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

25 August 2019

Bob Blog 25 Aug

WEATHERGRAM

YOTREPS

 

Compiled Sun 25 August 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.

 

PUMICE

There was an eruption of a undersea volcano at 18.325S 174.365W or around 27nm NW of Vava’u early in August that has ejected a raft of pumice that drifted SW to be around 60nm west of Late island off west coast of Vava’u, affecting voyages from Vava’u to Fiji.

It seems to currently be drifting north slowly. and dispersing.

A write-up on this pumice is at earthobservatory.nasa.gov/images/145490/a-raft-of-rock

and an excellent sailor report about this pumice appeared on facebook on 15 Aug at tinyurl.com/yxgfutte

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SUDDEN STRATOSPHRERIC WARMING

Your may have heard that a “Sudden stratospheric warming (SSW) is occurring over the Antarctic south of Africa to Australia, and wondered what that means. It may buckle the Polar vortex so that some cold streamers from the Southern Ocean may travel onto Australia/NZ in September.

This has only been recorded in the Southern hemisphere twice before (Sep 2002 and Sep 2010) and both times saw temperatures in New Zealand plunge.

In the Southern Hemisphere during winter, a ring of stormy and freezing weather encircles Antarctica, spinning clockwise. This is called the Polar Vortex and extends into the stratosphere, 30 to 50km high, and it is usually very good at locking the cold close to the Pole.

 

Stratospheric winds at 70hPa (near 18km) on 27 Aug may be seen at earth.nullschool.net showing zone of calm distorting the Polar Vortex.

 

Sometimes the winds in the stratosphere temporarily weaken, or even reverse, leading to a zone of sinking air, which warms the stratosphere as it compresses downwards, and this is called a SSW. It may cause the Polar Vortex to buckle, which then filters down towards the surface and send out streams of Antarctic chilled air northwards. In this case the most likely time is early September into Australian bight, , but there may be ramifications throughout September for the Tasman Sea. .

 

Stratospheric warming mid-last week may be seen at www.newshub.co.nz/home/new-zealand/2019/08/weather-niwa-warns-rare-sudden-stratospheric-warming-to-blast-nz-with-icy-streamers.html

 

THE TROPICS

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

There are three active tropical cyclones., DORIAN heading for the Caribbean , IVO staying offshore of west coast of Mexico and BAILU fading on the coast of China.

There are several areas for potential development, especially around NW Pacific and in he North Atlantic--- as expected at this time of the year.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stretch from south of the Solomon Islands across northern Vanuatu to Tuvalu, and may visit north of Fiji early in the week.

Passing trough over Palmerston/Aitutaki on local Sunday (tomorrow) , and bora Bora on local Monday/Tuesday with mainly light winds.

Passing trough over Niue on local Tuesday, to Palmerston/Aitutaki local Wednesday, and Bora Bora/Papeete on local Friday/Saturday, with a swing to NE then SE winds.

 

Subtropical ridge (STR)

After several weeks, the STR is finally shifting south onto NZ. remains north of NZ this week, High is expected to travel east along 35S across Tasman sea on local Tuesday and northern NZ on Wednesday, then fades off to the NE.

Another HIGH is expected to travel east along 45S across the Tasman Sea on Thursday and Friday and then across NZ on Sat/Sun.

 

Tasman Sea /NZ/Aus

SW flow easing on Monday/Tuesday. Between the Highs, a trough is expected to cross NZ on Thursday and fade over the North island on Friday.

A low is expected to form off Sydney on Thursday and travel to the NE then E and may reach norther NZ(GFS model) or Southern NZ (EC model) by  mid-next-week.

OK to head for NZ so long as you can reach it before possible strong winds early next week.

From Noumea to Aus may encounter a passing trough followed by a period of up to strong southerly winds south of Brisbane .

 

Tahiti to Tonga

The burst of large SW swells that affects this route south of 20S today/tomorrow should ease by late Monday local time.

Voyage departing this week may encounter a passing trough, but this isn’t expected to be big deal.

 

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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

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

18 August 2019

Bob Blog 18 Aug

WEATHERGRAM

YOTREPS

Compiled Sun 18 August 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.

 

SAM

We have had a taste of wintery weather in New Zeland during past two weeks, A good parameter to watch, to forecast these blasts is the Southern Annular Mode (SAM), or its proxy called the Antarctic Oscillation (AAO),

SAM describes the north to south movement of the westerly wind belt that circles Antarctica, so it can be used as a predictor for cold air reaching our mid-latitudes.

 

When SAM is positive, the belt of strong westerly winds contracts towards Antarctica. This results in weaker than normal westerly winds and higher pressures over mid latitudes, limiting the northern extent of cold fronts.

 

A negative SAM event indicates an expansion of the belt of strong westerly winds into the mid-latitudes. This weather pattern results in low pressure systems over mid-latitudes such as New Zealand, with more (and stronger) storms.

 

We can see the latest forecasts for the AAO (a good proxy for SAM) at

www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/new.aao_index_ensm.html

This shows a gradual rise from negative mode towards maybe something more positive, but there is a large amount of variation in the ensemble.  We are still in the grips of winter.

 

THE TROPICS

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

There are currently no tropical cyclones. LEKIMA made landfalls in southeast Zhejianng province  (Cat 2) followed by KROSA hitting mainly southwest japan and killing three.

Activity in the SE Asia area is expected to continue during the next week or two due to a Madden-Julian Oscillation event transiting the region.

 

WEATHER ZONES

 SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stretch from  Solomon Islands across northern Vanuatu  to northern Fiji, with another CZ hovering from Tokelau to Suwarrow as a passing trough.

Passing trough over Niue on local Sunday, to Palmerston/Aitutaki / Suwarrow local Monday, and Papeete on local Monday to Wednesday, with a swing to  NE then  SE winds.

 

Subtropical ridge (STR)

The STR remains north of NZ this week, but a new High is expected to spread into the Tasman Sea near 30S from Wednesday, passing across the north of NZ on the weekend. This may be followed by another High across the Tasman early next week.

 

Tasman Sea /NZ/Aus

Trough is expected to visit NZ on local Tuesday, followed by strong west to SW winds in the Tasman until Friday, with SW 4m swells reaching as far north as Fiji by Saturday.  Peak swell in western Tasman late Thursday over 8m. Trans-Tasman and NZ to tropics voyages this week should wait out those swells.

Tahiti to Tonga: Looks good to go this week with rather weak winds. May want to go north of rhumb line to avoid light winds, and larger swells.

 

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

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).

This  email has come from Weathergram archive (with translator) at weathergram.blogspot.co.nz.

Contact is bob@metbob.com or txt 6427 7762212

>>>>>>>>>>>>>>>>>>>>>>> 

11 August 2019

Bob Blog 11 Aug

WEATHERGRAM

YOTREPS

Compiled Sun 11 August 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 state of the ENSO = neutral

 

The Atmosphere:

El Nino and La Nina are opposite ends of the swing of an identifiable tropical influence on our seasonal weather: the La Nina, caused by cooler than normal seas along the equatorial eastern pacific. shifts the subtropical ridge away from the equator, and the El Nino, with warmer than normal seas, draws the subtropical ridge closer to the equator. Their comings and goings can last several months, maybe over a year, and so their status can be used to help forecast the weather for the coming season.

 

ENSO = El Nino/Southern Oscillation. The main parameter we watch from the atmosphere is the Southern Oscillation Index SOI (30 day running mean) as it sums up the whole weather pattern over the South Pacific in one number. It is based on the standardized difference in the barometer readings between Tahiti and Darwin, in other words it counts the average number of isobars between them on the weather map. 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.

 

Since March 2019 the SOI has been mostly negative, and in past few weeks it has been on the verge of an El Nino, but now it is relaxing.

As seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=soi&p=weekly

(Note that in this graph on the vertical axis 10= 1 standard deviation)

 

The Ocean:

NINO3.4 is a region in the eastern equatorial Pacific Ocean that 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.

 

At the farmonline web site we can see that NINI3.4 has been warmer than normal for the past year , and verging on El Nino values in last October and March, but recently has been mostly trending downwards. Atmosphere and Ocean are getting back in phase,

Moving away from El Nino as seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=nino34&p=monthly

 

The warm waters in the NINO3.4 area are just near the surface, and a temperature/depth graph shows cooler waters below. This speaks against any swing to El Nino in the near future.

 

Below sea level temperatures and anomalies may be seen at www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_update/wkxzteq.shtml

 

The International Research Institute of the Climate Prediction Centre compiles data from several ENSO prediction models. The model predictions for the Nino 3.4 SST anomaly is that the seas ae likely to stay as they are for the rest of this year. But three models are predicting a swing to the cool side.

See CPC/IRI dated 19 July from iri.columbia.edu/our-expertise/climate/forecasts/enso/current/

 

Latest SST anomaly map shows swirls of cool blue water over the eastern Equatorial Pacific. The Northern Hemisphere is mostly above normal. In the Sothern hemisphere there are areas of cool water around Indonesia, Western Australia and Aussie Bight (Positive Indian dipole), the Eastern Pacific Ocean, and the Southern Ocean. From Fiji to east of NZ New Zealand, seas are continuing warmer than normal. However, Tasman Sea is returning to normal.

See Sea surface temperatures across the Pacific on 8 August from www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html

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THE TROPICS

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

 

It’s been a busy week in the Western Pacific with LEKIMA making landfall in China and now KROSA seemingly heading for Japan.

There are areas of potential development west of central America and near the Equatorial Eastern Atlantic.

 

Activity in the SE Asia area is expected to increase during the next week or two due to a Madden-Julian Oscillation event transiting the region.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stay over Solomons and travel north of Samoa into the Tuvalu/Tokelau area.

Passing trough over New Caledonia today going southeast, expected to reach Minerva on local Monday night/Tuesday.

 

Subtropical ridge (STR)

The STR remains north of NZ this week, but a new High is expected to spread into the Tasman Sea near 30S from Wednesday, passing across the north of NZ on the weekend.

 

Tasman Sea /NZ/Aus

Disturbed westerlies for eastern Tasman/northern NZ until Wednesday. Should be able to depart for Tonga on Thursday or for Noumea by Saturday, but it is a no-go week again for NZ to Australia.

 

Looks Ok for Australia to New Caledonia with a Monday departure (going east at first and then motoring a lot), and for a Noumea to South Port departure from Wednesday.

 

Tahiti to Tonga: Looks good to go this week with trade winds.

 

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

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

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

04 August 2019

Bob Blog 4 Aug 2019

WEATHERGRAM

YOTREPS

Compiled Sun 04 August 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.

 

JUNE REVIEW

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

The main pattern changes are the ribbon of cooler than normal sea around the Galapagos. There is also a return to near normal in the Tasman Sea and a return to near normal off western Australia (an easing of the Positive Indian Dipole

To see how the annual weather cycle and the seasons are working out, we can check the average isobar maps for past 30 days and their anomaly from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

The subtropical ridge is much the same as last month. The monsoonal trough has deepened and shifted north over Asia.

Zooming into the NZ area, and comparing monthly anomalies for end of last month with now, shows that the subtropical ridge STR is slightly north of where it was last month. The anomalous trough over NZ is closer to the mainland than last month,

 

THE TROPICS

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

It’s been a busy week in the Pacific and still is with ERICK, FLOSSIE and now GIL travelling west towards Hawaii. Also FRANCISCO near Japan.

There are areas of potential development in the China Sea, near Bangla Desh, and now also in the Atlantic. The Cyclone Season is heating up.

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ stay over Solomons and stretch across norther Vanuatu o the Fiji /Samoa area.

Passing trough over the Gambier Islands on local Sunday/Monday 1014hPa.

 

Subtropical ridge (STR)

SAM went negative last week as expected allowing the cool air of the Southern Ocean to spread into the Tasman Sea/ NZ area with big swells. As a precursor for this the STR went north of NZ. The next High is now in the Tasman Sea and is expected to travel NE on Monday and then along 25 to 30s, being NE of NZ on Wednesday.

 

A weaker ridge is expected to travel across south Tasman on Thu and the South Island (only) on Friday.

 

Tasman Sea /NZ/Aus

Disturbed westerlies for western NZ pretty much for the whole week, but easing winds on Tuesday/Wednesday offer an opportunity for v

Looks Ok for Noumea to South Port early this week, but not Ok after around Thursday.

 

Tahiti to Tonga :Looks good to go this week with trade winds.

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

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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