Translator

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

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
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<
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.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<
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.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<
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):

>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
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.
>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<


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/ .

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<


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/ .

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>><<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
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

Blog Archive