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

26 May 2019

Bob Blog 28 May 2019

WEATHERGRAM

YOTREPS

Compiled Sun 28 May 2019

 

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

The 3pm analysis from Fiji Meteorological Service today shows some convergence zone, a band of trade winds, and that Big fat High we mentioned last week is now moving off now to east of NZ.

 

There were around 20 yachts caught in North Minerva reef is last week s squash on. It’s easing now and yachts are stirring to get to Fiji (or Vanuatu). Eastely swell around the area was 3.5m 7 seconds earlier today, and is still around 2.7 m tonight, expected to ease to 2.3m on Monday.

 

The winds are expected to be from NE in the area on Mon/Tue/Wed, turning to light SW/W/NW on Thursday/Friday, so those heading for Tonga should wait for this weak passing trough until Thursday and then have a few days of tail winds.

 

Voyages to Suva or places further west may be able to take off on Monday. As for Savusavu, may be able to go on Mon or Tue, fall off to the west in the NE winds and when they finally swing easterly further north, go more direct

 

There are no cyclones at present, but there is p tropical depression off the central American west coast. The latest cyclone activity report is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is mainly from Solomons to the Samoa area this week.

There is also an active convergence zone lurking to south of Tahiti and the Society Islands.

 

Subtropical ridge (STR)

HIGH now east of NZ is expected to linger swell south of French Polynesia this week with a squash zone of enhanced trade winds on its northern side until Wednesday.

 

Australia to Noumea

From Brisbane area to New Caledonia: There are useful Southwest to south winds from Mon to Thursday.

 

NZ to tropics:

A series of troughs is expected across Tasman Sea and NZ this week.

One front is expected to visit Opua on Tuesday, and the local forecast is for northwest winds rising to 25 knots on Tuesday morning with rough sea, easing early Wednesday to southwest 15 knots. So, a Tuesday departure might have a bumpy start.

However, this may change, and, depending on tomorrow’s data, a Tuesday departure might be better than a Wednesday departure.

Next trough is likely to bring strong disturbed westerly winds to Northland from Thursday 30 until at least Queen’s Birthday Monday.

A Wednesday departure should be able to get far enough north to avoid these strong winds.

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If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

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19 May 2019

BobBlog 19 May

WEATHERGRAM

Compiled Sun 19 May 2019

 

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 is a tropical low NW of Fiji, called TD12F by Fiji and 95P by Guam, slowly drifting SE. It is expected to visit Vanua Levu on Wednesday and may either then linger as a trough somewhere near Fiji, or drift off SW towards NZ, or fade where it is. At this stage I’m not sure which option it may take.

 

Viewable at www.met.gov.fj/index.php?page=trackmap

 

It is quite active at present as seen at www.meteo.nc/nouvelle-caledonie/observations/images-satellite and there is a possibility it may be be briefly named as a Cat 1 cyclone

But it is in a moderate sheared environment  (differing winds which tend to rip it apart) and there is high shear on its south side with dry air, which means as it comes south it dies. See www.met.gov.fj/aifs_prods/20036.txt

 

If it’s remains linger to east of Fiji then we have the makings of a squash zone between Tonga and Minerva

 

A HIGH is expected to travel east along 35S from NZ eastwards from Friday 24 May to Wed 29 May. It is the combination of this High and that lingering trough which is expected to make a squash zone with strong E to SE winds and rough seas near Tonga to Minerva from Friday 24 May until maybe the middle of the following week. This squash zone is worth avoiding.

 

The squash zone may be seen at windy.com

 

There are no cyclones at present. The latest cyclone activity report is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

No cyclones around, but it interesting to see some potential off the Nicaragua coast so early in their season.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ has weakened into three different zones: one in the Coral Sea, one over Tuvalu by mid-week, and the third, with today’s depression NW of Fiji shifting to between Samoa /Niue and Tonga by mid-week.

 

HIGH is expected to travel east along 30 to 40S across Tasman Sea from Monday reaching NZ on Thursday then going further east of NZ from Friday 24 May until early/mid the following week. There is likely to be a squash zone of strong SE wind sand rough seas on the north side of this High between Tonga and Minerva next weekend. Avoid.

 

Australia/Tasman Sea / New Zealand

From Brisbane area to New Caledonia: Trade winds weakening on Thu/Fri and may be light winds/southerlies from Friday 24 to Tuesday 28 May offering a reasonable voyage.

From NZ to tropics: Departures early in the week to Tonga are likely to encounter squash zone near Minerva/Tonga due to combination of a stalled trough near Fiji and a HGH travelling to east of NZ late this week. Better to stay-put until squash-zone threat weaken.

Possibly Ok for getting to Fiji and looks good next few days for departure to New Caledonia.

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If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>> 

 

 

12 May 2019

Bob Blog 12 May

WEATHERGRAM

YOTREPS

Compiled Sun 12 May 2019

 

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.

 

We can now say that the 2018/2019 Cyclone season is nearly over.

There has been one last “cyclone” named today as ANN located west of New Caledonia and going west. It seems to have managed to make the threshold for being a tropical cyclone, in the lowest category 1, but is expected to weaken back to a tropical depression by Tuesday.

 

During the past week there has been the passage of an active phase of MJO or Madden Julian Oscillation across the South Pacific. It takes 10 to 20 days for the active part of an MJO event to travel across the Pacific (a burst of extra convection that can trigger cyclones). Since this MJO event is now expected to move off, we are likely to have a more subdued South Pacific Convergence zone over the next few weeks.

 

Another parameter that helps us watch pattern sin the tropics is Outgoing longwave radiation or OLR. When the tropical convergence zones are active their cloud blocks radiation from escaping to outer space, and OLR is low, coloured blue (for bubbly). When skies are clear radiation can escape to outer space and OLR is high, coloured orange or (mellow) yellow.

 

A constructed analogue forecast of future values of the OLR show that we are expected to have a phase of high OLR (orange values) over the next few weeks, and that means a subdued South Pacific convergence zone.

See diagram at www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/forca.shtml

 

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THE TROPICS

Latest cyclone activity is at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential as seen at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

TC ANN was named today and is expected to weaken as it moves of to the west.

No other cyclones around.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to weaken this week in the Coral Sea, and to be most active this week between Tokelau (north of Samoa) and Southern Cooks.

 

Subtropical ridge (STR)

New HIGH is expected to travel east along 30S across Tasman Sea on Mon and Tuesday and fade on Wed.

Next HIGH is expected to travel east along 30S across Tasman Sea from Thursday, crossing central NZ on Sat/Sun 18/19 May, followed by active trough on Sun/Mon 19/20 May.

 

Australia/Tasman Sea / New Zealand

Looks OK for departure from NZ to Tonga/Fiji/Noumea on Tuesday/Wednesday 14/15 May.

A Monday 13 departure may have a bumpy start in left over northerly swell.

After Wed, stay put or may encounter some NE winds.

 

Fast moving active FRONT is expected over Tasmania on Monday and NZ on Tuesday/Wednesday followed by large swells around NZ on Thu to Saturday.

 

As that front crosses the south Tasman Sea on Tuesday, there is a brief twist to southerly in the winds between Queensland and Noumea—offering possibilities of sailing to Noumea, then again a Fri/Sat departure is looking possibly better than a Tuesday/Wednesday/Thursday departure.

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If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>>

05 May 2019

Bob Blog

WEATHERGRAM

YOTREPS

Compiled Sun 05 May 2019

 

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.

 

REVIEW of APRIL

Sea Surface temperature anomalies as at end of April may be seen at www.weatherzone.com.au/climate/indicator_sst.jsp?lt=global&lc=global&c=ssta

The main pattern changes are a slight reduction in the warmth of the Coral and Tasman Sea, a shifting to south of Australia of the cool pool that was in the South Indian Ocean, and the growth of some cool water in the Humboldt current off the west of South America.

It is sad to see these maps are mostly warm, and that the cool areas seem mainly to be melt water around the Arctic or Antarctic.

 

To see how the annual weather cycle and the seasons are working out, check the average isobar maps for past 30 days and their anomaly from www.esrl.noaa.gov/psd/map/images/fnl/slp_30.fnl.html

The subtropical ridge has had a strong month around the Sothern hemisphere, and has been split into three in the northern hemisphere. The lower than normal pressures to south of Australia are interesting.

Zooming into the NZ area, and comparing monthly anomalies for end of March with end of April, shows that the main difference is the building of High pressure over Australia, and a slight weakening of high pressure east of NZ. This means there has been a switch over NZ from mostly NE winds to mostly SW winds.

 

The last 30 days of rainfall, and its anomaly are seen at trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html

This web site seems to be having problems at present and latest data is 23 April.

Some tropical cyclone tracks in the Indian Ocean stand out. The ITCZ has been wetter than normal across Micronesia, and below normal near Galapagos. There is a “mirror Convergence Zone” along 5degrees south in the Eastern Pacific. There are dry patches appearing in the South Pacific.

 

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THE TROPICS

TC FANI has finally weakened after devasting parts of the NE coast of India.

The active phase of MJO is travelling into the western pacific this week.

There are no tropical cyclones around tonight, but there are potential areas for development mainly around north Coral sea and Micronesia. The GFS model currently is running away with the idea of a Tropical cyclone forming in the Coral sea by mid-week and maybe developing and curving counter-clockwise around New Caledonia this weekend. The EC model has a low, but it is weaker and later. Each new GFS run over the past few days has been delaying things, and that is a sign that it doesn’t have a good grasp. The models disagree a lot at this stage, and there is uncertainty until their scenarios get closer.

TC in the tropics at present, with latest cyclone activity may be seen at tropic.ssec.wisc.edu and TCFP tropical Cyclone Formation Potential at www.ssd.noaa.gov/PS/TROP/TCFP/index.html

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is expected to intensify in the Coral sea this week, and spread south. The models agree that a tropical Low forms by around mid-week, but disagree as to if/when it deepens and how fast it travels south. Should be a branch of SPCZ from Samoa to Southern Cooks.

 

Subtropical ridge (STR)

HIGH over 1030hPa traveling around south of South Island tonight is expected to then go NE along 45 to 40S east of NZ. This high should block the troughs in the Tasman Sea until this weekend.

 

Tasman Sea troughs

Low is travelling south into the South Tasman sea on Monday and fading by Wednesday.

Next Low is expected across Bass Strait by Thursday and then across NZ by Sunday 12 May=Mother’s Day.

 

Australia to New Caledonia.

If the GFS model is correct, then a low from the tropics may curve around New Caledonia 11/12 May. That’s no good. Stay put and hope for something better next week.

 

NZ to Fiji/Tonga

With such a dominant High to east of NZ there is a possible departure on Monday, but after that there is too much NE wind between NZ and the tropics until that trough crosses NZ on Mother’s Day. There maybe a good enough departure next week, but unsure at this stage.

 

Panama to Marquesas

Light variable winds in the Gulf of Panama for a motoring start. Then mainly SW winds between 5N and Galapagos area so some tacking may be required for that. Trade winds from the SE are likely for west of around 100W so that’s when to turn to Marquesas.

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If you would like more detail for your voyage, then check metbob.com to see what I offer.

Or Facebook at /www.facebook.com/metbobnz/

Weathergram with graphics is at metbob.wordpress.com (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>>

 

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