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

28 April 2013

BOBGRAM issued 28 April 2013

WEATHERGRAM

YOTREPS

Issued 28 Apr 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.

The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) is based on the standardized difference in the barometer readings between Tahiti and Darwin. It sums up the weather pattern over the South Pacific as one number. SOI has been erratic this year and on 27 April it was plus 0.44.

The Ocean: Sea surface temperatures SST across the equatorial Pacific may be thought of as a thermostat for the planetary weather engine. The warmer the sea the quicker it evaporates, tossing water vapour into the air, and when this vapour rises then it cools into cloud. The Pacific region hosts the warmest sea on the planet so its abnormalities tend to influence changes in clouds around the equator and these in turn tweak the latitude zones of weather around the planet.
During March there was a warming trend in the SEEP (surface of the eastern equatorial pacific) but this revered during April. So there is a neutral signal also coming from the Ocean.

Madden Julian Oscillation MJO

The MJO is a cycle of enhanced tropical convection that occasionally moves from Indian Ocean across Australia into the Coral Sea, and it can trigger the formation of Tropical cyclones, as happened in early March. There has been a weak MJO event moving into the pacific region over the past few weeks, and in the past week there has been signs of increased activity in the South Pacific Convergence Zone.

CRUISING ROUTES
Panama to Galapagos: There could be some useful NW/NE winds for departure on Monday 29 April, then local winds should be light or southerly until around 5 May. The International Convergence Zone ITCZ is weaker than last week and mainly located between 8N and 2N and mainly to west of 80W.

Galapagos to Marquesas: There are signs of a convergence zone between 120 and 130W but this is getting weaker. Some good trade winds over Galapagos and these should last for a week of so making this a good time to go. To get the most from wind and surface current head off for 6S110W and follow current to 7S124W and then go direct to Marquesas.

NZ to the Tropics.
The nominal start of the cruising season is 1 May, and that's an OK day to go but with rather light winds from a passing ridge. Those departing then will encounter a passing trough on Friday/Saturday, and it should be an OK adventure. A good time to depart is with fading SW winds as on Monday/Tuesday 29/30 April or on Sun 5 May.

WEATHER ZONES
South Pacific Convergence Zone SPCZ

The South Pacific Convergence Zone SPCZ is very active and broad from Solomons to between Vanuatu and Fiji. Fiji Met Service have found a tropical depression under those clouds SW of Solomons and upper air conditions are good for this feature to go west. The Fiji Met Service map also illustrates a good example of a squash zone of enhanced trade winds between the SPCZ and the STR. Avoid.

Another feature is expected to deepen into a Low over Fiji/Tonga area over Monday Tuesday and then gather the energy of SPCZ and take it SE. If you are cruising between NZ and Tahiti then it will be best to go clockwise around this low.

Sub-tropical Ridge STR

The Sub-tropical ridge-STR, the zone dividing the SE trade winds from the roaring 40s, is well north of its normal position over Australia/NZ, but not so to east of NZ. Those who are cruising between NZ and Tahiti may still be waiting for STR to come north.

High that, on Sunday, was over eastern Australia is expected to cross Tasman Sea on Tuesday and NZ on Wednesday and then go east of NZ along the STR, making a squash zone of easterlies between it and the Low from Fiji. Avoid.

Roaring 40s and New Zealand

An active trough is expected to cross the Tasman Sea on Wednesday move onto South island on Thursday and be followed by a cold SW flow over NZ on Saturday. Avoid.

After that another High should cross Tasman Sea/NZ on Sun 5 May and Monday 6 May .

FOR MORE

See my yotpak at http://lnk.ie/F2T8/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.

Weathergram with graphics is http://lnk.ie/F2T9/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com

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21 April 2013

BOBGRAM issued 21 April 2013

WEATHERGRAM
YOTREPS
Issued 21 Apr 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.

The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) is based on the difference in the barometer readings between Tahiti and Darwin. It sums up the weather pattern over the South Pacific as one number. SOI has been erratic this year and on 20 April it was plus 0.62.

The Ocean: Sea surface temperatures SST across the equatorial Pacific may be thought of as a thermostat for the planetary weather engine. The warmer the sea the quicker it evaporates, tossing water vapour into the air, and when this vapour rises then it cools into cloud. The Pacific region hosts the warmest sea on the planet so its abnormalities tend to influence changes in clouds around the equator and consequent changes in the latitude zones of weather around the planet.
During March there was a warming trend in the SEEP (surface of the eastern equatorial pacific) but this has reversed during April. So there is now a neutral signal also coming from the Ocean.

Madden Julian Oscillation MJO
The MJO is a cycle of enhanced tropical convection that occasionally moves from Indian Ocean across Australia into the Coral Sea, and it can trigger the formation of Tropical cyclones, as happened in early March. There was a weak MJO event moving into the pacific region over the past few weeks, with little impact. The next MJO cycle is likely to occur around mid–May.

Panama to Galapagos: There could be some useful NW/NE winds for departure from Tue 23 April, but anticipate a lot of motoring in light winds. Some help may be gleaned from a surface current by going counter-clockwise around Isla Mapelo. The International Convergence Zone ITCZ is stronger than last week and mainly located between 8N and 2N and mainly to west of 80W.

Galapagos to Marquesas: There are signs of a convergence zone between 122 and 132W but this is expected to fade during the coming week. Some good trade winds over Galapagos for a change and these should last for a week of so making this a good time to go. To get the most from wind and surface current head off for 1 deg 50min S 100W and then 4 deg 30min S 108 W and then go direct to Marquesas.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The South Pacific Convergence Zone SPCZ is draped from the east end of the Solomons across Fiji/Samoa to the Southern cooks. A tropical Low MAY form over the area west of Fiji around Sun 28 April and then deepen as it moves SE on Mon/Tue 29/30 April. Still too early to tell at this stage, so be watchful.

Sub-tropical Ridge STR
The Sub-tropical ridge-STR, the zone dividing the SE trade winds from the roaring 40s, has been forced to the north for a while, allowing a westerly flow to reach northern NZ. This is just right for those wanting to sail east of NZ to Tahiti or Southern Cooks. The window is only expected to last until around Thursday 25 April and then a high cell is expected to dip south to 30/40S to east of NZ, killing the wind on this route. So be quick for this.

Roaring 40s and New Zealand
A complex family of low pressure centres area in the Tasman Sea and NZ area at present. This system has been able to direct some moist air from the tropics onto northern NZ recently. This moisture has fed some thunderstorms resulting in surface flooding in Tauranga, landslides in Waihi (west Bay of Plenty) and a tornado + wind damage in Raglan (Waikato west coast). The system seems to have run out of tropical air now and by Wednesday its main low (L1 in above map) should be east of the South Island. The last of the family L2 above is expected to turn into a trough and cross the North Island on Thursday 25 April (ANZAC Day, a public holiday in Australia and NZ).

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

14 April 2013

BOBGRAM issued 14 April 2013

WEATHERGRAM
YOTREPS
Issued 14 Apr 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.

Jeanne Socrates, the 70 year old solo circumnavigating grandma, is now moving into the central Tasman Sea on her way back to Vancouver. I'm watching the weather with her and we think that a low in the Tasman can be avoided OK. Check her story at http://lnk.ie/ENP0/e=bobmcd1.weathergram@blogger.com/http://synereida.livejournal.com/


The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) is based on the difference in the barometer readings between Tahiti and Darwin. It sums up the weather pattern over the South Pacific as one number. SOI has been erratic this year and in mid-April it was plus 0.53, and trending down or relaxing.

The Ocean: Sea surface temperatures SST across the equatorial Pacific may be thought of as a thermostat for the planetary weather engine. The warmer the sea the quicker it evaporates, tossing water vapour into the air, and when this vapour rises then it cools into cloud. This region hosts the warmest sea on the planet so its abnormalities tend to influence changes in clouds around the equator and consequent changes in the latitude zones of weather across the whole Pacific.

During March there was a warming trend in the SEEP (surface of the eastern equatorial pacific) but this has revered during April. So there is a neutral signal also coming from the Ocean, neither LA NINA nor EL NINO.


Madden Julian Oscillation MJO
The MJO is a cycle of enhanced tropical convection that occasionally moves from Indian Ocean across Australia into the Coral Sea, and it can trigger the formation of Tropical cyclones, as happened in early March. The next MJO cycle is about to move into the Coral Sea area over the next few weeks… but is much weaker than the last one. This MJO has already been associated with one cyclone in the Indian Ocean- IMELDA now weakening near La Reunion Island, and there IS TIME for one more in the Pacific before we close this Cyclone season.


Panama to Galapagos: The N/NE winds that are around Las Perlas at present are expected to fade away early in the week followed by light head winds- no good for sailing. Next lot of NE winds is, at this stage, expected to start arriving around Sunday 21 April- but be less than 10 knots. The International Convergence Zone ITCZ is weak and mainly located between 5 and 2N and mainly to west of 85W, easy enough to avoid.


Galapagos to Marquesas: Not much left of that convergence zone that was around 5S 90W last week. Still light head winds for starters, motor off to SW until trade winds are found for sailing near 2S 95W then sail to around 5S 112W then ride a surface current to 7S125W then go direct. From around next weekend there may be a period of SE trade winds over Galapagos- good for sailing the whole trip!

BLOCKING
MetService and NIWA have pointed out the preponderance of blocking anticyclones in the NZ area so far this year as being associated with some weird seasonal weather (wet over eastern Australia and dry over NZ). See http://lnk.ie/ENP1/e=bobmcd1.weathergram@blogger.com/http://metservice.com/rural/seasonal-forecast-north-island and http://lnk.ie/ENP2/e=bobmcd1.weathergram@blogger.com/http://www.niwa.co.nz/climate/sco/seasonal-climate-outlook-april-june-2013 The intensity and permanence of these anticyclones are both beginning to weaken as can been seem from a time-longitude plot of the Southern Hemisphere blocking index, so outlook is for things during the slide into winter to be closer to normal than summer was.


WEATHER ZONES
South Pacific Convergence Zone SPCZ
The South Pacific Convergence Zone SPCZ has sorted itself out during the past week and is now extending from Papua New Guinea to Vanuatu to Fiji to Samoa to Southern Cooks, with another CZ Convergence Zone over French Polynesia.

Sub-tropical Ridge STR
The Sub-tropical ridge-STR, the zone dividing the SE trade winds from the roaring 40s, is showing signs of drifting north, as is normal after the equinox. Compare its current position with where it was in February (see http://lnk.ie/ENP3/e=bobmcd1.weathergram@blogger.com/https://metbob.wordpress.com/2013/02/).

A new HIGH is expected to move east across the Australian bight and then across Tasmania on Friday 19 April and then across central NZ on Mon 22 April. There MAY BE some good voyages from NZ to the tropics as this High moves off to the east of NZ

Roaring 40s and New Zealand
There are two subtropical lows, L1 and L2. L1 is moving SE across the Tasman Sea and is expected to cross central NZ on Tuesday and Wednesday 16/17 April. Then some chilled air on the west side of a Low in the Southern Ocean (L3) is expected to spread northeast-wards across New Zealand and when this air meets with sub-tropical air over the North Island a secondary low should deepen on Friday and Saturday 19/20 April, along with a cold shock of southerly winds.

L2 is near 30S 170W and expected to have an easier track to the south then southeast, peaking on Wednesday like L1 but fading before it gets south of the STR.

See my yotpak at http://lnk.ie/ENP4/e=bobmcd1.weathergram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/ENP5/e=bobmcd1.weathergram@blogger.com/http://metbob.wordpress.com
Weathergram text only http://lnk.ie/ENP6/e=bobmcd1.weathergram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/ENP7/e=bobmcd1.weathergram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

07 April 2013

BOBGRAM issued 7 April 2013

WEATHERGRAM

YOTREPS

Issued 07 Apr 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.

The Atmosphere: The Southern Oscillation Index SOI (30 day running mean) is based on the difference in the barometer readings between Tahiti and Darwin. It sums up the weather pattern over the South Pacific as one number. SOI has been erratic this year and on 31 March it was plus 0.78.

The Ocean: Sea surface temperatures SST across the equatorial Pacific may be thought of as a thermostat for the planetary weather engine. The warmer the sea the quicker it evaporates, tossing water vapour into the air, and when this vapour rises then it cools into cloud. This region hosts the warmest sea on the planet so its abnormalities tend to influence changes in clouds around the equator and consequent changes in the latitude zones of weather across the whole Pacific.

Well, in the past month the SST in this target zone has been warming in the east and about neutral near the 180 line. There is possibly a trend towards El Nino (warm seas) starting in the ocean. This is at odds with what is happening in the atmosphere.

Madden Julian Oscillation MJO

The MJO is a cycle of enhanced tropical convection that occasionally moves from Indian Ocean across Australia into the Coral Sea, and it can trigger the formation of Tropical cyclones. In early March an MJO moved into the Coral Sea and helped trigger TC SANDY and TIM. This MJO has since faded away and the next cycle may not arrive until mid or late April—so Island- hopping in the South Pacific over next few weeks may be OK.

WEATHER ZONES

Panama to Galapagos: The NE winds that were around Las Perlas last week have gone now, and winds this week south of the continental shelf at 7N are mainly light and from the SW. Not good for sailing. The International Convergence Zone ITCZ is weak and mainly located along 3 to 4N and one part of it is active at present near 4N 82W, so stay east and south of there.

Galapagos to Marquesas: There is still some remains of a convergence zone along 5South, with one area of convergence near5S 90W. The best sailing path at present is to head off to the SW to around 4S 95W and around there to latch into trade winds all the way to Marquesas.

South Pacific Convergence Zone SPCZ
The South Pacific Convergence Zone SPCZ has increased during the last week, and now is an amalgam of several convergence zones, with most of them being in the Coral Sea and one of them extending across Tuvalu to Southern Cooks and another from northern Vanuatu to Fiji/ northern Tonga. There are a few more CZ convergence zones in the Coral Sea and a tropical low is expected to form there off the north Queensland coast by Thu/Fri 11/12 April and then travel southeast out of the Coral Sea and across the Tasman Sea on Sun/Mon 14/15 April and central NZ on or around Tue 16 April. Avoid.

Sub-tropical Ridge STR
The Sub-tropical ridge-STR, the zone dividing the SE trade winds from the roaring 40s, is showing signs of drifting north, as is normal after the equinox. It is oscillating between 40/45S and 35S/40S. The high which is in the Aussie Bight tonight is expected to travel south of Tasmania and around the south coast of the South Island on Tue 9 April. This high is then expected to move NE across NZ on Wed to Fri 10/12 April and then off to the east/SE.

Roaring 40s and New Zealand
On Tuesday and Wednesday a S/SE wind change with a cold front is expected to move north over NZ. The next front is likely on Thurs/Fri/Sat 11/12/13 April preceded by a strong NW flow and followed by west/SW winds.

See my yotpak at http://lnk.ie/EFG8/e=bobmcd1.weathergram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/EFG9/e=bobmcd1.weathergram@blogger.com/http://metbob.wordpress.com
Weathergram text only http://lnk.ie/EFGA/e=bobmcd1.weathergram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/EFGB/e=bobmcd1.weathergram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

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