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

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.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

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