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

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.
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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.
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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.
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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,
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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