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

16 July 2017

Bob blog 16 July 2017

WEATHERGRAM
YOTREPS
Compiled Sun 16 July 2017

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.

TROPICS
Tonight HURRICANE FERNANDA is travelling west-northwards away from the Mexican west coast. And it is being followed by a tropical depression.
It is vaguely heading towards Hawaii, but at its current pace will not reach those longitudes until 24 July and is likely to fade away by then.
And there is TALAS in the China Sea. The models are picking it may travel west across SE Asia , but will probably fade away inland. Cyclone tracks may be seen at https://ruc.noaa.gov/tracks/

Last week's rain map, compared with the week before, from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, shows an enhancement in the rain in Solomon islands, and relaxing rain along the ITCZ.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
The SPCZ starts this week reasonably active around Solomon Islands, and is expected to slowly weaken during the week.
A passing trough, associated with a front in the Southern Ocean, is expected to go east across New Caledonia area on local Thursday and then move onto the Tongan area on local Saturday preceded by NE winds and followed by southerlies.

Subtropical ridge (STR)
HIGH located over Northern NZ tonight is expected to travel east along 33s to east of NZ this week. It may build to over 1040 when it gets east of 140W after Friday and the should have a squash zone strong SE winds and over 3m swell on its northern side, around the Gambier Islands.

Australia to New Caledonia:
A trough is expected is to travel east across the eastern seaboard on Tuesday night local, followed by strong SW winds and large swells on Wednesday. It should be ok to depart on Thursday but the voyage will need to go ese at first and allow for ESE wind after 158E.

Departing northern NZ to the north or east for the tropics:
North to NW winds over northern NZ until a cold front crosses the area on Wednesday/Thursday. It may be ok for departure on Friday if you don't mind SW winds and 3 metres swells. Otherwise better to wait until Saturday.

French Polynesia to the west:
This looks to be a good week to go west. The SPCZ is weak and the subtropical ridge is not expected to produce much of a squash zone on this path - however you may get swell over 3 metres on Thursday UTC.
If you would like more detail for your voyage, then check metbob.com to see what I offer.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my website http://www.metbob.com for more information
Feedback to bob@metbob.com or txt 6427 7762212
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
Click FOLLOW at bottom right to subscribe.
To unsubscribe send a reply email saying LEAVE.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

09 July 2017

Bob blog 9 July

WEATHERGRAM
YOTREPS
Compiled Sun 9 July 2017
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.

Last month (June)
Sea Surface temperature anomalies may be seen at http://www.ospo.noaa.gov/data/sst/anomaly/2017/anomg.7.6.2017.gif
and show that there continues to be more area covered by warm anomalies than by cool anomalies. And there is still a warm river appearing along east coast of South America.
To see how the annual weather cycle and the seasons are working out, take a look at the average isobar maps from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html
In June, the subtropical ridge in the southern hemisphere has travelled NORTHWARDS. This trend is subtle and can be seen in the isobars around NZ. The STR is strong in the Indian Ocean. Looking at the anomalies, the large continuous red area from south Indian Ocean to South Australia/NZ to east of NZ in the South Pacific, shows that the STR has been covering more latitudes than normal, and encouraging blocking highs --- explaining the dry winter in Australia.
The small green anomaly in the North Tasman Sea shows that was a favoured spot for lows to deepen in June, bringing many cyclone NE winds to northern NZ, bringing wet conditions.
The wetter than normal conditions over northern NZ also shows in the monthly rain map. This monthly rain map shows heaviest rainfall in spots from Myanmar across southern China to South Japan, and over Solomons. Last 30 days of rainfall, and its anomaly, are seen at trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html

TROPICS
Deluging rain associated with TC NANMADOL brought damaging landslides to Japan, with a death toll of at least 15 people. See phys.org/news/2017-07-nasa-tropical-cyclone-nanmadol-japan.html
Tonight HURRICANE EUGENE is travelling northwest off and parallel to the Mexico west coast.
Last week's rain map from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif
shows an enhancement in the rain in the ITCZ over Eastern Pacific, and relaxing rain in other areas.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
The SPCZ starts this week reasonably active from Solomon Island to the Tuvalu/Tokelau area, and is expected to weaken during the week.
A passing trough, associated with a front in the Southern Ocean, is expected to go east across Rarotonga area on Tuesday UTC. Another passing trough may reach New Caledonia area around Wednesday UTC and then move onto the Tongan area on Thursday UTC and may bring some NE/N winds to Niue on Friday 14 July UTC and Rarotonga on Sat 15 UTC.

Subtropical ridge (STR)
HIGH is expected to slide southeast off Australia and into the South Tasman Sea on local Wednesday and then southeast past the south of NZ on local Friday. Another HIGH, rather weak, is expected to drift odd east Aussie on Friday local and move onto northern NZ around local Sunday 16 July.

Australia to New Caledonia:
For much of this week, this voyage is between the HIGH over Australia and low pressures over NZ, so it is mainly a disturbed SW/S/SSE flow to New Caledonia, but with wind holes in passing weak ridges.
Late in the week a trough is expected to reach Brisbane area by Sat 15 July local and that should be followed by a weather pattern offering a better sailing breeze for this trip.

Departing northern NZ to the north or east for the tropics:
On Monday, decreasing SW flow over northern NZ, and a brief break in the weather there on Tuesday may allow voyages to escape to Tonga, but not to Fiji or New Caledonia.
On Tuesday, a cold southerly is expected to reach the South Island following a trough. By Wednesday, this trough is expected to deepen into a low over the North Island and linger until it finally travels off to the east on Friday. Although this low is only being fed by southerlies from around 50S, it is cold enough to be a notable winter low with rough seas and swells over 4 sig metres north of NZ on Thursday, so may as well stay put and let it pass.

French Polynesia to the west:
There is a weak passing trough over Society Islands on 10/11 Monday/Tuesday local. This is preceded by a NW flow and followed by SE to E winds. It may be better to wait until after this trough for departure to the west.
This passing trough is likely to reach Palmerston Island by around local Monday, so wait there until local Tuesday for departure.
Another passing trough is expected to reach Niue area on local Thursday 13 July with NE winds. Avoid being there then or moor well.
If you would like more detail for your voyage, then check metbob.com to see what I offer.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my website http://www.metbob.com for more information
Feedback to bob@metbob.com or txt 6427 7762212
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
Click FOLLOW at bottom right to subscribe.
To unsubscribe send a reply email saying LEAVE.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

02 July 2017

bob blog 2 July

WEATHERGRAM
YOTREPS
Compiled Sun 2 July 2017

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.

That was a long blog last week, so here's a nitty-gritty one this week

The Tropics
This week it's Japan's turn for a tropical storm with TC NANMADOL approaching from the southwest.

The last week's rain map
from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif
shows an enhancement in the rain south of the equator in the Indian Ocean, around the coast in China, and about the Solomon Islands, and a decrease in intensity in the Intertropical convergence zone ITCZ.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
The SPCZ stretches as an almost continuous band from Papua New Guinea/Solomons to around Tuvalu/Tokelau. It is expected to stay put this week. The convergence zone over the Society Islands in French Polynesia today is expected to fade away between Society Group and Tuamotu group.

Subtropical ridge (STR)
HIGH that is in the North Tasman Sea on Monday is expected to cross northern NZ on Tuesday and then fade between NZ and Tonga between Wednesday and Friday.
A ridge is expected to remain in the north Tasman sea all week, but next HIGH to the west is NOT expected until next week over eastern Australia tonight is expected to spread into the Tasman Sea by mid-week and then onto central NZ around Thursday and further east this weekend.

Australia to New Caledonia:
May be Ok on a Monday departure, after that the ridge between Brisbane and New Caledonia offers a barrier of light winds for the remainder of the week.

Departing northern NZ to the north or east for the tropics:
An upper trough is crossing the North Island tonight and Monday with squally conditions, so best to stay put Monday.
Best day to escape between weather systems is Tuesday.
Even then there may be some strong winds on Thursday ahead of the next trough from the SW, with 3 occasionally 4 metres swells. These troughy conditions are expected to last until early next week.

French Polynesia to the west:
There is a convergence zone lurking to north of Society Islands on local Sunday, the best day of this week to go west this week is on local Monday in the trade winds that follow that convergence zone.
A passing trough is likely to reach Palmerston Island by around local Thursday followed by northerly winds as another trough lurks off to west of Palmerston Island.
If you would like more detail for your voyage, then check metbob.com to see what I offer.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my website http://www.metbob.com for more information
Feedback to bob@metbob.com or txt 6427 7762212
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
Click FOLLOW at bottom right to subscribe.
To unsubscribe , send a reply email saying LEAVE.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

25 June 2017

Bob Blog 25 June

WEATHERGRAM
YOTREPS
Compiled Sun 25 June 2017
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.

Perigean tides: Take extra care over the next few days as we had a new moon on Saturday and the moon's perigee was on Friday (NZ dates). The close proximity of these exaggerate the tidal forces causing extreme low and high tides. Combine that with onshore swells and lower than normal air pressure, such as at Timaru and there is a chance that waves will wash higher inland at high tide.
Up to date graphs of the sea level are at www.niwa.co.nz/our-science/coasts/tools-and-resources/sea-levels/, the yellow moon marks perigee and purple is for the new moon.

Thanks:
Thanks to PJ at Perceivingacting channel for posting info to my Facebook site last week about the tip on how to edit the earth.nullschool url to change date.
And thanks to Captain Simon Catterson for showing me around the three-masted, square rigged barque Tenacious when it was in Auckland this week. They are providing valuable training around the world, see their web site at www.jst.org.uk

WEATHERGRAMS/YOTREPS:
These weathergrams have been going weekly for over 20 years, making this blog one of the longest surviving on the Internet. The original inspiration for my blog was to help by mate Mike Harris as he started the YOTREPS scheme. I was hoping this would be a way to get yacht weather observations into the view of those meteorologists who compile the marine weather warnings. It has now come to the stage that Mike Harris is seeking to hand the YOTREPS reporting scheme onto a new enthusiast/manager. I am willing to allow my weathergrams to be part of the package.
So here's Mike's request, and if you can see this in your future please get in touch with him straight away.

NEWS ITEM
YOTREPS 20 years of passage Reporting 20/6/2017
Everyone likes to talk about the weather, but for cruising sailors it's more than just a topic of casual conversation. It has a say on where you can go, when you can go and whether you will be comfortable or sick. It is the power in your sails.
Most long term, live-aboards will be familiar with the many amateur and commercial marine radio stations as a source of forecasts. For safety reasons, many also run traffic lists taking daily reports of positions and weather from boats on passage. The volume of data collected is quite considerable and I'd often wondered what happened to it after the net had closed down. On further investigation I found that often it was kept for a short time then dumped. This was not because it had no value, but because it was not prepared to an agreed standard and could not be delivered to forecasters quickly enough for them to make use of it.

For decades commercial vessels taking part on the VOS (Voluntary Observing Ship) scheme have contributed observations to forecast agencies so the idea had president. In some parts of the world, sailing boats may be the only visitors seen, so their reports can be especially useful, but on the other hand they are unlikely to have trained observers and the calibration of their instruments is not assured. For these reason their data is not used to prepare forecasts but as an independent 'reality' check on their accuracy.

In 1995 these were the ideas that in consultation with Bob McDavitt of New Zealand MetService, lead to the formation of YOTREPS. It provided radio net controllers with a program for logging reports and forwarding them to a server for checking, encoding, forwarding to met. Forecasters and plotting on a web page chart along with a text for news and comments. This has been shown to be an enormously popular feature and the reason that many use the service.

The first YOTREPS report was received in 1996 and now has several hundreds of thousands of reports. Many complete circumnavigations and expeditions have been tracked. The largest vessel was the Queen Elizabeth II. and smallest, I am not sure.

A New Future for YOTREPS
The original php script that I wrote for YOTREPS has, except for some brief breaks while upgrading, operated for some 20 years with very little need for attention. Within the past few weeks I have re-written the scripts to run under current versions of PHP, MySQL and Nginx and should be good for some time to come. However a deteriorating health condition has shown me that now would also be a good time to look for a new manager and place in cyber-space for YOTREPS.

Requirements for the new enthusiast are:
1. A deep and committed interest in all aspects of long distance sailing.
2. A good depth of technical experience in radio communications, and computer technology.

An alternative future could be with an organisation such as a yacht club or radio station. Here the management and technical details could shared and in all probability the computer components installed as an adjunct to an existing web site.

YOTREPS provides a position and weather reporting service. It's free and open to anyone, anywhere in the world. You do not need to be a member of any particular club or have any special license to take part. If you think it could have a future with your club or cruising organisation or fit within your own cruising life style as it did with mine, I should very much like to hear your ideas*.

Mike Harris VK7AAA mike@pangolin.co.nz Please first be sure to be familiar with the YOTREPS pages on pangolin.co.nz and
see www.churchilltrust.com.au/media/fellows/Harris_Mike__2005.pdf

FLEET MAPS: One of the many achievements of the YOTREPS website is to give yachts that only have email access the tools to look at the bigger weather picture. In the South Pacific there is a weather feature unlike anything found anywhere else, called the south pacific convergence zone. It behaves like a wriggly dragon and contains squally showers but is almost invisible in the computer grib data, which tend to show it as an area of light variable winds. Cruising yachts need a weather map which shows exactly where this zone is located, and this is exactly what is given in the Fiji Met Service weather maps which are converted into FLEET code. The FLEET code dates back to WWII and was used to send weather maps to the whole fleet via morse code.
This is how the yachts get and view it:
FIRST (before departure) download and install PhysPlot.exe on your PC (no Mac version) from www.pangolin.co.nz/physplot, part of the YOTREPS website.
Then request the Fiji Fleet code by sending an email to query@saildocs.com, no subject needed, with the message "SEND nadi-fleetcode"
(without the quotes).
An email should arrive back. To view the map, save the number-table in that email to your desktop (or somewhere you can find it) as , for example, fleet.txt then open this file with PhysPlot-
This will show the various convergence zones that make up the SPCZ as brown lines. Black lines are isobars and red/blue lines are passing fronts.

The Tropics
Last Thursday (local) Tropical Cyclone CINDY made landfall on the Gulf coast bringing heavy rain from Louisiana to the Florida Panhandle.
The monsoon is making progress across Asia and into China, and recent heavy rain has triggered a massive landslide at Xinmo village in Sichuan province.
The last week's rain map
from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif
shows an enhancement in the rain over China, the Solomon Islands, the Gulf of Mexico (CINDY) and a decrease in activity around Samoa and the equatorial Atlantic.


WEATHER ZONES
SPCZ=South Pacific Convergence zone.
The SPCZ stretches as an almost continuous band from Papua New Guinea/Solomons to around Tuvalu/Tokelau. It is expected to slowly drift south this week, reaching Samoa Islands around Thursday/Friday, and maybe reaching Fiji this weekend or early next week.
A passing trough is expected to cross the southern cooks by Thursday and then the Austral Islands around Friday/Saturday local.

Subtropical ridge (STR)
HIGH that is over eastern Australia tonight is expected to spread into the Tasman Sea by mid-week and then onto central NZ around Thursday and further east this weekend.

Australia to New Caledonia:
Not for much of this week. As that High travels east across the Tasman Sea there is likely to be too much in the way of southeast winds. A low is expected to form in the Tasman SEA from Thursday, and that may allow a reasonable voyage eventually in its wake, too far away to tell just yet.

Departing northern NZ to the north for the tropics:
Looks ok with a departure on Monday or Tuesday with a High in the Tasman sea and a LOW to east of NZ. Only light winds on Wednesday, and after that the voyage is likely to encounter northerly winds ahead of the next incoming low, so not a good idea.

New Zealand to the east (Tahiti)
Maybe ok for departure in the SW winds early this week and then with the lighter winds of the high that is expected to travel east of NZ late this week. There are lows near 30 to 40S at present, and the voyage may be able to ride in the westerly winds north of these lows at around 25S this week.

French Polynesia to the west:
The recent squash zone of enhanced trade winds and over 3m swells is expected to ease off on Sunday/ Monday. There is a passing trough with variable winds and possible showers, reaching the southern cooks by Thursday local, and Society Islands around local Friday/Saturday, and then settled trade winds with average swell heights.

If you would like more detail for your voyage, then check metbob.com to see what I offer.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my website http://www.metbob.com for more information
Feedback to bob@metbob.com or txt 6427 7762212
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
Click FOLLOW at bottom right to subscribe.
To unsubscribe send a reply email saying LEAVE.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

18 June 2017

Bobgram 18 June

WEATHERGRAM
YOTREPS
Compiled Sun 18 June 2017

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.

In last week's blog I mentioned a tip about earth.nullschool.com, that it can be used like a time-machine by using the >> symbol (or do a shift k) to go forward a day, or, to go back a day, click the << symbol (or do a shift j)
Thanks once more to the crew of SV Legacy, we can extend this tip; here's a quicker way to dial up the date we wish to visit:
If you click one of the date arrows in the control menu to change the date or time, the URL will show a date...
Then you can just CHANGE THAT DATE IN THE URL to suit yourself and hit enter. It can be a little confusing as the date in the URL is UTC and the default display in the "earth" menu is local.
There is data stored at the earth.nullschool website from 1 November 2013.

The year is turning;
Solstice is at 0424UTC on Wednesday June 21st. Enjoy.
For those of you who are celestial navigators, little d is zero at the solstice. Yippee.

The Tropics
The monsoon has slowed down to a crawl over the northwest end of India/Pakistan :
Monsoon progress map from www.imd.gov.in/pages/monsoon_main.php

Tropical Cyclone MERBOK gave Hong Kong a pounding last Tuesday night (local) cancelling 41 flights and delaying more than 300.
See www.scmp.com/news/hong-kong/health-environment/article/2097971/observatory-lowers-signal-typhoon-merbok-leaves

Tonight, there are some tropical depressions off the east coast of Central America, and the east coast of South America (north of the equator). These one near Belize is expected to travel north then northeast, and the one near 5N40W is expected to travel off to the WNW towards Honduras.

The last week's rain map shows a stalled monsoon over India and a build-up of convection around Malaysia/ Indonesia to Papua New Guinea. The track of MERBOK can be seen. The intense rain that visited Tuvalu /Tokelau two weeks ago has faded in the past week. And there is a wet low forming in the Tasman sea.

Rain for the past fortnight from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
The SPCZ stretches as an almost continuous band from Papua New Guinea/Solomons to around northern Vanuatu/Wallis/Futuna and then between Southern Cooks and Society Islands. It is expected to travel somewhat to north and east this week, visiting Samoa on Saturday/Sunday UTC then may go south again.

A trough is expected to cross the Austral Islands around Thursday 22 June UTC and then form a low to the southeast of French Polynesia that should travel off to the southeast and deepen. Associated front is expected to cross the Society Islands on Thursday UTC and the Tuamotu Islands on Friday UTC.

Subtropical ridge (STR)
High that is departing NZ on Monday is expected to travel east along 40s to around 160w and then merge with a 1040 hPa high developing in cold air near 50s 150w for a day or so.
Next high is forming over SE Australia on Monday Tuesday, and may have its easterly progress blocked by that Tasman Low and so is expected to travel slowly north and reach the North Tasman sea by the weekend.

Australia to New Caledonia:
There was a good-enough looking opportunity over the weekend for this voyage, riding in the southerly winds on back end of the Tasman Low.
A departure on Monday may encounter strong southerly winds and rough seas for starters and then have a reasonable voyage. A Tuesday or later departure may encounter easterly head winds this weekend.

Departing northern NZ to the north for the tropics:
Not this week. Low has formed in the Tasman Sea and is expected to travel across NZ on Tuesday to Saturday, after that the prospects are ok for good enough weather for departure from next Sunday 25 June.

New Zealand to the east (Tahiti)
A departure on Monday (depending on where you are) may be in moderate northeast winds or light winds-and may be a possibility. After Monday, the incoming low is expected to bring increasing NE winds and rain, so may as well stay-put for the next opportunity from Sunday 25 June.

French Polynesia to the west:
There is a squash zone of enhanced trade winds from now until around Wednesday 21 UTC between Rarotonga and Niue, as a large HIGH travels east along 40s.
A trough is forecast to be crossing the Austral and Society islands on Thursday UTC and then the Tuamotu Islands on Friday UTC, preceded by weakening NE winds, accompanied by showers, and followed by moderate to fresh south to southeast winds. Stay put during the trough, and jump a ride on those southerlies once the swell is ok.

If you would like more detail for your voyage, check metbob.com to see what I offer.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my website http://www.metbob.com for more information
Feedback to bob@metbob.com or txt 6427 7762212
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
Click FOLLOW at bottom right to subscribe.
To unsubscribesend a reply email saying LEAVE.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

11 June 2017

Bob Blog 11 June

WEATHERGRAM
YOTREPS
Compiled Sun 11 June 2017

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.

In this week's blog I'd like to let you in on a not so well-known trick with earth.nullschool.net, the website that gives an interactive view of data from the weather GFS mode, the oceanic OSCAR, RTGSST, and WAVEWATCHIII models and the chemical GEOS-5, and CAMS models.

When the word "earth" is clicked on, a menu appears, the first line gives the chosen timestamp for the displayed map, and the fifth line is labelled Control and allows the user to change the timestamp.

So, to go forward an hour, click the > symbol (or the k key), or to go forward a day, click the >> symbol (or do a shift k)

Also, to go back an hour, click the < symbol (or the j key), or to go back a day, click the << symbol (or do a shift j)

The "not so well-known trick" is that the model data goes forward in time for around 33 days for wind data from the GFS model. This is interesting, but keep in mind that weather is mix of pattern and chaos, and a computer model extrapolates the numbers of a captured pattern, and ignores the chaos. The normal rule of computer modelling applies, namely that its mimicry of the real-world fades to below useful after around 5 days. Still, it's interesting to watch what features may pop up next month.

Going the opposite way, into the past, is very useful indeed. I recommend that those of you who have recently finished a voyage use this feature. Looks like you will have to do it one day at a time, but from what I can see the data available goes back beyond a month. You can use this site to review the ACTUAL weather during your voyage, and zoom in and see just where wind or waves came from that ruined your sleep at such-and-such a stage of the trip. My thanks to the crew of SV LEGACY who alerted me to this trick.

The Tropics
Tropical Cyclone 04W MERBOK is forming in the China Sea and heading north, and expected to make landfall as a gale to east of Hong Kong on Monday night local.

The last week's rain map from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif shows a well-established monsoon over India and a build-up of convection around Malaysia to Philippines, also across Papua New Guinea to Solomons. This seems to be related to an MJO that is moving east. However the parameters we follow seem to show this MJO is weakening during the coming week.

The ITCZ west of Mexico also intensified last week.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
The SPCZ stretches as an almost continuous band from Papua New Guinea/Solomons to around northern Vanuatu/Wallis/Futuna and then between Southern Cooks and Society Islands. It is expected to travel somewhat to north and east this week, visiting Samoa on Thursday/Friday UTC then may go west again.

Subtropical ridge (STR)
High that is in the central Tasman Sea tonight is expected to travel to north of NZ and fade there on Tuesday.
New High is expected to form in central Tasman sea around Wednesday and then move slowly east across central NZ on Saturday UTC.

Australia to New Caledonia:
Not this week. Too much easterly wind on north side of the Tasman Highs. Also there is expected to be a trough off the Queensland coast from Monday night to Wednesday local.

Departing northern NZ to the north for the tropics:
Weather pattern is Ok for going north this week, but try and minimize time spent motoring across the light winds of the subtropical ridge.
Also avoid departing Tuesday/Wednesday due to strong winds/swell from a passing front.

New Zealand to the east (Tahiti)
On Wednesday, a deep low is expected to travel to northeast across the sea east of South Island, with Southerly storm and swell up to 11m offshore.
Wait for that to go first, may be Ok for a departure Thursday or Friday.

French Polynesia to the west:
The SPCZ is lingering as a band across the route.
IF you depart this week aiming for Niue/Tonga/Rarotonga, then will need to sail thru the SPCZ at some stage. It should be east of Niue from end of Sunday local date, and east of Palmerston from around end of Monday local date.
A voyage to Suwarrow should stay north of SPCZ in light to moderate East to NE winds.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my website www.metbob.com for more information
Feedback to bob@metbob.com or txt 6427 7762212
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
Click FOLLOW at bottom right to subscribe.
To unsubscribe, send a reply email saying LEAVE.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

04 June 2017

Bob Blog 4 June 2017

WEATHERGRAM
YOTREPS
Compiled Sun 04 June 2017

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.

Last month
Sea Surface temperature anomalies may be seen at www.ospo.noaa.gov/data/sst/anomaly/2017/anomnight.6.1.2017.gif
There continues to be more area covers by warm anomalies than by cool anomalies.
And now there is a warm river appearing along east coast of South America.

To see how the annual weather cycle and the seasons are working out, take a look at the average isobar maps for May compared with April using data from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

In May, the subtropical ridge in the southern hemisphere has travelled NORTHWARDS. This trend is subtle and doesn't show much in the isobars, but can be seen in the anomalies. There also seems to be a persistent trend for High pressure systems to linger around southern New Zealand, and this encourages southerly winds and cold fronts that herald them to often visit eastern New Zealand, a recipe for good winter alpine snow.
TRMM offers monthly rainfall maps at trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html
These show wetter than normal conditions over northern NZ. The heaviest rainfall last month was in spots from India to Papua New Guinea, also off the west coast of central America (Cyclone Adrian). Samoa had a wet month due to Cyclone Ella.

The Tropics
In my last blog, a week ago, Cyclone MORA was just forming. During the week MORA It brought a deluge to Sri Lanka and wind/rain damage to Bangladesh and Myanmar. The Sri Lanka rain marks a wet start to the 2017 Asian Monsoon, and a quick end to the 2017 Everest climbing season. More about Cyclone MORA from en.wikipedia.org/wiki/Cyclone_Mora

There are no cyclones or tropical depressions around tonight.

The last week's rain map (fromtrmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif)
shows a build-up of convection around Malaysia and Philippines, also across Papua new Guinea to Solomons /Vanuatu. This seems to be related to an MJO that is moving east, and may trigger tropical depressions in Micronesia in next few weeks.

Then again, models are picking this MJO to weaken the week.


WEATHER ZONES
SPCZ=South Pacific Convergence zone.
There is a convergence zone lingering between 5 and 10S from Tuvalu to Tokelau. Occasionally this zone affects Samoa, and Wallis/Futuna.
The main part of the SPCZ stretches from active-activity across Papua New Guinea and Solomons to quieter-activity south of Fiji and Tonga/Southern Cooks, where it merges into some jetstream cloud and the remains of an old cold front. All this is expected to travel north and east this week so that the SPCZ may reach Society islands of western FP this weekend.
Tropical accumulated rainfall for next week may be seen at windyty.com

Subtropical ridge (STR)
Next High departing Australia is likely to travel across the South Tasman Sea on Wednesday and then across Southern NZ on Thursday and Friday.

Australia to New Caledonia:
A Low is expected to form on the front in the South Tasman Sea on Monday. This Low should then travel northeast onto northern New Zealand by the weekend. This offers a period of W/SW wind son the back of this low good for getting from Australia to Noumea.
To catch these, you need to depart on Monday or Tuesday.

Departing NZ to the north for the tropics:
On Monday a small low is expected to cross the North Island. The SW winds that follow this on Tuesday offer the best opportunity for departure this week. They voyage is likely to encounter some NE winds and a passing front around Friday. If you wish to wait for the next opportunity, then that may be around middle of next week 13/14 June.

New Zealand (Northland) to the east (Tahiti)
After the Monday Low, there should be good departures to the east on Tuesday and Wednesday.

French Polynesia to the west (New):
There is an approaching SPCZ.
IF you depart this week aiming for Tonga then you will need to sail thru the SPCZ to get to Tonga, or IF you aim for Palmerston/Raro/Suwarrow, then will need to get across the light winds ahead of the approaching SPCZ.
For a voyage with good trade winds, wait for the SPCZ to fade or pass over Society Islands around Sat 10 June and then depart around 11 June.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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28 May 2017

Bob Blog 28 May 2017

WEATHERGRAM
YOTREPS
Compiled Sun 28 May 2017

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.

The tropics
There are two tropical depressions on watch tonight-one in the Bay of Bengal (linked with the arrival of the monsoon) and another in the South China sea.
The status of the tropics as summarized at ruc.noaa.gov/tracks/

There has been a build-up of convection in the equatorial Indian Ocean and this is related to an MJO that is heading east. At this time of year it should induce extra convection around the Philippines in a few weeks.

Rain for the past week is at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif
Trends in the weekly rain maps show that convection remains strong about Indian Ocean to Philippines. Activity is also increasing along the ITCZ.
In the South Pacific there is a clear path of a small low that descended from an upper trough to reach the surface near Fiji and then travel southeast across southern Tonga to Southern cooks. This system gave brief gales to southern Tonga but was NOT a tropical cyclone. See matangitonga.to/2017/05/23/gales-warning-tongatapu

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
Recent activity in the SPCZ was taken away to the SE by last week's low, and all that is left this week is near 5 to 10S, north of its normal position.
Tropical accumulated rainfall for next week can be seen at windyty.com

Subtropical ridge (STR)
High in the Tasman Sea is expected to travel east along 30S this week.
The next High is expected to spend this week over interior of Australia. This means that the nights are now long enough to cool and densify the over continental Australia encouraging the STR to shift north. This High is expected to stretch towards Southern NZ next weekend.

Australia to New Caledonia:
The GO EAST RALLY took the opportunity to sail last week and are now (mostly) in Noumea.
There is a trough crossing Brisbane over next few days so good idea to let that pass and then latch on to the Southerly winds that follow, around Wednesday, for departure.

Departing NZ to the north for the tropics:
The DOWN UNDER RALLY took the opportunity to sail north on Saturday (27th) along with lots of yachts from Opua/Marsden cove. The strong subtropical ridge is likely to ensure a slow trip; however, it should also keep nasty troughs at bay.
A trough is expected to move on to NZ by late Tuesday followed by a Low traveling NE across the country (in upper SW winds) from Thursday to Sunday, followed by strong SE winds.
So those not departing on Monday should wait until AFTER next weekend (Queens Birthday Holiday on Monday) for next good departure opportunity.

New Zealand (Northland) to the east (Tahiti)
Avoid departing on Tuesday because of a likely passing trough.
A Low is expected to take its time crossing the northern NZ region from Thu 1 to Mon 5 June. Any departure from Wed 31 May is likely to encounter too much in the way of easterly winds from that low by Saturday. SO, either go Monday or wait until next week.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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Feedback to bob@metbob.com or txt 6427 7762212
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21 May 2017

Bob Blog 21 May

WEATHERGRAM
YOTREPS
Compiled Sun 21 May 2017

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.
=================================
The state of the ENSO
In 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 standardized difference in the barometer readings between Tahiti and Darwin. When the SOI is more than plus one (standard deviation from its mean) for more than a month we call it a LA NINA event, and when it stays more than minus one we call it an EL NINO event.

El Nino and La Nina are tropical influences on the weather: the La Nina shifts the subtropical ridge away from the equator and the El Nino draws the subtropical ridge closer to the equator. This affects the seasonal weather all around the planet.

From May 2015 to May 2016 we had an extreme El Nino. Then there was a weak La Nina in October 2016, and then we had weak plus/minus events. However over the past few weeks the SOI has dived to below minus 1 (-10 in the graph scale used here). If this value is held for three more weeks then we are having a new EL NINO.
A trend toward El Nino as seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekly

In the Ocean:
The eastern equatorial Pacific Ocean acts as a heat storage area during an El Nino, or becomes cooler than normal during a La Nina. This plays with the heat budget of the atmosphere and thus with the weather patterns.
There were warm seas during the El Nino of 2015/2016 and cooler seas late last year and earlier this year. Since Feb/Mar the seas in the target area have warmed, but not yet enough to call this an El NINO (as far as the ocean is concerned).
Seas are warm but not yet an El Nino, as seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=nino34&p=monthly

The International Research Institute of the Climate Prediction Centre compile data from several ENSO prediction models. Looking at the Nino3-4 parameter, most models do NOT go for an El NINO, but they do go for higher than normal sea temperatures, with a reasonably flat trend for the next year.
CPC/IRI predictions are at
iri.columbia.edu/our-expertise/climate/forecasts/#ENSO_Forecasts

In summary: the atmosphere is starting to show some El Nino traits, but is only weakly being supported by the ocean. This means that although we may see some weather features typical of El Nino over the next month or so, there is also room for variation and other patterns to appear.

===================
The Monsoon
AT this time of year, the noon-day sun is over 20N-the thickest part of northern India. Up until now the cooler oceanic surface winds have been held off India mainland in spite of the extra heating from the overhead sun as it travelled north. One factor in this has been the jetstreams over 30N, the Himalayas. However, we have now entered that critical part of the year, where the jetstreams shift over the Himalayas.

Himalaya is the only part of planet earth that touches the stratosphere, and some call it our "third pole". Without jetstreams, Everest becomes climbable, and we are now entering the Everest climbing season (last around 7-10 days). This is such a critical event in the annual cycle of the planet (more so than a solstice or equinox) that some meteorologists like to use it as to demark the beginning of a new meteorological year. It seems that other seasonal parameters such as ENSO seem to start and end around this time of the year. Anyway, the absence of jetstreams over Himalaya is the very event that allows the cooler oceanic surface winds to finally enter India, bringing monsoonal rain. A Monsoon arrival map may be found at www.imd.gov.in/pages/monsoon_main.php and is updated almost daily. Enjoy.
========================

The tropics
It is amazing what difference one week can make, not just in politics, but also in tropical weather. Whereas last week we had cyclones in both hemispheres, this week things have quietened and there are no cyclones around (just a tropical low north of the Philippines).
There has been a build up of convection in the equatorial Indian Ocean and this is related to an MJO that is heading east (not monsoonal). At this time of year it should induce extra convection around the Philippines in a few weeks.
Rain for the past fortnight is available at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif
===============

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
AN upper trough is building cloud over Fiji tonight. This is expected is to descend into a LOW that forms over Southern Tonga on Monday and the Niue area on Tuesday/Wednesday UTC, and then moves off to the SE. and fades. Avoid. Likely to be squally near this low.

Subtropical ridge (STR)
The force is strong with the STR this week. One High over northern New Zealand on Monday is expected to travel to east of NZ along 35S. There is likely to be a squash zone of enhanced SE winds on the northern side of this High from Monday to Thursday UTC.
Next HIGH from the Australian east coast on Mon 22 May is expected to travel east over central NZ on Wednesday 24 May.
Then another HIGH is expected to travel east along 25 to 30S across northern Tasman Sea from Fri 26 to Tue 30 may.

Australia to New Caledonia:
The GO EAST RALLY is likely to depart South Port on early Tuesday:
This should work thanks to a southerly component in the wind along the way on Wednesday as a trough forms between New Caledonia and Fiji.

Departing NZ to the north for the tropics:
Good opportunity for departing NZ is expected AFTER a trough passes off to the east on Thu 25 May.

New Zealand to the east (Tahiti)
Light winds are Ok for departure on Mon22/Tue 23 May. After that things get complicated.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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Feedback to bob@metbob.com or txt 6427 7762212
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14 May 2017

Bob Blog 14 May

WEATHERGRAM
YOTREPS
Compiled Sun 14 May 2017

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.

Tropical Cyclones DONNA, ELLA and ADRIAN

Cyclone DONNA was tripped over by Mare island in the Loyalty Group and faded quickly with its clouds merging into a trough that crossed New Zealand on Friday. Looking at its track it seems that DONNA had problems when its forward edge started encountering the high ground of New Caledonia. This can still be seen at www.met.gov.fj/aifs_prods/65648.html

Cyclone ELLA is still travelling slowly west, travelling near Rotuma tonight, and expected to weaken on Monday but may still have squalls when it gets near the northern Islands of Vanuatu on Wednesday. This can be seen at www.met.gov.fj/aifs_prods/65663.html

Cyclone ADRAIN had a brief life starting Wed 10 May (UTC) when it formed in the NE Pacific. Their cyclone season usually "opens" on 15 May, and ADRIAN now holds the record as "earliest cyclone" for the NE Pacific. It dissipated on 11 May. See watchers.news/2017/05/10/tropical-storm-adrian-forms-in-ne-pacific-as-the-earliest-on-record/

The rain from cyclone ELLA in the past week is the highlight of this week's rain map, at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, especially when compared with last week (which is showing DONNA's rain). Also note that the extra convergence zone that was between Marquesas and Galapagos a fewe weeks ago has now faded away.


WEATHER ZONES
SPCZ=South Pacific Convergence zone.
TC ELLA is expected to weaken on Monday but may bring some squalls to norther Vanuatu are aby Wednesday. Apart from that, the SPCZ this week is expected to linger from Solomons to the area between Vanuatu and Fiji. Another convergence zone is likely to longer along 15S between Samoa and the area west of Southern Cooks.

Subtropical ridge (STR)
High over northern New Zealand on Monday is expected to travel to east of NZ along 35 to 40S. There is likely to be a squash zone of enhanced SE winds on the northern side of this High from Wednesday to Friday UTC between Rarotonga and Tonga.
Next HIGH from the Australian bight is expected to linger over Tasmania from Wednesday 17 to Friday 19 May, then travel NE across the Tasman Sea to reach North island around Monday 22 May, and then across the Tasman Sea next week reaching northern New Zealand by Friday 19 May.

Australia to New Caledonia:
The GO EAST RALLY is rearing to go soon.See www.downunderrally.com/about-go-east

The HIGH in the south Tasman Sea from Wednesday is likely to maintain too much SE trade winds along the route until Sat 20 May. Then there should be a weak passing trough on Sunday, but today's data is showing this is NO LONGER EXPECTED to be followed by a change to SW winds. The next possibility for a reasonable weather pattern for departure is around Thu 25 May, perhaps. Things my change and bring this forward, so keep tuned.

Departing NZ to the north for the tropics:
The current weather of opportunity is quickly closing as the next incoming trough is expected to bring NE winds onto Northland from Tuesday. Low in southern Tasman Sea is expected to deepen from Monday to Wednesday as it travels southeast then east, and then across central NZ on Thursday. AT this stage, a departure on Friday 19 or Sat 20 May is looking good.

New Zealand to the east (Tahiti)
After the Wednesday/Thursday trough we may need to wait a day or so for the southwest winds that follow that trough to ease. Then around Sat 20 May there should be an OK opportunity for departure.

Mexico to Marquesas:
Off NW Mexico, there should be a useful north to NW flow for departure for first half of this week, but then these winds may become lighter and more variable for a few days.
The ITCZ is likely to be between 9N and 3N, and light winds between 8N and 5N.
Perhaps there is better sailing if you aim for a waypoint WEST of the direct path this week near maybe EQ131W.

Panama to Galapagos
Light mostly southerly winds off Panama this week, so it's a motoring start and there are moderate SW winds between Panama and Galapagos especially from 16 to 20 May UTC (Mon to Friday local).
Convective clouds with variable winds and squalls likely from 6N to 3N.

Galapagos to Marquesas
There is still a zone of light winds about the equator near 100 to 105W, so go southwest at first. Then, when in the trades, we can go direct.
Maybe a convergence zone with squalls near 5S 100W, avoid.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my website www.metbob.com for more information
Feedback to bob@metbob.com or txt 6427 7762212
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
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09 May 2017

TC ELLA for the remainder of the week

The tropical depression we have been watching over northern Tonga for the first part of this week has now deepened into Cyclone ELLA. This is travelling west along 16S as cat1.

ELLA is expected to become category 2 (winds up to around 50 knots may gust to 75 knots) and curve to the south reaching the Lau group on Friday and over the weekend.

For latest up to date details on ELLA go to www.met.gov.fj/aifs_prods/65663.html
or if you only have email, send one to query@saildocs.com, no subject needed, with the message:
SEND http://www.met.gov.fj/aifs_prods/20036.txt
=====================================================

07 May 2017

Bob Blog 7 May 2017

WEATHERGRAM
YOTREPS

Compiled Sun 7 May 2017
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.

Tropical Cyclone DONNA
DONNA may have formed a few days "out of season". However, this should be no great surprise as the sea temperatures all around the tropical Pacific are warmer than normal and that's the trigger.
Sea Surface temperature anomalies may be seen at www.ospo.noaa.gov/data/sst/anomaly/2017/anomp.5.4.2017.gif
These warmer than normal seas are already breeding tropical depressions in the NE Pacific, and their "Cyclone Season" is meant to start on 15 May, but there is already an interesting collection of possible depressions off the Honduras west coast this week.

To see how the annual weather cycle and the seasons are working out, check out the average isobar maps for April at
www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

Back in March, the subtropical ridge was near latitudes 30 in both N and S hemispheres. Then, in April, that ridge noticeable shifted NORTHWARDS, especially over the mainlands of Australia and South America, and in the northern Hemisphere it has weakened over the mainlands of Eurasia and North America.

The anomaly map shows that that the troughy area that was over Australia in March has been replaced by a ridgey area--- it seems to have weakened and shifted to the NZ area. This is consistent with the Tasman Tempest and Cyclone Cook events that brought NZ record April rainfall.

The Last 30 days of rainfall, and its anomaly, as seen at TRMM
trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html
clearly shows that the wetter than normal conditions over NZ. This also shows Vanuatu had a wetter than normal April.

The Tropics
TC DONNA reached Cat 4 early today and is now Cat 3 and continuing to curve South then south-southeast then southeast reaching the Iles des Pins area by around 5pm local time Wednesday. By then it should have weakened to Cat 2.

Its latest official track for DONNA is available from www.met.gov.fj/aifs_prods/65661.html

A trough is crossing that Tasman Sea and moving onto New Zealand later this week. This trough should capture the remains of DONNA when it exits from the tropics on Thursday and help push them south-eastwards off to the east of NZ on Friday/Saturday. DONNA is likely to lose strength when it leaves the tropics because it will encounter a Jetstream and get decapitated. Cyclone COOK, by way of comparison, was able to get between two jetstreams and thereby deepen as it approached NZ.

There is a small tropical depression over the Tonga area tonight. It is expected to fade as it moves off to the north of Fiji over next few days.

The rain from cyclone DONNA in the past few days is the highlight of this week's rain map at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif
especially when compared with last week.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is expected to remain strong in a zone from Tonga to Southern Cooks.

Subtropical ridge (STR)
High over northern New Zealand tonight is travelling off to the east.
Next HIGH from the Australian bight is expected to travel east across Tasmania on Friday 12 May, and then across the Tasman Sea next week reaching northern New Zealand by Friday 19 May.

Australia to New Caledonia:
The GO EAST RALLY is rearing to go soon.
SEE www.downunderrally.com/about-go-east
The HIGHS crossing the Tasman Sea are producing too much of a Southeast wind on this route for a good sail to Noumea. The Low that is expected to be crossing the Tasman Sea this week (with a trough that captures the remains of DONNA) is too far south to turn the winds southerly long enough for a nice voyage to Noumea. SO, may as well stay put this week.
And during next week there is another HIGH, maintaining more SE winds along the route until at least Thu 18 May. Perhaps soon after that there should be a favourable swing of wind. More about this next week.

Departing NZ to the north for the tropics:
Trough is moving onto New Zealand from the Tasman Sea, and crossing the North Island on Thursday. Because it is preceded by increasing NE winds, may as well stay put until this trough has gone. AT this stage, a departure on Friday 12 or Sat 13 May is looking good.

New Zealand to the east (Tahiti)
After the Thursday trough we may need to wait a day or so for the southerly winds that follow that trough to ease. Then around Sat 13 or Sun 14 May there should be an OK opportunity for departure.

Mexico to Marquesas:
If a tropical depression does deepen off the Honduras coast next few days then it should go north and make landfall near the Guatemala/Mexico border by Sun 14 May, and thus not affect anyone departing from La Paz area. Keep an eye out just in case.
Off NW Mexico, there should be a useful north to NW flow for departure anytime this week, but it may fade next week.
The ITCZ is likely to be between 7N and 2N, and light winds between 7N and 2N and from 1S to 3S. Different from last week, and perhaps better sailing winds if you aim for a waypoint EAST of the direct path this week near maybe EQ 123W.

Panama to Galapagos
Southerly winds off Panama are light until Monday then expected to become moderate until wed 17 May.
SO, Sunday/Monday offer the best possible departure conditions this week.
At 7N we may be deflected to west southwest by the S/SSE winds - sadly that's into the main convective clouds with squalls.

Galapagos to Marquesas
There is still a zone of light winds about and wets of Galapagos.
To avoid these, go to 5N 93W and then can go direct.
Maybe a convergence zone with squalls near 9S 120W, perhaps.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my website www.metbob.com for more information
Feedback to bob@metbob.com or txt 6427 7762212
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
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>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

03 May 2017

TC DONNA

The tropical depression that has been lingering around to northeast of Vanuatu got its act together last might and is now a Cat 2 tropical cyclone called TC DONNA.

It is heading southwest towards Sola in northern Vanuatu where it should arrive around 5pm Thursday local and intensify of Cat 3, with winds near centre around 64 to 85 knots.

For an updated track map for TC DONNA see www.met.gov.fj/aifs_prods/65661.html

On Friday, TC DONNA is expected to maintain Cat 3 and turn south-southeast-wards. If it continues its current pace, TC DONNA at this stage, is likely to reach the Port Vila area by late Sunday. Then it may start to travel faster and weaken passing the Tanna area around Monday.

Too far away at this stage to be sure, but next week as TC DONNA leaves the tropics, one likely scenario is for it be captured by the trough which is likely then to be moving from the Tasman Sea towards NZ. This should take its remains south-eastwards towards NZ's East Cape by around Friday 12 May.

Any vessels on their way from NZ to Fiji at present should aim for a waypoint east of their direct path so that they may be in position when the winds around Fiji turn to be from the NE early next week. the trough that contains DONNA is not expected to get past 175E until after Wed 10 May

Any vessels stopping at Minerva are advised that a large HIGH is now travelling east from the Tasman Sea across NZ this weekend and then off to east of NZ early next week. This HIGH enhances the trade winds on its northern side, so there is likely to be a period of easterly winds at Minerva around 20 gust 30 knots (maybe a bit more) from end of Friday 5 May to Thursday 11 May, Then a trough on Friday 12 /Sat 13/Sun 14 May.


Bob McDavitt

30 April 2017

Bob Blog 30 April 2017

WEATHERGRAM
YOTREPS
Compiled Sun 30 April 2017

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.

The Tropics
TC FRANCES is fading in the Timor Sea.
This evening a tropical depression has formed near 10S 163E or between Solomon Islands and northern Vanuatu, called 99P by Guam. See www.met.gov.fj/aifs_prods/0991.jpg
Some global weather models deepen this system during the coming week. They still are coming up with differing possible tracks, and the most likely if to be slowly to the SE at first then the SW or WSW, maybe into the Coral sea by end of the week. If you are entering this area this week then keep an eye on 99P.

There is another depression in the Indian Ocean being watched at present, known as 98P
These systems can be seen at ruc.noaa.gov/tracks/

Rain from last week, compared with previous week, from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, shows wet areas near Palau (first in months), Darwin (from TC FRANCES) and Missouri, USA. The South Pacific convergence zone is more united, but seems to be weakening about and east of Marquesas.


WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is strong this week and contains Tropical Depression 99P which is expected to deepen and go SE at first then slowly SW or SSW across Vanuatu an into the Coral Sea. Its future remains uncertain, and it is the system to watch this week.
Forecast for Tropical accumulated rainfall may be seen at from windyty.com

Subtropical ridge (STR)
High in Tasman sea on Monday is expected to travel east across Northern NZ on Tuesday and then travel east along 30S.
Another High is expected to travel east across Bass Strait on Thursday and then across the Tasman Sea and North island by Sunday 7 May.

Australia to New Caledonia:
With the Highs travelling across the South Tasman Sea, and a tropical low likely over Vanuatu or in the Coral Sea, there are lots of East/SE winds between Australia and New Caledonia later this week. Best day of the week to set off is Monday. We may have to wait until Mid-May for the next good enough weather pattern for this voyage.

Departing NZ north for the tropics:
Trough crossing the North Island tonight is bring a southerly gale to Cook Strait with waves washing up on Wellington Roads, and undermining at least one house.
This trough is moving off to east of the North island o Monday and there is good enough weather pattern on Tuesday (passing ridge) for departure to points north. Those intending to g to New Caledonia should keep an eye on that tropical depression, but at this stage a TUESDAY departure looks OK.
Sadly. on Wednesday, Thursday, and Friday a Low is expected to come out of the Southern Ocean and travel NE along NZ east coast and then deepen to east of North Island.
A Tuesday departure should get north quick enough to miss any rough stuff, but a Wednesday or later departure is likely to encounter strong S/SSE winds and 3 to 4 m southerly swells near 30S on Sat/Sun.
The next good-looking opportunity seems to be Saturday 6 May.

New Zealand to the east (Tahiti)
On Wednesday, Thursday, and Friday a Low is expected to come out of the Southern Ocean and travel NE along NZ east coast and then deepen to east of North Island. if we depart Monday or Tuesday then we will need to divert to 25S near 175W to avoid the strong/gale Se winds and heavy swells around this low next weekend. I don't think this is the best weather venture for this route - I think a departure AFTER that trough, from Northland on Sat 6 May (or from Lyttelton on Friday 5 May) could go more direct, perhaps.

Mexico to Marquesas:
A moderate to strong Tehuantepec NE blast of wind near 95W is likely on 5 and 6 May.
Further north, it should be useful north to NW flow for departure anytime this week.
The ITCZ is likely to be between 6N and 2N, and light winds between 3N and 5S on the direct path. Perhaps more wind if you go a bit further west of the rhumb line. Maybe aim for 7N130W then direct.
I shall discontinue this voyage form my list next week unless someone asks for it to continue.

Panama to Galapagos
The forecast is for moderate southerly winds at panama except for a period of light variable winds on 3 and 4 May (best days this week to departs).
I shall discontinue this voyage form my list next week unless someone asks for it to continue.

Galapagos to Marquesas
Trade winds are expected to spread north and fill in this week so that a direct path may be as good as any for starters. However, there may be light winds near 10S from 125 to 135W and it may be an idea to sail around those (or motor thru them).

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23 April 2017

Bob Blog 23 April 2017

WEATHERGRAM
YOTREPS
Compiled Sun 23 April 2017

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.

The state of the ENSO
ENSO is currently neutral and forecast to move towards an El Nino over next few months.

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 standardized difference in the barometer readings between Tahiti and Darwin. When the SOI is more than plus one (standard deviation from its mean) for more than a month we call it a LA NINA event, and when it stays more than minus one we call it an EL NINO event.

El Nino and La Nina are tropical influences on the weather: the La Nina shifts the subtropical ridge away from the equator and the El Nino draws the subtropical ridge closer to the equator. This affects the seasonal weather all around the planet.

From May 2015 to May 2016 we had an extreme El Nino. Then there was a weak La Nina in October 2016, and since then we have had only a weak SOI.
See www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekly

The Ocean:
The eastern equatorial Pacific Ocean acts as a heat storage area during an El Nino, or becomes cooler than normal during a La Nina. This plays with the heat budget of the atmosphere and thus with the weather patterns. A good measure of the heat is the NINO 3.4 index

The diagram link given below compares the extreme El Nino of 2015/2016 with the previous extreme El Nino in 1997/1998. It also shows there was a period of cooler than normal sea over the past few months, and now things are slightly above normal, but not enough for this to be called El Nino.
Neutral territory is seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=nino34&p=monthly

The International Research Institute of the Climate Prediction Centre compiles data from several ENSO prediction model. This shows that the average of all models is for the NINO 3.4 anomaly to rise for the remainder of 2017 but no more than 1.0--- a rather weak El Nino. As usual, there is a large spread in the model data output, so low confidence.
CPC/IRI predictions are at iri.columbia.edu/our-expertise/climate/forecasts/#ENSO_Forecasts

The Tropics
On 16 April, Cyclone MAARUTHA made landfall on Myanmar with a central pressure of 996hPa. It was the first Northern Hemisphere cyclone to be named for 2017.
Another system, tropical depression CRISING, (4th tropical depression in the NW Pacific for 2017) formed over Palau on 13 April and made landfall over the Philippines, causing some fatalities and washing away buildings.
At present, there is another tropical depression near Palau and another near the south coast of Papua New Guinea. See ruc.noaa.gov/tracks/
Rain from last week, as seen at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, compared with previous week, shows the South Pacific convergence zone is weakening. The ITCZ is about the same, and the convergence zone between Tuvalu and Galapagos is slowly fading.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is weak and mainly over northern Coral Sea this week. There is still a convergence zone between Tuvalu and Galapagos and another near Southern cooks/ French Polynesia, but these zones are slowly weakening. Tropical accumulated rainfall for next week may be seen at windyty.com

Subtropical ridge (STR)
High in Tasman sea on Monday and Tuesday is expected to travel east across North Island on Wednesday and then fade to east of NZ.

Departing NZ for the tropics:
On Monday, a LOW is expected to be travelling SE off to the east of NZ, and may produce an uncomfortable easterly swell. Tuesday is a public holiday. For the remainder of the week there are likely to be a series of troughs approaching northern NZ from the Tasman sea, and that can be uncomfortable.
Next week, on 1 May, an upper trough is expected to move off to the east of NZ and that is likely to bring a good weather pattern for sailing north from NZ.

Australia to New Caledonia:
Passing surface troughs are too close together next few days, then an upper trough is expected to move off to east of eastern seaboard on Sun 30 April, and that is likely to bring a good weather pattern for sailing to New Caledonia.

Mexico to Marquesas:
A moderate to strong Tehuantepec NE blast of wind near 95W should last until end of 24 April.
Further north, it should be useful north to NW flow for departure until 2May and then lighter WNW winds.
The ITCZ is likely to be between 9 and 6N, and light winds between 3 and 1 N. Perhaps more wind if you go a bit further west of the rhumb line. Maybe aim for 9N130W then direct.

Panama to Galapagos
There are light variable winds at Panama for much of the coming week, but forecast is for moderate southerly winds from 28 April to 5May = not so good for departure.

Galapagos to Marquesas
There is now a zone of light winds on the direct path, and a convergence zone near 5s from 100 to 110W, so recommended 5S 100W to 10S 125W then direct.

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Feedback to bob@metbob.com or txt 6427 7762212
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16 April 2017

Bob Blog 16 April 2017, Happy Easter

WEATHERGRAM
YOTREPS
Compiled Sun 16 April 2017

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.

It's Easter again, time for new beginnings.

The track of Cyclone COOK
Cyclone COOK did a fair amount of damage to New Zealand, but not as much as BOLA (March 1988) or GISELLE (April 1968), maybe as much, or slightly more than Cyclone BERNIE (April 1982) or FERGUS (Dec 1996).
MetService have written a blog giving a summary of the track of Cyclone COOK at blog.metservice.com/CycloneCookSummary

It shows the track that was issued on Tuesday as cyclone COOK approached landfall, and the one issued on Friday, with the blue cone showing the spread of uncertainty. These maps show that COOK did not deepen as quickly or as much as the global models calculated, and took a track slightly, but significantly, further east. Nonetheless, it was a formidable feature, with gusts to 209 km/hr at White Island and at least 100 km/hr at Whakatane, and waves over 12 metres recoded at a Bay of Plenty wave buoy. It made landfall near Whakatane in the Bay of Plenty where the barometer bottomed out at 980hPa.

A power failure affected the data coming in from the Bay of Plenty as COOK approached, but using the "Last 48 hours" feature available to registered members at predictwind.com, we can fine-tune where COOK made landfall.

Data from White Island shows that soon after 3pm on Thursday 13 April there was a wind peak with gusts to 113kt/ 209km/hr, then at around 5:30pm the easterly winds turning northerly then counter-clockwise to southerly. We can surmise that the centre started off somewhat west of White Island on approach, and ended up somewhat east of White Island on egress.

At Hicks Bay around 6pm Thursday, wind went from easterly to northerly and gusted to over 60 knots /118 km/hr, so the centre of COOK made landfall west of Hicks Bay.

And Whakatane data shows the peak wind speed just after 6pm Thursday, with wind then turning counter-clockwise from southerly to easterly. This would be on the approach of the centre and sadly we don't have data to see if the wind continued to swing counter-clockwise (in which case landfall was west of Whakatane) or changed to clockwise (in which case landfall was east of Whakatane).

The Tropics
Tropical depression 19F has been slow-moving in the Tonga /Southern Cooks area for most of April so far and is now expected to fade away and maybe track to the west over the next few days. After that it looks as though the South Pacific cyclone season may be spent.
However action is already starting in the Northern Hemisphere, with 01B MAARUTHA in the Bay of Bengal heading for Myanmar (Burma) and a tropical depression (Two) forming near Palau that may move towards Philippines later this week.See ruc.noaa.gov/tracks/

Rain from last week, compared with previous week, at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif shows the track of cyclone COOK and MAARUTHA. South Pacific convergence zone is weakening. The ITCZ is returning to normal and the convergence zone between Tuvalu and Galapagos is still there, but now with gaps.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is weak and mainly over northern Coral Sea this week. There is still a convergence zone between Tuvalu and Galapagos and another near Southern cooks/ French Polynesia, but these zones are slowly weakening. The tropical accumulated rainfall for next week may be seen at windyty.com

Subtropical ridge (STR)
Large High well to east of NZ is intensifying and moving slowly NE, and may reach over 1030hPa on Monday and Tuesday UTC near 33S 148W. There is a squash zone of enhanced easterly winds on north side of this, with large swells. Avoid this squash zone.
Another High is expected to reach over 1030hPa in central Tasman sea from Tuesday to Sunday UTC, and then cross central NZ on Sun/Mon 23/24 April. There is likely to be a squash zone of strong SE winds in the Coral sea. Take care.

Departing NZ for the tropics:
Looks good for departure over next few days, but after Thursday 20 April not so good as there may be easterly swells over 3 metres to north of NZ.

Australia to New Caledonia: Too much easterly this week.

Mexico to Marquesas:
The next strong Tehuantepec NE blast of wind near 95W is expected around 24 to 25 April, and there is a minor one from 19 to 21 April.
Further north, it should be useful north to NW flow for departure until 19 April, and then lighter variable winds until 25 April.
There is likely to be just light winds between 15 and 12N, the NE trade winds should be useful from 12N to 10N---then light wind are likely from 10N to Equator. Perhaps more wind if you go a bit further west of the rhumb line. Maybe aim for equator 130W.
Intertropical convergence zone is spread out between 10N and 5N. And there is still another convergence zone near 5S, but that may ease over next few weeks. South of that zone there should be useful easterly trade winds for sailing to Marquesas.

Panama to Galapagos
OK northerly winds if you depart by 17 April local, otherwise just light SW winds around Panama.
Main convection is likely between 8N and 4N.

Galapagos to Marquesas
There is now a zone of light winds on the direct path, and a convergence zone between 5s and 9S, so need to go as far as 10S maybe 11S to avoid that. Maybe go to waypoints 7S 100W then 11S 135W then direct. The pattern is changing and may well be different in a week or so, so get updates.

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See my website www.metbob.com for more information
Feedback to bob@metbob.com or txt 6427 7762212
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
Weathergram with graphics is at metbob.wordpress.com,
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12 April 2017

Cyclone COOK compared with the WAHINE storm.

Cyclone COOK compared with GISELLE (The WAHINE storm/'68)
Posted on April 12, 2017

There are a few tropical cyclones who exit from the tropics quicker than they can unravel.
These may be called 'bolters' and Cyclone COOK is one of these.

Usually when a tropical cyclone departs from the warm seas of the tropics, its eye-wall collapses and the systems weakens. Also, the top of the system is often knocked off by a jetstream at around 30degrees south latitude, so usually the system is no longer a tropical system and is downgraded and referred to as ex-tropical cyclone (or extra tropical cyclone, meaning a cyclone out of the tropics).

The feature that once was Tropical Cyclone COOK has now left the tropics so has lost the word "Tropical", but is still spinning with a zone of stronger winds in a ring near its centre, so may still keep its name and be known as Cyclone COOK (for the meantime).

Cyclone COOK is expected to go through a period of deepening tonight (Wednesday night) as it approaches New Zealand. An ensemble of possible tracks and the average of these, may be seen at www.tropicaltidbits.com/storminfo/16P_gefs_latest.png
This "period of deepening" is expected to take place as Cyclone COOK travels south underneath a jetstream and encounters cooler air, the same process as with any mid-latitude depression deepening. This is expected to deepen the central pressure of Cyclone COOK from 994 to 984hPa overnight.

The team at www.tropicaltidbits.com have compared the track of Cyclone COOK with their extensive database of previous cyclones and listed the closest eight analogues. The most recent of these is BECKY in 2007.
It is interesting that the closest on the list is Cyclone GISELLE in April 1968, known as the "WAHINE Storm", which resulted in the sinking of the Inter-Island ferry MV WAHINE. However, Cyclone GISELLE encountered noticeably colder air near Cook Strait and went through a period of rapid deepening there as a mid-latitude system. In comparison, Cyclone COOK is only expected to deepen by 10hPa on Wednesday night and then its central pressure should remain steady on Thursday. Cyclone GISELLE may be the closest analogue in the database to Cyclone COOK, but with an analogue score of only 0.486 this is to be treated as a questionable analogue.

The Track of GISELLE may be seen at australiasevereweather.com/tropical_cyclones/1967_1968/jtwc/tropical_cyclone_giselle.htm

As mentioned in my previous blog, Cyclone COOK has an accompanying tropical depression located near Southern Cooks. See www.met.gov.fj/aifs_prods/0991.jpg. This accomplice is feeding in moist air and Cyclone COOK is turning this into rain. An analysis of the trajectory of the air reaching NZ with Cyclone Cook (from ready.arl.noaa.gov/HYSPLIT_traj.php) shows that it has come from just south of the Sothern Cooks, with a long path across tropically warm seas.

Cyclone BOLA in 1988 had an accomplice like this
- Cyclone BOLA was a 'lingerer', and Cyclone COOK is a 'bolter', so we can expect a different outcome this time; maybe much the same peak intensity of rain, but in different places and only for a day or less, not for three days in one place.

Be aware that the actual path taken by Cyclone COOK may easily depart from the forecast path, and a small change in track leads to large changes in likely conditions.
================================

09 April 2017

TC COOK not following TC BOLA

In my last blog I made some early comparisons between TC COOK and TC BOLA.

TC COOK has NOT looped around Vanuatu like BOLA - and now is heading for New Caledonia, a place BOLA did not visit---
so it seems to me now that TC COOK is moving faster and differently than TC BOLA did
-so it doesn't compare well with BOLA after all.

See my illustrated edition at tinyurl.com/k4uf2bt for a Track of BOLA and
see metoc.ndbc.noaa.gov/ProductFeeds-portlet/img/jtwc/products/sh1617.gif for a track of COOK.

As a Tropical cyclone with an eye-wall comes south, usually it will encounter increasing westerly winds aloft, often a jetstream. These winds blow the upper parts of the eye-wall downstream and "blow the top off" the feature, ending its tropical status and hastening its weakening.

TC Cook is expected to encounter that Jetstream on Wed--- that's also when it departs the tropics and may lose its eye-wall and its tropical status.

Just one more factor for possible comparison between COOK and BOLA may present itself:

When TC BOLA left the tropics and stalled north of NZ, it was between two jetstreams, and in a region of converging moisture. These combined to form a two-cell vertical circulation, maximising upward motion and thus rainfall. BOLA lingered for three days with this heavy rainmaker within it.

The Jetstreams around remains of BOLA (when it was just NE of NZ) are at tinyurl.com/kdbv6zc from

"A Diagnostic study of the extratropical precipitation resulting from tropical cyclone Bola."

by Mark Sinclair (NIwa) in Monthly Weather Review V 121 p 2690-2707

It is interesting to see that the jetstreams on early Friday local time briefly offer a similar setup to the remains of TC COOK. To see the jetstreams go to www.stormsurfing.com/cgi/display_alt.cgi?a=glob_250

HOWEVER, it seems that TC COOK is moving steadily south now and not likely to linger, , so even if it does carry within it a two-cell vertical circulation / heavy rain maker, this feature is unlikely to stay over any one place too long. Fingers crossed.

+++++++++++++++++++++++++++++++++++++
PS:
Today, 10 April, is the 49th anniversary of the sinking of WAHINE in 1968.

The LOW involved in that event started out as Cyclone GISELLE . It had left the tropics and was weakening as it approached New Zealand, but then encountered a cold front /cold air. The Jetstream above it brought about a new period of deepening--- Taking air away from the top of the feature faster than it can be replaced and thus lowering the central pressure in the low. This sort of double-life for a low doesn't occur often.

Bob McDavitt

Bob's Blog 9 April 2017

WEATHERGRAM
YOTREPS
Compiled Sun 09 April 2017
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.

TC COOK
There are five features of interest around Australia at present: TC ERNIE to NW of Australia, TC COOK neat Port Vila, TD14(19F) near Niue, a tropical depression near Darwin, and another tropical depression just north of the equator near Micronesia.
The latest satellite imagery (as seen on Google Earth) shows heaps of convective activity around northern Australia and extending to Vanuatu. And provisional track maps from ruc.noaa.gov/tracks/ show a possibly interesting week ahead of us.

The MJO is weak at present, so is not adding to this convection.

TC COOK is, at this stage, worthy of comparison with TC BOLA (a very wet and slow-moving cyclone off eastern NZ in early March 1988), for three possible similarities.
1) A close analysis of BOLA showed it made two loops around Vanuatu, making a slow-moving feature.
TC COOK is in a slow-moving environment when over Vanuatu so it may also do some loops.

2) BOLA's path off to the southeast was blocked by a large HIGH located to east of New Zealand, so that it was knocked slowly to south and southwest lingering near northern NZ. TC COOK may also be blocked by a HIGH and knocked southwest when it becomes extra-tropical and loses its tropical characteristics.

3) BOLA had a tropical depression accomplice to its east that went south over the Niue area as BOLA came south. This helped form converging "rivers of moist air" that hit the Gisborne hills in 1988. TC COOK has a similar accomplice, and the converging rivers of moist air, according to today's data, may be in eastern Bay of Plenty on Friday 14 April. Mind you, there is still plenty of time for this scenario to change, but its worth watching.

Rain from last week, compared with previous week, as seen at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, shows increasing intensity with the tropical lows around ERNIE, north of Darwin, about Vanuatu and from Samoa to Niue. The track of the remains of DEBBIE show up across central New Zealand. The ITCZ is slowly returning to normal and the convergence zone between Tuvalu and Galapagos is still there, but now with gaps. Equatorial America rains seem to be easing.


WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ is breaking into two this week with its southern half travelling south along e with TC COOK and TD 19F. The northern and NW parts of the convergence zone should stay near 5 to 10S and in the western Coral Sea. Not a good week to go sailing around South Pacific.

Subtropical ridge (STR)
HIGH to east of the South Island is expected to expand over 1030hPa as it travels slowly east along 40S from Monday to Wednesday. The High that is expected to slide form Aussie Bight to southeast over Tasmania by Tuesday is then expected to squeeze around southern NZ by Thursday and intensify as it travels northeast to east of New Zealand on Friday. Another High is expected to do this on Sunday/ Monday.
SO, Highs are dominating eastern NZ this week and mostly blocking Lows from the Tasman, but there is a gap to let lows thru on Friday/Saturday.

Tasman Sea/ NZ troughs.
The thundery front and low crossing New South wales tonight is expected to form a Low in Tasman Sea on Monday and this low will have to wait until Friday to cross over Southern NZ.
It may leave behind a low in the Tasman Sea that may fade there on Monday.
SO, this isn't really a good week for trans-Tasman travel.

Mexico to Marquesas:
Should be a good week to consider departure. No Tehuantepec NE blast of wind expected this week. And a moderate northerly is likely off shore most days this week.
As for waypoints: may need to throw one in to even-out possible direct downwind sailing. Useful NE trade winds to around 8N and then light winds to around 6S. ITCZ is near 10 to 5N, may be an idea to find a gap or go across this directly north to south to minimize squalls.
And there is still another convergence zone near 5S, but that may ease over next few weeks. South of that zone there should be useful easterly trade winds for sailing to Marquesas.

Panama to Galapagos
There should be some useful northerly winds for departure from Panama all this week and over Easter, then the prospect is for light winds. Main convection is likely between 6N and 3 to 2N.
May be some good tail currents and it is worth diverting to 5N 82W for these.

Galapagos to Marquesas
The currents seem to have reverted to a more normal west going set now. However, there are expected to be light winds as far as 5S and a convergence zone of squalls between 2 S and 8S worth avoiding by going south of the rhumb line. Maybe go to waypoints 5S 95W then 9S 123W then direct.
The pattern is changing and may well be different in a week or so, so get updates, maybe be able to cut corners next week.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
See my website www.metbob.com for more information
Feedback to bob@metbob.com or txt 6427 7762212
Weathergram text only (and translator) is at weathergram.blogspot.co.nz.
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