be another low crossing northern NZ around Sun/Mon 27/28 Oct something worth avoiding.

SAILING TO/FROM NORTHERN NZ.
If you are planning to sail from Tonga/Fiji/Vanuatu/ New Caledonia to NZ in October/ November, and looking to buddy with someone, then you may be interested in checking out the ICA's "All Points Rally" to Opua, see http://www.islandcruising.co.nz/. The group in Tonga are assembling for Big Mama's Birthday party late this week and will by then be able to tell if a departure around 29/30 Oct to NZ will be comfortable or not.
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See my yotpak at http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at http://metbob.wordpress.com/
Weathergram text only http://weathergram.blogspot.co.nz
Website http://www.metbob.com
Feedback to bob@metbob.com

14 October 2012

BOBGRAM issued 14 October 2012

WEATHERGRAM
YOTREPS
Issued 14 Oct 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 Ocean: Equatorial sea surface temperatures SST of out widest ocean act something like a thermostat for the weather engine—when they are sufficiently warmer than normal it is called an El Nino episode. Well they have been above average across much of the tropical Pacific over the last few months but are now relaxing. An El Nino may still occur over the next few months but it now doesn't look as though it will be a big one.
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index is a good site for latest on El Nino and SST.

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 near zero for the past few weeks and was plus 0.2 on 11 October. It's now in neutral mode, and may swing back into El Nino mode over the next few weeks.
These indicators show that, at this stage, the coming cyclone season may have an el nino touch to it but not much of a touch. NIWA are likely to add more info about this in the next few weeks.

Cyclones: Still busy in the northern Hemisphere with PRAPIROON and a tropical Low southeast of Japan, RAFAEL in the Caribbean and PAUL southwest of Mexico. Southern Indian Ocean has woken up with ANAIS heading for Reunion Island making an interesting early start for the southern Hemisphere cyclone season.

http://tropic.ssec.wisc.edu/# is a good site for latest on cyclones.

The South Pacific Convergence Zone SPCZ has shifted in the last week to the north of its normal range and stretches from Solomons to Tuvalu/ Tokelau/ Northern cooks and occasionally around Marquesas.
During the coming week it is likely to drift south, reaching Vanuatu to Fiji by the end of Tuesday and staying there until Friday. It is likely to arrive over the Tonga region the Tonga region around Friday 19Oct and linger there until it develops a Tropical Low that should then move off to the southeast early next week. AVOID planning any departing voyages when the SPCZ is visiting. It brings squally showers and these can be troublesome.

SUBTROPICAL RIDGE STR
STR is well defined at present. High that is crossing the Tasman Sea tonight is expected to move along the 25 to 30S latitude band by Thu 18 Oct. It has squash zone of enhanced wind both north and south of it. It followed by another using the 30 to 35 South latitude zone from Thursday 19 Oct to Sun 21 October. This high is expected to be gentler than its predecessor and only have a squash zone in the Coral zone.

NZ/Tasman Sea
The two Lows that crossed NZ on 8-9 Oct and 12-14 Oct deepened at the same time, bringing lots of wind and rain and consequent damage. This week we have a windy front crossing NZ on Thursday 18 and another on Monday 22 Oct- Note , that Monday is Labour day a public holiday in NZ commemorating NZ as the first [lace in the world to legislate the 8 hour working day (yeah, right). Next front over NZ is likely to be Thursday 25 Oct. These fronts are MOT expected to bring deepening Lows like last week, but it will be easier to arrive in NZ between them rather than during them.
Between the passing Highs, NZ continues to be subjected to a disturbed westerly flow, with LOWS forming and deepening in the mid-Tasman Seas on Monday and Tuesday 8-9 Oct and again on Friday to Sunday 12-14 Oct.
SAILING TO/FROM NORTHERN NZ.
We will soon be approaching the interesting part of the migration season which I call Analysis Paralysis of the Minerva Yacht Club. Cruising sailors are world renown for their ability to gather data from almost everywhere even in the remote Minerva, and then sharing their ideas with their neighbours in a great "show and tell" even if its just over the radio. The result is a committee of motion but no commitment to moving. The problem is that if you over examine the data something somewhere will always say "don't go".
So let me simplify things so you can work out when to go or no.
1: Avoid departing when the SPCZ is overhead or nearby.
2. Respect squash zones—they are not much of a problem this week except in the Coral Sea. Sometimes they can't be fully avoided.
3. Try to time your voyage (depending on the speed of your vessel) to AVOID arriving in NZ on the same day as a front. See dates given above.
4, - a corollary of 3… Fronts at this time of the year are usually less than a week apart and the voyage to NZ usually take more than a week, so front's can't be avoided altogether: better to arrange to encounter them near 30S in the STR where they are usually at their weakest. If things change then 30S is the place with deep water and open ocean, good for hoving to .
I hope these 4 tips help you decide.

And there's safety in numbers--If you are planning to sail from Tonga/Fiji/Vanuatu/ New Caledonia to NZ in October/ November, and looking to buddy with someone, then you may be interested in checking out the ICA's "All Points Rally" to Opua, see http://www.islandcruising.co.nz/ .

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

07 October 2012

BOBGRAM issued 7 Oct 2012

WEATHERGRAM
YOTREPS
Issued 7 Oct 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.

Just a brief weathergram this week…there will be more to write about next week.

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 near zero for the past week. It's now in neutral mode, and is likely to swing back into El Nino mode over the next few weeks.

The South Pacific Convergence Zone SPCZ remains active from the Coral Sea across northern Vanuatu and occasionally to Fiji, with another branch from Kiribati to Tuvalu to Tokelau across Northern Cooks towards Marquesas. The section that has recently been visiting Fiji and Tonga is expected to take a breather this week. The section over the northern Coral Sea may develop a tropical low near the Solomons on Monday and again next Saturday 13 Oct.

SUBTROPICAL RIDGE STR
High HI that briefly crossed the North Island today Sunday is expected to move steadily east along 25 to 35South getting to south of French Polynesia longitudes by Wed 10 Oct , producing a squash zone of enhanced trade winds on its northern side.

Next High H2 is expected to be over New South Wales on Monday and then weaken as it crosses the Tasman Sea and the North Island on wed 10 Oct and then spread east from NZ between 30 and 35S from Thu 11 Oct top Sun 14 Oct. By which time another High is likely to be over New South Wales. At present there seems to be a rhythm in these highs.


NZ/Tasman Sea
Between the passing Highs, NZ continues to be subjected to a disturbed westerly flow, with LOWS forming and deepening in the mid-Tasman Seas on Monday and Tuesday 8-9 Oct and again on Friday to Sunday 12-14 Oct.

SAILING TO/FROM NORTHERN NZ.
This next 'window" of OK conditions for approaching NZ from the north, at this stage, is Wed 10 to Fri 12 and again from Mon 15th to Thu 18 October.

If you are planning to sail from Tonga/Fiji/Vanuatu/ New Caledonia to NZ in October/ November, and looking to buddy with someone, then you may be interested in checking out the ICA's "All Points Rally" to Opua, see http://www.islandcruising.co.nz/ .

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And if you are heading for NZ from Tonga then you may like to know that vessels on this route have recently been reporting PUMICE near the Kermadecs. No one has reported any problems with this pumice so far.

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

30 September 2012

BOBGRAM issued 30 Sep 2012

WEATHERGRAM
YOTREPS
Issued 30 Sep 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 Ocean: The energy balance of our weather engine is thermostatically controlled by the sea surface temperature along the equator of our widest Ocean- The Pacific. For the past few months these have been between half and one degree ABOVE normal--- showing a tendency towards an El Nino period. Over the last few weeks the sun has been directly overhead the equator allowing this target area maximum solar input. Interesting the impact has been a small region of DECREASING anomalies. And in the sub-surface the region of positive anomalies has started to shrink—there is now a region of negative anomalies growing at depth in the mid Pacific. The impact of all this is that the probability of an El Nino episode dominating the weather engine is still high but now LOWERING, even though it remains above 50% for the remainder of 2012.
We are currently in neutral but volatile…by early 2013 neutral conditions (between El Nino and La Nina) are more than 50% likely.


The Atmosphere: The Southern Oscillation Index or SOI (30 day running mean) is stalling after a bounce back from its low of -1.01 back on 25 Aug. It east been hovering around plus 0.4 in the past week. So the atmosphere is locked into a monthly swing from El Nino to neutral. It's now in neutral mode, so is likely to swing back into El Nino mode over the next few weeks.

Tropical cyclones: Things are still ticking over with JELAWAT east of the Philippines last week and expected to make land fall over Japan in a few days. NADINE is looping around the mid-North Atlantic.

In the South Pacific, the South Pacific Convergence Zone SPCZ is now activating over the Coral Sea, drying out over Fiji and weakening east of the 180. During the coming week it is expected to weaken in the Coral Sea by Tuesday, stretch eastwards across Vanuatu on Wednesday and across Fiji and Tonga on Thursday and Friday. Avoid the active parts.

SUBTROPICAL RIDGE STR
High HI marking the STR in the east is currently near 43S way to the south of French Polynesia FP and is moving slowly east, cradling a large low that is moving slowly south along around 135W . This low is expected to deepen below 1000hPa on Monday, making for gales all around it and throwing some large swells to the south end of FP.

High H2 marking the STR in the west is taking a different latitudinal track from HI. It is currently in the Australian Bight and is expect to travel NE across eastern Australia on Monday Tuesday Wednesday and then east along 25S from Thursday to Saturday and then along 30S when it clears 180.

The next High H3 is expected to take a more southern latitude across Tasmania on Sat/Sun 6/7 October.

NZ/Tasman Sea
A disturbed southwesterly flow should cover NZ from Monday to Thursday. On Friday, as H2 zips like orange pit eastwards between Fiji and NZ, A strong NW flow should cover the Tasman Sea/NZ area, followed by a front and SW change on Saturday.
At this stage the most likely scenario is that this front may stall over northern NZ and allow a low to deepen there on Sunday and move off on Monday 8 Oct. This scenario may change by then so seek updates.
SAILING TO/FROM NORTHERN NZ.
This next 'window" of OK conditions for approaching NZ from the north, at this stage, is on Monday/Tue 8/9 October… if you are in a hurry to get here now then aim for those dates.

If you are planning to sail from Tonga/Fiji/Vanuatu/ New Caledonia to NZ in October/ November, and looking to buddy with someone, then you may be interested in checking out the ICA's "All Points Rally" to Opua, see http://www.islandcruising.co.nz/ .

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No bonus extras to this week's blog and next week's may be delayed a day or so.


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

23 September 2012

BOBGRAM issued 23 Sep 2012

WEATHERGRAM
YOTREPS
Issued 23 Sep 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 Ocean: Only small changes have occurred in the sea surface temperature anomalies in the equatorial mid Pacific during September so far. Generally things have stalled at around the plus 0.5C mark. So the recent trend towards El Nino is now on hold.

The Atmosphere: The Southern Oscillation Index or SOI is rebounding after August's dip. On 25 Aug its 30-day running mean was -1.01, and since then it has risen to plus 0.46 on 21 September. So the atmosphere keeps oscillating about and is not ready yet to dive into an El Nino episode. Even so, computer models are indicating that El Nina may slowly arrive by end of October.

Tropical cyclones: Things are still ticking over with JELAWAT east of the Philippines and MIRIAM off the west coast of Mexico.

In the South Pacific, the main branch of the South Pacific Convergence Zone SPCZ is now deactivating as it is stretched out across Solomons to Northern Vanuatu to Fiji to Tonga /Southern Cooks. There is another convergence zone from Tuvalu (weak) to Samoa to between Northern and Southern Cooks to the SE.

SUBTROPICAL RIDGE STR
High H1 east of NZ near Chathams tonight is expected to travel steadily eastwards mainly between 30 and 40S this week, and maintain a SQUASH ZONE of enhanced trade winds to its north at around 18 to 28S as it wanders eastwards.
High H2 is expected to move across the northern Tasman Sea from Tue 25 Sep. This is likely to divide into two. One part is likely to cross central NZ on Thursday and t'other is likely to go north of the North Island over the weekend.


NZ/Tasman Sea
A broad trough with several small features should slowly cross the country from Tuesday to Thursday, proceeded by a northeast flow on Monday and followed by a SE flow over the North Island on Friday. One of the features in this trough is likely to bring large WSW swells onto the South Island west coast on Wednesday 26 Sep. Otherwise, it is an OK week for sailing towards NZ.
SAILING TO/FROM NORTHERN NZ.
If you are planning to sail from Tonga/Fiji/Vanuatu/ New Caledonia to NZ in October/ November, and looking to buddy with someone, then you may be interested in checking out the ICA's "All Points Rally" to Opua, see http://www.islandcruising.co.nz/ .

THE EQUINOX
We had an equinox (Latin for equal night, but it is misnamed) yesterday 22 1449UTC. That's a special moment in the earth's orbit of our sun, and it fittingly picked by many to mark the start of the Southern hemisphere SPRING.
Many in NZ, for practical reasons, such as climatologists who measures averages, etc. on a monthly cycle, take the months of September, October and November to be Spring, but astronomers, for logical reasons, use the four 'corners' of the earth's orbit as markers (equinoxes and solstices).
The best definition of the equinox is when the sun, as seen from earth, is directly overhead the equator.

As viewed from earth the sun is directly overhead a different latitude every day of the year. The difference between this latitude and the equator is called the sun's declination, as all navigators know already.

On the day of the equinox some say it's a 12 hour day everywhere—that's true only if you measure sunrise and sunset using the mid-point of the sun. Sunrise and sunset tables actually use the top limb of the sun so that adds an extra 5 to 8 minutes of (rather dull) sunlight. The name given to the day with 12 hours exactly sunlight/darkness is the equilux - in Auckland that was 19 Sep (within 20 seconds).

From now on the days will lengthen. But the rate is not linear—Auckland's dawn is getting earlier at the rate of 10 minutes per week at present, but dusk is only getting later at the rate of 6 minutes per week. At the equinox the delimiter (line on the earth dividing day and night) is shaped like a square wave and during the next few months or so it slowly reshapes into a sine wave. You can watch this by downloading the program Home Planet from http://www.fourmilab.ch/homeplanet/ and watching this in the animate mode.

At this time of the year the days are getting longer at the rate of around an hour per month. It is thus a good time to do a switch to Daylight saving, and indeed in NZ we SPRING our clocks ahead an hour at 2am next Sunday 30 Sep. This rate starts easing from now onwards, but the extra sunlight is now affecting the weather patterns.
Our spin axis is NOT at a right angle to our motion around the sun: the 23 deg tilt influences our heating cycle. OK it nods the southern hemisphere closer to the sun than the northern hemisphere for the next six months – and we are now approaching the flatter side of our elliptical orbit for the next six months, but the MAIN FACTOR is to do with the concentration of sun beams over a smaller area (and, in the northern hemisphere, the spreading out over a wider area. A good explanation is given at http://www.youtube.com/watch?v=DuiQvPLWziQ.

There is a lag between the change in increasing sunlight and the spot with the warmest temperatures on earth. The lag in the ocean is a few weeks more than in the land. Currently the warmest SST band in the open part of the Pacific is at around 8 deg N.

Note that the 28C isotherm is the South Pacific already extends as far as between Samoa and Fiji, and is extending southwards at a steady rate. This is the time of the year that the subtropical ridge—that zone which divides the trade winds from the roaring 40s- starts to drift southwards. As it drifts south, the isobars on its southern side may bunch closer together in places, and that increases the disturbed westerly winds in the parts of the roaring 40s. This period, known as equinoctial gales, is likely to last until mid-November.
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See my yotpak at http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at http://metbob.wordpress.com/
Weathergram text only http://weathergram.blogspot.co
Website http://www.metbob.com
Feedback to bob@metbob.com

16 September 2012

BOBGRAM issued 16 Sep 2012

WEATHERGRAM
YOTREPS
Issued 16 Sep 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 Ocean: Only small changes have occurred in the sea surface temperature anomalies in the equatorial mid Pacific during September so far. Generally things have stalled at around the plus 0.5C mark. So the recent trend towards El Nino is now on hold.

The Atmosphere: The Southern Oscillation Index or SOI is rebounding after August's dip. On 25 Aug its 30-day running mean was -1.01, and since then it has risen to plus 0.39 on 16 September. So the atmosphere keeps oscillating about and is not ready yet to dive into an El Nino episode. Even so, computer models are indicating that El Nina may slowly arrive by end of October.

Tropical cyclones: Not as busy as last week but things are still ticking over with NADINE in mid Atlantis, LANE and KRISTY off the west coast of North America, and SANBA over southern Japan.

In the South Pacific, the Convergence Zone SPCZ is slowly reactivating after a quiet period. It is stretching from Solomons to the Rotuma /Wallis region to south of Samoa and then towards the southeast. It is not active all along this stretch but is likely to become more active this week. There is another convergence zone along 7 to 10S from 150 to 165W.
On Fri 21 Sep a convergence zone is likely to form over Fiji and this is ten expected to combine with an incoming trough from the west and produce a trough that crosses Fiji and NZ on Mon and Tue 24 and 25 Sep. Avoid.

SUBTROPICAL RIDGE STR
High H1 east of NZ near 33S 170W tonight is expected to travel steadily eastwards along 33 to 35S this week, and maintain a squash zone of enhanced trade winds to its north at around 15S as it wanders eastwards.
High H2 in Tasman Sea near 30S 160E tonight is expected to fade and stretch south and reform over and then to SE of NZ by Thursday 20 September. This weekend it is likely to travel NE and then, next week, it is likely to follow the track of H1.

NZ/Tasman Sea
This week is looking reasonable for travel between Northland and the Tropics and vice versa, with lightest winds over Northland on Wed 19 Sept. There is likely to be strong to gale NE and SW winds in places when the next trough crosses Northland on Mon and Tue 24 and 25 Sep. Avoid.

SAILING TO/FROM NORTHERN NZ.
If you are planning to sail from Tonga/Fiji/Vanuatu/ New Caledonia to NZ, October/ November, and looking to buddy with someone, then you may be interested in having a look at the ICA's "All Points Rally" to Opua, see http://www.islandcruising.co.nz/ for this voyage.

THE BEST TIME TO SAIL FOR NZ???
Well, some Insurance companies do not cover you vessel for any storm damage incurred in the tropics during cyclone season. Some companies say the SW Pacific cyclone season starts on 1 November and hence the early November rush. Other companies say the season starts 1 Dec. usually the first cyclone appears around mid to late December... but there have been very damaging cyclones such as BEBE as early as 10 Oct.
The Australian and South Pacific Cyclone RISK is still minor in the six weeks after the equinox (late Sept and during Oct) and 'acceptable' in October but rises rapidly in November and reaches the rate of around 1 per month by the end of December.
The strength of the disturbed westerlies near NZ is another factor in your timing calculation. These roaring 40s winds feed off the temperature difference between the tropics and the Polar regions. At the equinox (14:29 UTC next Sat 22 Sep.) the sun as viewed from earth is directly overhead the equator. This is when sunshine starts to return to the Antarctic Polar circle after 6 months of darkness. So Antarctica air temperatures are then the coldest of the year. So that temperature difference between tropics and pole is at the strongest of the year, So the roaring 40s are at their strongest and at their furthest north, covering NZ-- and they sort of hold this peak over NZ for the next six weeks.. These are called equinoctial gales, but I like to call them the gales of the Antarctic dawn.
Anyway the Roaring 40s generally start easing in November and have down so by December. So if you wish to time your voyage to NZ by this factor then you'll wait in the tropics for as long as you can.
The most popular time for yachts to take this spring migration is from mid-October to mid-November. It is a good idea to allow 2 or 3 weeks to the voyage and then watch the weather and depart the tropics so as to avoid the worst of the passing parade of troughs and fronts associated with the roaring 40s. These troughs and fronts are usually 5 to 7 days apart, and the journey usually takes around 9 days, so you have to go through at least one trough at some stage. Not a good idea to do so at the start or near the end of the trip, so that means usually deliberately arranging to go through one mid voyage, say at around 30S where these fronts usually are less intense that elsewhere. That's a good general strategy but it needs to be adapted according to the actual weather pattern at the time.
Cyclones tend to be triggered during an episode called of enhanced convection on the South Pacific Convergence Zone. These tend to come and go in a rhythm known as the Madden Julian Oscillation ... named after two meteorologists who identified it independently. The current state of the MJO can be seen at web sites such as http://cawcr.gov.au/staff/mwheeler/maproom/OLR_modes/h.6.MJO.S.html. This web site shows the intensity of convection of the convergence zones between 2.5S and 17.5S. Just remember that blue is bubbly (intense convection) and yellow is mellow (relatively clear skies). An MJO shows itself as a pulse of blue that travels from west to east. During the cyclone season they tend to occur once every 4 to 6 weeks. This is one of the parameters I watch as I prepare my weathergrams.
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It seems I made a typo a few weeks back with my mention of how to download and view the Fiji weather map via email, so here's the corrected version:
First: download and install PhysPlot from http://www.pangolin.co.nz/downloads/phys_su.exe
You can read more about this program at http://www.pangolin.co.nz/physplot. This program only works on computers using Windows operating systems.
Second: When you like you may download the Nadi Fleet code by sending an email to query@saildocs.com, no message header, with subject text "send nadi-fleetcode" (without the quote marks).
When the email arrives with the code, cut and paste it into a file called (for example). Fleet.txt on your desktop. Then use file>open in the PhysPlot program to open the fleet.txt program and the code is translated into a weather map.
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See my yotpak at http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at http://metbob.wordpress.com/
Weathergram text only http://weathergram.blogspot.co
Website http://www.metbob.com
Feedback to bob@metbob.com

09 September 2012

BOBGRAM issued 9 Sep 2012

WEATHERGRAM
YOTREPS
Issued 9 Sep 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 Ocean: No change since last week- Sea surface temperature anomalies in the equatorial mid Pacific have generally stalled at around the plus 0.5C mark. So the recent trend towards El Nino is now on hold.

The Atmosphere: The Southern Oscillation Index or SOI is relaxing after a dip during past month. On 25 Aug its 30-day running mean was -1.01, on 2 Sep it was -0.34, and on 9 Sep it was around zero. So the atmosphere remains neutral. At this stage the tropics are 'on hold'. Even so, computer models are indicating that El Nina may slowly arrive by end of October.

Tropical cyclones: It's still busy time in the North America with KIRK and LESLIE and MICHAEL and an area under Investigation west of Africa, but they are all staying well offshore, and doing a good job of venting off any extra energy in the atmosphere/ocean. In a way it's a pity the rain is remaining offshore. The northern American drought is now looking more intense as the African drought.
See http://www.eldoradocountyweather.com/climate/world-maps/world-drought-risk.html
This map shows that the Northern Hemisphere Sub tropical Ridge has been further north than normal over the past 6 months—this is related to the recent fading La Nina. The dryness of northern India is a result of weak monsoon rains there over last month or two—again this is associated with a fading La Nina episode.

In the South Pacific, the Convergence Zone SPCZ is starting to reactivate after a quiet period. It is likely to bring some heavy rain to Solomons tonight and Monday and to stretch eastwards along 10 to 15S reaching Tuvalu and Tokelau by early next week and towards northern Cooks by late next week 20-21 September.

This week we have the opportunity to see the transformation of a Convergence zone CZ into a trough.
A CZ is likely to form over Fiji and Tonga on Wednesday. This feature starts off as an extension of the SPCZ. A convergence zone is a feature that is marked by zone of converging surface air. This air piles upwards and then outwards creating a zone of enhanced convection. As air travels through a CZ it usually doesn't change direction much, and the CZ usually lingers around the same place.
During Thursday this CZ is likely to turn into a trough. That is to say that the air pressure lowers along its midriff, and there is a marked difference in wind direction across the convergence zone, with, in this case, NE surface winds on one side and SE winds on t'other. Also the whole system starts to move – in this case southeastwards due to the net NW winds at cloud level. A low is then expected to form late Thursday (UTC) near 25S 165W and deepen as it peels off to the SE , propelled by the upper winds and taking some of the moisture-energy of the CZ away with it to cause chaos in the Southern Ocean. The remains of the CZ are expected to turn into a trough that goes east and weakens, reaching French Polynesia by Sat 15 Sep.

If you are still in Tahiti and thinking about your voyage to Tonga in the next month or so, then watch this event closely and try and avoid a repetition of it during your voyage (Island hop between the troughs if you can).

SUBTROPICAL RIDGE STR
The STR lies between the trade winds and the roaring 40s. There have been some well formed highs travelling along the STR along 25 to 30S recently. One of these is now near south of FP and moving east.

The next is forming in the western Tasman Sea, but seems likely to form a centre near 42S on Tuesday. This High, combined with a low to southeast of NZ, should shovel some polar chilled air from near 60S onto the South Island . The High centre is expected to cross the North Island on Thursday 13 Sep and then move eastwards along 33S , followed by a Low that should form in the mid Tasman Sea on Friday 14 Sep.

NZ/Tasman Sea
The disturbed westerly winds of the roaring 40s are likely to bring a burst of SW swell into the Tasman Sea on Monday and Tuesday, and a low forming in the mid Tasman sea on Friday should cross the North Island on Saturday and Sunday. That really only leaves Wednesday and Thursday as good days for arriving/departing Northland.

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And now for some additional notes to what I wrote last week about obtaining weather maps via email. You may have invested in a some radio fax software such as Xaxero http://xaxero.com/downloads.htm or JVcom http://www.jvcomm.de/ or MScan http://www.mscan.com/ for downloading the sound from your shortwave radio and viewing it on your laptop, That's good. And there is also anap for your iPad called marine weatherfax viewer HD which might work – I can't vouch for it yet.

Winlink may allow you to download some radiofax maps via email as TIFF files from Noaa.
The list of instructions are at http://weather.noaa.gov/pub/fax/ftpmail.txt but there really are no maps that will help is the south pacific.

The Bureau of Meteorology Australia analysis maps for the South Pacific are
http://www.bom.gov.au/difacs/IDX0532.gif
and http://www.bom.gov.au/difacs/IDX0032.gif

And the Fiji analysis maps are at
http://www.met.gov.fj/aifs_prods/0992.jpg (3pm)
http://www.met.gov.fj/aifs_prods/0991.jpg (noon)
and http://www.met.gov.fj/aifs_prods/0990.jpg (6am)
Here's one for show :

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

02 September 2012

BOBGRAM issued 2 Sep 2012

WEATHERGRAM
YOTREPS
Issued 2 Sep 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 Ocean: Seas surface temperature anomalies in the equatorial mid Pacific have stalled recently or even relaxed a little and are all around the plus 0.5C mark. So the recent trend towards El Nino is now on hold.

The Atmosphere: The Southern Oscillation Index or SOI is relaxing after a dip during past month. On 25 Aug its 30-day running mean was -1.01, and on 2 Sep it was -0.34. So the atmosphere is in neutral, and that's different from last week's indicators.

Tropical cyclones: It's a busy time around North America with KIRK and LESLIE and an area under Investigation in the Atlantic, and ILENA + another rare under investigation in the Pacific. ISAAC made landfall near New Orleans around 7 years after KATRINA, but was a very low category hurricane and didn't pose much of a problem—rather, its rain has already been lapped up thank you.

The Indian Monsoon failed to deliver its normal dose of rain to some parts of India, but is now very wet over Myanmar/Burma, but dry over Indonesia/Malaysia, so it proving to be a mixed bag--- hard to use as an indicator.

In the South Pacific, the Convergence Zone SPCZ continues to be subdued. There is an active part over Papua New Guinea and Solomons. The zone of welcome rain that has been over Tuvalu/Kiribati /Tokelau is now weakening. Weak Convergence zones CZ are wandering from west to east across the South Pacific Islands, linking in with the transient troughs of the mid-latitudes further south. These systems move east because they are propelled by upper winds, but the surface winds around them are easterly.

This week there are two CZs in the pattern. CZ1 is moving away from French Polynesia FP tonight. CZ2 is bigger; it was over Vanuatu on Sunday and should cross Fiji on Tuesday, and Tonga on Wednesday. This CZ is expected to deepen into a LOW near 25S and to south of Niue on Thursday. Avoid this. The low should then go off to the SE and the CZ is likely to fade as it crosses the Cooks on Friday 7 Sep.

SUBTROPICAL RIDGE STR
The STR is in its normal position along 25 to 30S. The High cell near 170W is expected to wander eastward along 30S. This helps to squeeze the isobars on its northern side closer together, and thus accentuates the trade winds between Northern Cooks and Tahiti from Tue to Thursday 4 to 6 Sep.
Another high is expected to move into the north Tasman Sea on Tue and then wander east along 30S go that it gets east of the dateline by end of Friday 7 Sep UTC.

NZ/Tasman Sea
The strength of the polar vortex is measured by a parameter called SAM (Southern annular mode) and a proxy for this is the AAO (Antarctic Anomaly) at http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/new.aao_index_ensm.html . Its looking positive for the next few weeks, and that helps support the idea of disturbed westerly conditions for the Tasman Sea/NZ area.

One of these transient troughs in the disturbed westerlies is crossing NZ on Monday and the next is expected to do so on Saturday, followed by a day or so of vigorous SW winds with the Tasman Sea filling up with large but long-period southerly swells from the Southern Ocean

Traveling towards New Zealand this week:
Approaching NZ from the north between Tue 4 and Thursday 6 Sep is the go.
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Now is a good time for those of you in planning mode for sailing across the Pacific Ocean to check that you have access to good weather information. Sailmail offers good access to GRIB data, and to view these files you may use a grib viewer such as Viewfax at http:// www.siriuscyber.net/wxfax . Also you should download the Nadi Fleet code by sending an email to query@saildocs.com, no message, with text "send nadi-fleet", and view this in PhysPlot from http://www.pangolin.co.nz/physplot

Updates are also available from ZKLF Radio fax on 3247.4, 5807, 9459, 13550.5 or 16340.1 kHz Or High Seas on ZLM 6224 kHz and 12356 kHz at 0303Z, 0903Z, 1503Z and 2103Z and on 8297 kHz and 16531 kHz 30 minutes later or, for warnings, send email to query@saildocs.com, No subject, saying SEND http://m.metservice.com/warnings/marine
Or
SEND http://www.met.gov.fj/aifs_prods/10140.txt

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

25 August 2012

BOBGRAM issued 26 Aug 2012

WEATHERGRAM
YOTREPS
Issued 26 August 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 Ocean: Seas surface temperature anomalies in the equatorial mid Pacific have been increasing positive, and over much of the area they are now between 0.5 and 1C above. So it is trending towards an El Nino, but not there yet. Between Galapagos and South America a blob of cooler than normal water has welled up to the surface and is now slowly wandering westwards. Interesting.

The Atmosphere: The Southern Oscillation Index or SOI is steadying after a dip during past month. On 25 Aug its 30-day running mean was -1.01. So the atmosphere is now following the Ocean and trending El Nino, following the Ocean.

Tropical cyclones: ISAAC is at present attacking the tent city of 'quake refugees in Haiti and is likely to visit the Florida Keys later this week. In the NW Pacific we have TEMBIN still skirting around Taiwan, and BOLAVEN is heading to southwest end of Japan.

In the South Pacific, the Convergence Zone SPCZ continues to be fairly quiet. The part of the SPCZ over the Coral Sea seems to have shrunk to a zone over the Solomons. There is still a lot of convection between the Equator and 7S from 160E to 170W--- possibly due to the warmer than normal sea temperatures there. Another branch continues around Tokelau, and this seems to be lingering in place. A weak CZ is moving eastwards across the area around Niue and is likely to cross the Cooks on Monday UTC and fade over French Polynesia on Tuesday /Wednesday. In conjunction with this CZ a LOW is expected to form near 30S 155W/150W… this Low should quickly deepen and then move off to the ESE.
Anyone planning to go west from Tahiti this week should let that SPCZ pass by first.

A small CZ is expected to form over New Caledonia on Monday UTC. In conjunction with this CZ a low is expected to form near 30S 170-180E on Tuesday/Wednesday 28/29 Aug and this Low should then deepen a lot as it rolls off to the east southeast, expanding to dominate the weather in the Pacific next week to east of NZ.
These sub-tropical lows are able to feed off moisture from the SPCZ and energy in the nature of upper divergence from the subtropical Jetstream.

SUBTROPICAL RIDGE STR
The STR is mostly reverting to its Aug/Sep normal latitude of 30/35S this week. The High that crossed NZ late last week and is now just east of NZ is expected to slowly go north to 30S 165W by Wed 29 Aug and then should slowly make its way east. The High that is expected to cross the central Tasman Sea on Tuesday 28 Aug and the South island on Wed 29 Aug is likely to then be constrained to move east along 45S from Thurs 30 Aug to Sat 1 Sep.

NZ/Tasman Sea
A frontal system preceded by NW winds and followed by SW wind sis crossing NZ tonight/Monday. This system is at the intensity and latitude that is typical of spring, indicating that the Roaring 40s are now spreading onto NZ.
The next trough should start approaching NZ on Friday preceded by NW/N winds. This system is likely to form a low and then draw in a southerly change over NZ during Sat/Sun/Mon 1/2/3 Sep.

Traveling towards New Zealand this week:
In a simple roaring 40s scenario there is a rhythm in the weather with which you can arrange a reasonable sail to NZ. However this week there is a Low near 30S 170-180E on Wed/Thu 29/30 Aug and this poses a challenge. If you wish to approach NZ from the north this week, try and time your arrival day to be Sat 1 Sep.
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Now that we are at the end of August we can start forming ideas about the coming cyclone season. The SOI is hovering around -1, and such a low SOI is associated with an El Nino (we are not there yet but the trend is in place). During an El Nino the SPCZ tends to be shifted to north and east of its mean position , and this tends to encourage cyclones to form around or east of the dateline with fewer than normal near Australia.
A study of the number of Australian cyclones is available at http://www.aoml.noaa.gov/hrd/Landsea/oz/index.html. Using Figure 2 from this study and -1 for this year's value of the August SOI
we get an estimated count of 8 cyclones (for Australia) compared with the long term average of 11.

The Bureau advice at this stage on the cyclone season at http://www.bom.gov.au/wa/cyclone/seasonal/ is "The tropical cyclone season runs from 1 November to 30 April. The seasonal outlook for 2012/2013 will be issued on 15 October 2012."

I shall try and do some more research on this topic over the next few weeks?
See my yotpak at http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at http://metbob.wordpress.com/
Weathergram text only http://weathergram.blogspot.co
Website http://www.metbob.com
Feedback to bob@metbob.com

19 August 2012

BOBGRAM issued 19 Aug 2012

WEATHERGRAM
YOTREPS
Issued 19 August 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 Ocean: Seas surface temperature anomalies around the Galapagos are now relaxing back towards normal, but warmer-than-normal sea are shifting westwards into the central pacific, indicating we are on the verge of a new El Nino episode, but we are NOT there yet.

The Atmosphere: The Southern Oscillation Index or SOI is now dipping quickly. Its 30-day running mean rose during July from -1.21 to +0.27 and dropped to -0.65 by 12th August and -1.08 by 18 August. So the atmosphere is now tending towards El Nino, following the Ocean.

Tropical cyclones: In the NW Pacific we have TEMBIN heading for Taiwan, but it looks mediocre compared with HAIKUI a few weeks ago.
In the Atlantic we have GORDON with an eye near 35N and hurricane winds over Azores. This system is breaking a few of the rules but it is likely to fade after Tues 21 Aug west of Portugal.


In the South Pacific, the Convergence Zone SPCZ continues to be fairly quiet. There has been a weak CZ over the eastern Coral Sea occasionally affecting Vanuatu and New Caledonia. This looks to be reforming over Solomons this week.

Another convergence zone CZ has been lingering between 3 and 10South from 170E to 160W and then tapering off to the SE well east of French Polynesia FP- unusually north and east of normal for the SPCZ even for El Nino conditions. Some welcome rain for Kiribati. This is making another good week for sailing from Tahiti to Tonga without being bothered by the SPCZ. However the trade winds on route may be fresh to strong around 15S on Monday and Tuesday 20nd 21 Aug, and again around FP on wed/Thu 29/30 Aug. There seems to be a link between El Nino and strong trade winds.


SUBTROPICAL RIDGE STR
The STR is sticking to its northern latitude position along 20 to 30S cross much of the South Pacific.
Even the High centre near 45S 140W tonight is moving north-eastwards towards more tropical latitudes so that isobar patterns are approaching climatology in both western and eastern parts of the South Pacific.

A High is expected to move along 47S to south of Tasmania on Monday 20 Aug and cross the South Tasman on Tie 21 Aug and South Island on Wed 22 Aug and then move along 45S to 160W by Sat 25 August. The accompanying high marking the STR should move along 30S into N Tasman Sea on Mon20 Aug and then crawl towards North Island and fade there by Thursday 23 Aug.

Another High marking the STR should move along 30S into the North Tasman Sea on Sat/Sun 25/26 Aug.
NZ/Tasman Sea
South of the SR we have the roaring 40s plus some more in what has been a series of Tasman Lows all during August. There is one crossing central NZ tonight and going steady eastwards, but leaving a trough in its wake. Its upper trough should cross North Island on Monday evening. This should mark the end of the series: The next Low is likely to fade in the Tasman Sea on Sat and Sun 25 and 26 Aug.

Traveling towards New Zealand this week:
If you can time it, then aim to arrive in NZ on late Thursday, during Friday, or early Saturday (before next weekend's trough arrives).
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Anyone with internet access can see some of my talk as guest speaker last Monday to Cruising and Navigation Association of NZ'S Annual dinner:
1. Barcelona: http://www.youtube.com/watch?v=dErqR-AVzDc
2. America's Cup: http://www.youtube.com/watch?v=NL3lBpHJKdo
3. The winning formula: http://www.youtube.com/watch?v=rCwTj8bdRwk
4. El Nino/La Nina: http://www.youtube.com/watch?v=440FjhIQcyk&feature=plcp
5. Spring Outlook: http://www.youtube.com/watch?v=7gKlpxXflx4
6. Questions: http://www.youtube.com/watch?v=zv9WqsWYvCo

Also here is a link to a letter to NATURE magazine about how climate change is making the SPCZ more erratic:
http://www.csiro.au/en/Portals/Media/Warming-causes-more-extreme-shifts.aspx
Note that Raro Met man Arona Ngari is one of teh co-autours (well done-- pity the yachties can't get to rarotonga this year because of harbour reclaimation).

In the "Weathergram with graphics" this week is a satellite photo of the volcanic eruption around 85 miles SW of Curtis Island in the Kermadecs on July 17/18; this was the origin of teh rafts of pumice between Tonga and NZ during last few weeks. the volcano has since gone quiet.

There is also a photo of the WAKA that departed Auckland on Friday heading for Easter Island, as last leg of Hector Busby's mission (http://tvnz.co.nz/national-news/waka-crew-use-stars-easter-island-voyage-5029651)

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

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