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

25 August 2013

BOBGRAM issued 25 Aug 2013

WEATHERGRAM

YOTREPS

Issued 25 Aug 2013

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.

Background influences
The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin.
It maintained a value over 1 for most of June, hinting at a La Nina. Since then it has relaxed to around 0.1 (25 Aug).

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet.
This parameter has been near average so far this year, slightly on the cool side.

GLOBAL TROPICAL TOPICS

The flooding in Manila last week has been caused by a double whammy of monsoon rain and a tropical storm (TRAMI) dumping more than an average month of rain in a day. Rain in the area returned to normal last week. TC PEWA is also making its way to the NW in the NW Pacific. TC IVO is fading off the Baja Californian coast—unlikely to interfere with the final race of the Louis Vuitton in San Francisco.
Trade winds have weakened in the South Pacific between Australia and the dateline recently and the South Pacific Convergence Zone SPCZ has been stronger than normal between Papua New Guinea and Fiji/Tonga.

WEATHER ZONES

South Pacific Convergence Zone SPCZ
The SPCZ currently extends from Solomons to Fiji/Tonga and is increasing in intensity. It is expected to stay in much the same position during this week, but SE trade winds over Vanuatu and Coral Sea are expected to become strong in a squash zone as a slow-moving High forms in the Tasman Sea. There is a smaller Convergence Zone CZ along 10S around Northern cooks.

Sub-tropical Ridge STR
The new High moving into the Tasman Sea is a slow-moving one – the first we have had in several weeks, and this provides a good pattern for sailing between NZ and the Tropics.

Roaring 40s and New Zealand
Low that crossed northern NZ on Sunday is expected to move off quickly on Monday. Next trough is expected to arrive over South Island from southern ocean on Wednesday and over North Island on Thursday and then deepen into a low east of the North Island on Friday and doesn't move off to the east until Sunday. This is a classic setup for an "old man southerly" in Wellington that lasts three days. And it introduces another week if winter to NZ after a mild few weeks.

Route Briefings
Tahiti to Tonga:
As was the case last week, this week's weather pattern is looking Ok for sailing from Tahiti to Tonga or Samoa via the northern route (passing Suwarrow/Suvorov). There are not many troughs or convergence zones to worry about; however it is not expected to be entirely squall-free.
The southern route --- going via Southern Cooks /Niue—is second best this week because there is a trough that is expected to visit Southern Cooks on Tuesday/Wednesday (Monday/Tuesday local)

Between NZ and Fiji/Tonga
The slow-moving high entering the Tasman Sea offers a good pattern for travelling north with departures on Monday and Tuesday. After that the voyage is likely to be affected by that trough crossing the North Island on Thursday.

See my yotpak at http://lnk.ie/I9PE/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/I9PF/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/I9PG/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/I9PH/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

18 August 2013

BOBGRAM issued 18 Aug 2013

WEATHERGRAM
YOTREPS
Issued 18 Aug 2013
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.

Background influences.
The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin.
It maintained a value over 1 for most of June, hinting at a La Nina. Since then it has relaxed to around 0.5 (18 Aug).

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet. This parameter has been near average so far this year, slightly on the cool side.

GLOBAL TROPICAL TOPICS
Tropical Depression ERIN is weakening in the North Atlantic and it becomes subtropical. TC TRAMI is expected to take a path westwards into China to north of Taiwan this week, after TC UTOR killed at least four people and displaced more than 320,000 in Southern China las6t week. TC PEWA is also making its way to the NW in the NW Pacific. The Cyclone season is getting busy.
Monsoon seems to be weakening. In fact rain around the planet seems to have been below par last week, with the wettest zone in the South Pacific being from Samoa to Suwarrow.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ currently extends from Solomons to Tuvalu/Samoa to west of Tahiti at present and is expected to divide into two branches during the week, with one near 10S and the other between Fiji and southern Cooks. A small but intense and squally LOW may form on the SPCZ and visit northern Vanuatu on Wednesday and then move SE. Avoid.

Sub-tropical Ridge STR
There is part of the STR between NZ and Fiji/New Caledonia with a weak extension further east. There is a strong and slow-moving High over Australia and this is expected to finally start moving east into the Tasman Sera after Sat 24 Aug-not before.
The High that is east of NZ by mid-week is expected to move northeast from out of the southern ocean, and so is a cold high. There should be a squash zone of strong winds on its northern side. The SAM (Southern Annular Mode) index became very negative last week, indicating that any southerly outbreak – such as that on the eastern side of this high- is polar-chilled.
A low crossed northern NZ on Saturday and is expected to continue to move east along 35 to 30S this week, between the two ridges.

Roaring 40s and New Zealand
A disturbed and sometimes showery northerly/westerly flow is expected over NZ this week.

Route Briefings
Tahiti to Tonga:
This week's weather pattern is looking Ok for sailing from Tahiti to Tonga or Samoa via the northern route (passing Suwarrow/Suvorov). There are not many troughs or convergence zones to worry about; however it is not expected to be entirely squall-free.
The southern route --- going via Southern Cooks /Niue—is second best this week because there are several troughs expected to make their way eastwards between 18 and 25S associated with the low that is expected to travel east along 35 to 30S.

Between NZ and Fiji/Tonga
The disturbed northerly/westerly flow this week is not a good weather pattern for going north or south. If a slow-moving high does enter the Tasman Sea this weekend then there may be an OK pattern for sailing north starting early next week.

See my yotpak at http://lnk.ie/I4K6/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/I4K7/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/I4K8/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/I4K9/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

11 August 2013

BOBGRAM issued 11 August 2013

WEATHERGRAM
YOTREPS
Issued 11 Aug 2013

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.

Background influences
The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin.
It maintained a value over 1 for most of June, hinting at a La Nina. Since then it has relaxed to around 0.7.

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet.
This parameter has been near average so far this year, slightly on the cool side.

GLOBAL TROPICAL TOPICS
The Atlantic hurricane season is on track to be above normal from mid Aug to late October.
http://lnk.ie/HYEL/e=bobmcd1.bobgram@blogger.com/http://www.noaanews.noaa.gov/stories2013/20130808_atlantichurricaneupdate.html

At present there are two TC's. One, called UTOR, is tracking across northern part of Philippines and is expected to make landfalls to SW of Hog Kong on Wednesday. T'other, called Henriette, is traveling from east to west along path south of Hawaii. The winds of the SW Monsoon over India are starting to ease, compared with last week.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is expected to spend the first half of this week along roughly 10 to 12S. After Wednesday 14th UTC it is expected to drift southwards across Samoa, then it should cross Suwarrow on Friday and Southern Cooks on Saturday forming a Low near 23S 160W by Mon 19th UTC that is then expected to deepen and move off to the SE. This is likely to be a squally trough, one to avoid if possible.

Sub-tropical Ridge STR
The STR starts the week off strongly at its winter latitude of round 25/30S.
The High cell over central Australia on Wednesday is expected to cross the northern Tasman Sea on Friday and then the North Island on Saturday and move off to the east from Sunday.

Roaring 40s and New Zealand
A disturbed and boisterous westerly flow covers the mid-Tasman Sea and North island until Wednesday, albeit with the brief calm of a passing ridge on late Monday UTC. Thursday may be an OK day for departing to the north, but the NW/SW winds of the next trough are then likely to be encountered by Tuesday/Wednesday 20/21 Aug.

Route Briefings
Tahiti to Tonga:
Avoid that trough that is expected to cross Samoa on Wed/Thursday UTC and Suwarrow on Friday, Southern cooks from Saturday 17th UTC. If you depart early in the week you should be able to reach Suwarrow or Palmerston before the trough does, and wait out the passing trough there.
I am unsure how to compare the sheltering conditions of Suwarrow and Palmerston… I think Suwarrow will have a briefer impact than Palmerston from this trough, so maybe if you do intend to start this voyage this week, then leave early and go to Suwarrow and no further.

Between NZ and Fiji/Tonga
Travelling south arrange to arrive between Sat 17 and Tue 20 Aug.
Going north, there may be an OK departure on Thursday/Friday 15/16 Aug, but after that these voyages are likely to encounter Northerly winds by Tuesday 27th.

See my yotpak at http://lnk.ie/HYEM/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram text only and translator is http://lnk.ie/HYEN/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Weathergram with graphics is http://lnk.ie/HYEO/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Website http://lnk.ie/HYEP/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

04 August 2013

Bobgram issued 4 Aug 2013

WEATHERGRAM
YOTREPS
Issued 04 Aug 2013
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.

Background influences
The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) sums up the weather pattern over the South Pacific as one number. It is based on the standardised difference in the barometer readings between Tahiti and Darwin. It maintained a value over 1 for most of June, hinting at a La Nina. During early July it dropped to around 0.7 from kid to late July and rose to 0.9 in early August.

The Ocean: The warmer the sea the quicker it evaporates, tossing water vapour into the air, where is rises and cools into cloud. The equatorial Pacific region hosts the warmest sea on the planet. Thus its sea surface temperatures SST may be thought of as a factor in the running of planetary weather engine. An index for this is NINO3.4 and its abnormalities tend to influence changes in clouds along the equator and thus tweak the latitude zones of weather around the planet.
So far this year NINO3.4 has been on the cool side, but rather weak.

GLOBAL TROPICAL TOPICS
There has been some unusual tropical action over Hawaii, FLOSSIE made landfall, and now GIL is weakening as it takes a track south of the Islands followed by another tropical depression.
Over Asia, SW/W Monsoon wind and rain have relaxed a little over Indonesia There has been some active convection over Philippines. No TC as yet, however, the risk remains moderate to high in this region this week.
In the past week there was a squash zone over the Marquesas area but trade winds were below par over remainder of South Pacific.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ rebuilt last week from Solomons to Suwarrow and there was a convergence zone around the centre of a low that formed near 30S to South of Southern Cooks.
This week the SPCZ is expected to intensify and move south, reaching from Samoa to Papeete by Tuesday then splitting and relaxing over French Polynesia but shifting south in-between Vanuatu and Fiji on Thursday and forming a LOW between Fiji and NZ on Friday that then rapidly moves SE and deepens to east of NZ by Saturday 10 August .

Sub-tropical Ridge STR
High cell in the STR to east of NZ is currently 1035+ near 45S and expected to weaken back to below 1030 by Wednesday. To west of 180 STR is reforming along 30S and remains weak, so that there is no squash zone in the trade winds to the north.

Roaring 40s and New Zealand
W/NW flow over NZ on Monday and Tuesday, and a trough crossing NZ on Wed to Friday, then a Low is expected to deepen to NE of NZ on weekend Sat/Sun 10/11 Aug UTC with a weak ridge over NZ.

Route Briefings
Tahiti to Tonga:
Wait until the trough clears Tahiti and the winds revert to be from S/SE either on Tuesday or Wednesday. The next trough is expected to cross Aitutaki on Tues 13/14 Aug, so it may be better to go via Suwarrow.

Between NZ and Fiji/Tonga
Keep an eye on that Low from Fid 9 to Sun 11 Aug.

See my yotpak at http://lnk.ie/HS6A/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/HS6B/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/HS6C/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/HS6D/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

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