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

30 June 2013

BOBGRAM issued 30 June 2013

WEATHERGRAM
YOTREPS
Issued 30 June 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 rose to over plus 1 briefly in April, dropped to minus 0.39 in early May, and has since then bounced back positive, maintaining a value over reaching 1 for most of June and at 1.06 on 30 June. So the signal coming from the Atmosphere at present is hinting at a La Nina.


The Ocean: 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 equatorial Pacific region hosts the warmest sea on the planet. Thus the Sea surface temperatures SST across the equatorial Pacific 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 these in turn tweak the latitude zones of weather around the planet. So far this year NINO3.4 has been on the cool side, but not strongly so, and continues in this trend. Certainly not as cool as in the big recent La Nina events in 2010/11 and 2011/12.


Tropical cyclones and Monsoon
Two tropical cyclones around at present. DALILA going northwest off the west coast of Central America, and RUMBIA which has just crossed the Philippines and is heading for China making landfall about 126 n miles west of Hong Kong. The Monsoon rain has still been heavy in north central India and over Bay of Bengal, but hasn't yet reached the bush fires of Indonesia.


WEATHER ZONES
A look at the air pressure anomaly map for mid-May to mid-June reveals lower than normal pressures over Europe, Eastern Russia, and the Tasman Sea. It also shows that the STR in the southern hemisphere is shifted a little to the south and stronger than normal (except across the Tasman Sea).

South Pacific Convergence Zone SPCZ
The SPCZ is extending eastwards along 5-10S, at the northern end of its range. By Wednesday the forecast is that there may be two smaller convergence zone extensions CZ, one from eastern Coral Sea to New Caledonia and t'other over French Polynesia. These CZ branches are expected to be liked with Lows at 35S and should be avoided. The one over New Caledonia is expected to weaken and move onto Fiji on Friday or Saturday.

Sub-tropical Ridge STR
The STR has recovered from last week and is reasonably strong along 30 to 40S, but remains weak in the Tasman Sea. So the large High that is over Eastern Australia by Wednesday is expected to weaken as it crosses the Tasman Sea on Thursday and just bring one day of light winds to northern NZ on Friday.

Roaring 40s and New Zealand
In NZ this week the action mainly comes from a low that is expected to form to north of Lord Howe on Monday and then cross northern NZ on Wednesday. This is likely to be followed by a broad trough bring a NW flow to NZ on Saturday, a SW flow on Sunday and then a possible weather pattern for good departures from NZ to the tropics on Monday 8 July.

Tahiti to Tonga:
Between Monday and Wednesday UTC there is a CZ affecting Tahiti. On Thursday to Saturday there are expected to be enhance trade winds on the north side of a large high moving east along 30S. Better to wait for Sunday 7 July.

Sad about SV NINA
A crew member called me via sat phone from SV NINA during afternoon on Monday 3 June, when they started to encounter a NW gale and wanted to know where best to go. I got them to call me back in 30mins, downloaded some weather data and, when they called back, passed on a forecast, then sent it by txt and email to their sat phone.
They were caught is a rapidly deepening Low. It was too late to run for cover- that would just prolong the incoming storm , so I suggested they go south a bit then hove to and brace for a period of storm force southerly winds followed by a period of swells around 7 or 8 significant metres.
On Tues 4 June they sent me one more txt position via sat phone but since then there has been no coms. Discussing our concern with friends and family and the fact that the emergency beacon on NINA has not yet been deployed,--- so radio searches were done until their last likely ETA in Australia arrived last Sunday. Then, with concern exceeding expectations, Rescue Coordination Centre has done a full plane search and coastal search. So far this has been negative. We still have our fingers crossed for them.

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

23 June 2013

BOBGRAM issued 23 June 2013

WEATHERGRAM
YOTREPS
Issued 23 June 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 rose to over plus 1 briefly in April, dropped to minus 0.39 in early May, and has since then bounced back positive, reaching 1.2 from 9 to 16 June, and relaxing to 0.8 by 23 June. So the signal coming from the Atmosphere has been erratic and at present is hinting at a La Nina.


The Ocean: 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 equatorial Pacific region hosts the warmest sea on the planet. Thus the Sea surface temperatures SST across the equatorial Pacific 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 these in turn tweak the latitude zones of weather around the planet. So far this year NINO3.4 has been on the cool side, but not strongly so, and continues in this trend.

Tropical cyclones and Monsoon
No tropical cyclones around at present. The Monsoon has been generally quieter than normal for the past month over India but a deluge over RUDRAPRAYAG in northern India has recently produced damaging landslides.
The monthly rain anomaly map clearer shows a pole-ward shift of the ITCZ. This is a La Nina trait.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is extending eastwards along 15S, with a branch over Vanuatu and another over Northern cooks to French Polynesia. The branch that is likely to be over Vanuatu until mid-week is expected to move east across Fiji and Tonga by the end of the week on Fri/Sat 28/29 June.

Sub-tropical Ridge STR
All that remains of the STR east of 180 is a thin line mainly along 25 to 30S.
A new high cell with central pressure over 1030 is moving east over Tasmania tonight and is expected to be deflected southeast to south Tasman by Wednesday 26 June and then northwards so that it may cross the North Island on Sat/Sun 29/30 June.

Roaring 40s and New Zealand
The eggbeater southerly that was mentioned in last week's Weathergram was a remarkable Low, bringing snow for several days to the South Island so that there are now 1 to 2 metre drifts of snow on the upper Canterbury plains. Rain caused landslides in Dunedin and flooding in Christchurch, Wellington had a stormy night and swells rose to significant height of 7 metres (occasional 11 and maximum 15 metres) thru Cook Strait, and Auckland had some lightning and hail damage. The swells rotating around this system have reached Fiji/Tonga/Niue (surfs up) and are expected to reach Southern Cooks on Monday and French Polynesia around Tuesday/Wednesday –and these may well be exacerbated by spring tides on 24th to 26th June of tonight's perigean FULL MOON tonight (some call it a super moon, and it is indeed the largest looking of 2013). Check it out if you can.

This week another low is expected- but this time it is forming NORTH of the STR rather than in the southern ocean. Its clouds are already spinning off the east Australian Coast and it is expected to move quickly along 30S- reaching 180 by Thursday 27 UTC. Another may form in the Tasman Sea next Monday 1 July and travel more slowly eastwards.

Route weather picks
Tahiti to Tonga:
The swells from the SW should ease again after Wednesday. The SPCZ is expected to cross southern parts of this route from Sunday 30 to Tuesday 2 July. SO If you go, take the northern route via Suwarrow.

NZ to the Tropics.
A dying southerly on Monday and light winds on Tuesday- but if you depart on these days you are likely to encounter strong head winds on Tuesday night and Wednesday. A more comfortable voyage may happen with a Thursday departure, as this should get far enough North by mid-next-week to avoid the next low.

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

16 June 2013

BOBGRAM issued 16 June 2013

WEATHERGRAM
YOTREPS
Issued 16 June 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 rose to over plus 1 briefly in April, dropped to minus 0.39 in early May, and has since then bounced back positive, reaching 1.2 from 9 to 16 June. So the signal coming from the Atmosphere has been erratic and at present is tending towards La Nina.

The Ocean: 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 equatorial Pacific region hosts the warmest sea on the planet. Thus the Sea surface temperatures SST across the equatorial Pacific may be thought of as a factor in the running of planetary weather engine. Its abnormalities tend to influence changes in clouds along the equator and these in turn tweak the latitude zones of weather around the planet. In the past month there has been a growing area of cooler than normal conditions over the eastern equatorial Pacific. This is a possible sign of a trend towards La Nina conditions, but we still do not have enough evidence to say this trend will continue.

Tropical cyclones
No tropical cyclones around at present, but there is a tropical Low in NW Pacific, and this is the region with the highest risk of formation during the coming week.
The outlook for later in June is for the heavy rain that is now over India/Singapore to migrate eastwards.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is stretched thinly along 10S, with a small branch between Vanuatu and Fiji that is fading, and another branch over French Polynesia that is linked to a Low that is expected to form near 30S 140W and then move southeast.

Sub-tropical Ridge STR
Highs within the STR are weak at present. The high that is likely to be over Tasmania on Wednesday 19 June is expected to weaken away in the Tasman Sea on Thursday.

Roaring 40s and New Zealand
Warm front of a large low system crossed NZ over the weekend. The Low is expected to have multi centres and it crosses NZ mid-week, bringing SW squally gales to the area north of NZ.

On Thursday the Low centre is expected to be east of NZ and this should combine with the weakening high then in the south Tasman Sea so that these systems act like an eggbeater focusing cold strong southerly winds fresh from the chill of the southern ocean to the midriff of NZ.

Route weather picks
Tahiti to Tonga:
Looks like a good week to go, with a quiet SPCZ, but will need to take the northern route via Suwarrow to get a useful trade wind.

NZ to the Tropics.
The mid week gale over northern NZ makes this a 'stay-at-home' week. Maybe ok to depart northern NZ again on Friday or Saturday 21/22 June.

See my yotpak at http://lnk.ie/GH58/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/GH59/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/GH5A/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/GH5B/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com

Feedback to bob@metbob.com

09 June 2013

BOBGRAM issued 9 June 2013

WEATHERGRAM
YOTREPS
Issued 09 June 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 rose to over plus 1 briefly in April and dropped to minus 0.39 in early May and bounced back into the positive in May, and has now reaches plus 1.3 on 9 June. So the signal coming from the Atmosphere has been erratic and at present is tending towards La Nina.

The Ocean: 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 equatorial Pacific region hosts the warmest sea on the planet. Thus the Sea surface temperatures SST across the equatorial Pacific may be thought of as a factor in the running of planetary weather engine. Its abnormalities tend to influence changes in clouds along the equator and these in turn tweak the latitude zones of weather around the planet. In the past month there has been a growing area of cooler than normal conditions over the eastern equatorial Pacific. This is a possible sign of a trend towards La Nina conditions, but we still do not have enough evidence to say this trend will continue

ITCZ and TC
ITCZ had strengthened across the Pacific. TC ANDREA was the first TC for the Gulf to the Atlantic this year and left a very marked path on the rainfall accumulation map. TC YAGI has formed in NW Pacific and is heading for Japan.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is gathering strength along 10S at present and may drift south onto temporarily across Vanuatu and Fiji on Thursday and Friday 13 and 14 June.

Sub-tropical Ridge STR
Large High travelling east along 40/45S well east of NZ has a strong squash zone of enhanced trade winds on its northern side tonight with swells over 5 metres.
High in the Tasman Sea is weak and is having its travel restricted; it should finally cross NZ on Fri/Sat 14/15 June. Its squash zone SZ is only in the Coral Sea.
Large high is southern Aussie bight is travelling along 45 to 55 S and should pass by south of NZ on Mon 17 June, preceded by very cold southerly winds onto southern NZ on Sun 16 June.

Roaring 40s and New Zealand
Between the Highs we have lows, and the one crossing northern NZ tonight is expected to the go SE and expand to cover a wide area east of NZ by Wednesday.
The one over Australia on Wednesday is expected to go SE into the Tasman, deepening rapidly on Thursday (avoid) and Friday in the Tasman and then be deflected NE across Northern NZ by Sun/Mon/Tue 16/17/18 June -- something like a near weekly trough cycle for NZ at present.

Route weather picks
French Polynesia to points west: There may be complications from the SPCZ between Southern cooks and Niue from Tuesday 11 to Sun 16 June--- could be a better voyage next week.

NZ to the Tropics.
Mon to Thursday are looking to be good days to go with a steady SW flow.
The weak winds of a passing ridge on Friday and northerly winds of an incoming trough on Sat/Sun 15/16 June are not good.

See my yotpak at http://lnk.ie/GA26/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/GA27/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/GA28/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/GA29/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

02 June 2013

BOBGRAM issued 2 June 2013

WEATHERGRAM
YOTREPS
Issued 02 June 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) is based on the standardised difference in the barometer readings between Tahiti and Darwin. It sums up the weather pattern over the South Pacific as one number.
SOI rose to over plus 1 briefly in early April and dropped to minus 0.39 in early May and bounced back into the positive in May, and reached plus 0.83 on 31 May. So the signal coming from the Atmosphere has been erratic and at present is tending towards La Nina.

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 equatorial Pacific region hosts the warmest sea on the planet so its abnormalities tend to influence changes in clouds along the equator and these in turn tweak the latitude zones of weather around the planet.

In the past month there has been a growing area of cooler than normal conditions over the eastern equatorial Pacific. This is possibly a sign of a trend towards La Nina conditions, but we still do not have enough evidence to say this trend will continue

ITCZ and Monsoon
ITCZ is strong across the Pacific. Monsoon has arrived in Kerala, SW India, on 1 June. It is on time and seems to be more active than normal at this stage. It is expected to reach Delhi by 29 June. Also active convection for Sea of Bengal.
This marks the end of the 2013 Everest climbing season (with 8 fatalities). Everest was first climbed on 29 May 1953 by Tenzing and Hillary, and news of this was made public on 2 June 1953 at QEII coronation 60 years ago today. We in NZ are having a public holiday on Monday and you should too!

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ moved southwards over Vanuatu and Fiji last week, resulting in the Low that is tonight near 28S 178W and moving off the SE reaching 44S 150W by 05 0000UTC. This Low has drained a lot of convective energy from the tropics.
This week the SPCZ is weak and recovering as scattered lumps of convection mainly along 10S.

Sub-tropical Ridge STR
The next HIGH in the STR is currently in the Australian Bight and is expected to cross eastern Australia on Monday and Tuesday and then the Tasman Sea on Wednesday and Thursday reaching North Island on Friday 7 June.

Roaring 40s and New Zealand
This week the STR is weak in the NZ longitudes and this allows the trough crossing NZ to blossom into a large Low over the North Island by Tuesday. Avoid.

Route weather picks
Galapagos to Marquesas: Good to go this week. We have light to moderate South to southeast winds over Galapagos and moderate trade winds trade winds from 2S onwards.

NZ to the Tropics.
Wait for the trough to move away from the North Island. There may still be some squally SW winds around on Wednesday, but Thursday may be good to go. Friday/Saturday/Sunday could have winds too light in the passing high. Next front to reach Northland is likely on Monday/Tuesday 10/11 June, closing the window.
So the best day to go from Northland this week is Thursday.

See my yotpak at http://lnk.ie/G3GU/e=bobmcd1.bobgram@blogger.com/http://www.boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is http://lnk.ie/G3GV/e=bobmcd1.bobgram@blogger.com/http://metbob.wordpress.com
Weathergram text only and translator is http://lnk.ie/G3GW/e=bobmcd1.bobgram@blogger.com/http://weathergram.blogspot.co.nz
Website http://lnk.ie/G3GX/e=bobmcd1.bobgram@blogger.com/http://www.metbob.com
Feedback to bob@metbob.com

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