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

29 August 2020

Bob Blog

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.

Compiled Sun 30 Aug 2020

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The climate start to SPRING in  the Southern Hemisphere is 1 September, but I like to wait until the equinox on Sep 22 (this year).

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The Tropics

The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html

The latest death toll due to LAURA in Louisiana and Texas is 16 (many from Carbon Monoxide). At present there are two cyclones , ISELLE, west of Mexico, and MYSAk which seems to be heading for Korea. There are several areas of high potential for formation, especially in the Atlantic.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is moderate and in its normal position from PNG to Vanuatu/Tuvalu and, occasionally, Samoa.

Passing trough over Tonga on Wednesday (local) reaching Southern Cooks on (local) Friday, associated with a Low further south..

 

Subtropical ridge (STR)

RIDGE 1020hPa near 30S in north Tasman Sea, fading on Monday/Tuesday.

New High 1024hPa in Tasman Sea on Tues , travels along 35S crossing northern NZ on Fri/Sat.

 

Tasman troughs

Vigorous westerly winds south of 40S, then trough followed by cold southerly flow reaching South Island by Tuesday and north of North island on Wednesday.

Next trough over New South Wales by Friday, increasing the westerly flow over the south Tasman again.

 

From Panama: ITCZ 5N to 10N, SW winds in Panama, winds W/SW from 7N 80W to 90W.

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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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23 August 2020

Bob Blog 23 Aug

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.

Compiled Sun 23 Aug 2020

 

Weather and climate drivers.

Seasonal and climate forecasting is more complicated than normal weather forecasting. The scope of the operation is wider and involves more variables. For Climate, one consideration is the amount of incoming energy (from the sun) and how this is distributed. As earth absorbs energy from the sun, it eventually emits an equal amount of energy to space Eventually. The (temporary) difference between incoming and outgoing can be measured and is given the name Radiative Forcing (RF). Volcanic dust is an example of one of the climate variables. Human-caused climate drivers, such as the amount of heat-trapping gases like CO2 and methane and the change in land-use have a trend, but at this stage, are not taken into account by seasonal forecasters. Seasonal forecasts use several regional based parameters to help decide what may happen in the next few months. ENSO, IPO, STR, SAM and MJO are the main parameters.

A comic way of reviewing and enjoying the effect of these on SE Australia is given at www.dpi.nsw.gov.au/climate-and-emergencies/seasonal-conditions/climatedogs

 

ENSO:

The El Niño–Southern Oscillation (ENSO) is currently neutral. However, in the OCEAN continued cooling of the tropical Pacific Ocean, changes in tropical weather patterns, and climate model outlooks shifting further towards La Niña, means that ENSO’s Outlook has moved to a La Niña ALERT.

The chance of La Niña forming in 2020 is around 70%— roughly three times the average likelihood. In the atmosphere, trade winds are stronger than average, while the Southern Oscillation Index (SOI) remains neutral but positive (indicating a La Nina trend). All international climate models surveyed suggest the tropical Pacific Ocean will cool further, with three of the eight models reaching La Niña thresholds in September, and two more in October.

For New Zealand this is likely to first bring the sub-tropical Ridge southwards with dry spells during the Spring, but it may encourage NE winds and wet spells in Northland during summer.

 

IPO:

The Indian Ocean Dipole (IOD) is currently neutral, despite the index dropping sharply recently. Large parts of the Indian Ocean are warmer than average, with some weak cool anomalies near the Horn of Africa. Half the six surveyed models indicate negative IOD thresholds could be met or exceeded during spring. This may increase the chance of rain in Australia but has little impact upon New Zealand.

 

SAM

The Southern Annular Mode (SAM) is currently negative and is expected to soon become weakly positive. A negative SM encourages southerly outbreaks.

 

MJO

The Madden–Julian Oscillation (MJO) is in the eastern Pacific and is expected to strengthen as it tracks eastwards towards Africa. At this time of year an MJO pulse in this region has little influence over NZ.

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The Tropics

The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html

There are two active storms in the Gulf of Mexico MARCO and LAURA and both seem to be heading to Louisiana, MRCO on local Sun/Mon then Laura on locl Tues/Wed Also BAVI is likely to make landfall over Korea. There are several areas of high potential for formation., especially west of central America.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is moderate and has shifted to north of normal near 10S from 150E to 160W.

Passing troughs over New Caledonia on Monday and over southern Tonga on Local Tuesday/ to Thursday.

 

Subtropical ridge (STR)

HIGH 1024hPa should get into Tasman sea at 30S n Thu and travel along 30S past northern NZ on Sunday over NZ at present is expected to travel east along 35S and build to 1040hP near 150W by mid-week, with a squash zone of enhanced trade winds along 25S with swells up to 4m from 145W to 155W.

 

Tasman troughs

Low off NSW likely to deepen to 988hPa over South Island on Mon wit a trough ove r North Island, then Low likely to go southeast and deepen to 980hPa. Low is followed by a vigorous West to SW flow over Tasman/NZ for remainder of the week with embedded weak troughs.

 

From Panama: ITCZ 5N to 10N, SW winds in Panama.W/SW winds from 7N 80W to 98W.

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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

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

15 August 2020

Bob Blog 16 Aug

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.

Compiled Sun 16 Aug 2020

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The Tropics

The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html

There are two active storms in the Atlantic now staying offshore, and a tropical depression in the North Pacific at present, and there are several areas of high potential for formation., especially west of central America.

 

SPCZ=South Pacific Convergence zone.

SPCZ is weak and mainly over Solomon island to Vanuatu this week, but there is o a convergence zone over Tuvalu and Tokelau /Samoa extending along 10S to near Northern Cooks.

Passing trough over New Cal on Monday, Fiji local Tuesday, Tonga local then it goes to southeast. 

 

Subtropical ridge (STR)

HIGH 1030hPa over NZ at present is expected to travel east along 35S and build to 1040hP near 150W by mid-week, with a squash zone of enhanced trade winds along 25S with swells up to 4m from 145W to 155W.

 

Tasman troughs

Low 998hPa east of Bass Strait tonight goes south of NZ on Wed. Associated front crosses NZ on Wed, preceded by strong NE winds Tue, and is expected on Thu to develop a Low below 999hPa off east coast of NI that goes South. Another Low 986 hPa expected in Tasman Sea around d 45S on Thurs passing south of NZ on Friday. These lows give Tasman/NZ a westerly flow from Wed to the weekend.

 

From Panama: ITCZ 10N to 7N, NW winds in Panama for starters until Tues then SW winds, W/SW winds from 7N 80W to 94W.

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

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

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

09 August 2020

Bob Blog 9 Aug

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.

Compiled Sun 9 Aug 2020

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State of the ENSO

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. 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.

 

The Atmosphere:

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 a brief El Nino late in 2019 the ENSO has been roller-coasting between weak positive and negative values. For the last three weeks it has been positive (a La Nina trend). The sub-tropical ridge has recently been (on the average) rather static,

 

The Ocean:

The sea surface temperatures in the equatorial eastern Pacific were warmish early this year but has been showing a cooling (La Nina) trend since May.

 

Sea temperature anomaly map shows a spreading of cooler than normal seas.

The cool Humboldt current has extended to the Galapagos.

Also

Waters just beneath the surface are slightly cooler than normal. These trends are towards a La Nina.

The International Research Institute of the Climate Prediction Centre compiles data from several ENSO prediction models.

The AVERAGED model forecast is going for a weak La Nina during Sep Oct Nov (with a 55% chance) and it may linger to early next year

 CPC/IRI predictions from iri.columbia.edu/our-expertise/climate/forecasts/enso/current/

So, it looks that a weak LA NINA is coming soon

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The Tropics

The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html

There are no active storms at present, but several areas of high potential for formation., especially west of central America.

 WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is likely to shift a little north this week and be from Solomons to northern Vanuatu to Tuvalu touching Samoa at times.

Passing trough over New Cal on Monday and S Tonga /Minerva on Tue/Wed and another over S Tonga /Minerva on Friday developing into a Low near Niue on Sat (local Friday).

 

Subtropical ridge (STR)

HIGH 1020hPa north of NZ travelling east along 30S on Mon/Tues.

Next High 1020hPa East of NSW on Tues gets to South Island by Thu then is expected to intensify to 1034hPa off eastern NZ by Sun/Mon.

 

Tasman troughs:Low 1008hPa east of Sydney tonight is expected to travel east to Northern NZ on Tue/Wed dropping below1000 hPa, followed by strong southerly over NZ on Wed.

Another low 1008 is expected to form east of NSW by Sat 15 Aug.

 

From Panama: ITCZ 10N to 5N, NW winds in Panama for starters until Wed, but W/SW winds from 7N 80W to 90W.

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

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

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

 

 

02 August 2020

Bob Blog 2 Aug

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.

Compiled Sun 2 Aug 2020

REVIEW OF THE LAST MONTH (July 2020)

Sea Surface temperature anomalies can be seen at https://www.weatherzone.com.au/climate/indicator_sst.jsp?lt=global&lc=global&c=ssta

Not much change since in the sea surface temperatures during July. But there is still a slight weakening in the warm pool in the Indian Ocean/Tasman Sea/Fiji. However, the possibility of a NEGATIVE Indian Ocean Dipole - bringing above-average rainfall over parts of Southern Australia later this year - has weakened.

ENSO is currently neutral, but, according to BoM (Australia) that cooling sea in eastern equatorial Pacific is significant. ENSO (El Nino/southern Oscillation) is likely (around 50%) to bring a La Nina later this year. La Nina tends to bring the subtropical ridge southwards.

SAM (Southern Annular Mode) is currently positive for a few weeks, but had 3 dives to the negative in July encouraging southerly outbreaks and is likely to go negative next week.

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

  Pressure anomolies for past few weeks (below)

The Atlantic high has increased in intensity (as per normal for July). The monsoon has also increased in intensity.

Zooming into the NZ area, and comparing monthly anomalies from last month with now, shows that the sub-tropical ridge has shifted north over NZ (as per a normal July), but strangely has intensified over Australia.

The 1010 line has shifted north a little in the Tasman Sea, allowing more fronts to spread north over NZ. A 1025hPa line has formed in southern Australia.

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The Tropics

The latest cyclone activity report is at tropic.ssec.wisc.edu and Tropical Cyclone Potential is from www.ssd.noaa.gov/PS/TROP/TCFP/index.html

There are FOUR active storms at present, ISAIAS is about to attack Florida an d there is another cyclone in Eastern Atlantic, Also SINLAKU and HAGUPIT in Asia. There are several areas around with increased potential for cyclone development.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

SPCZ is likely to be more widespread this week from Solomons to Tuvalu /Tokelau/, and should be most active over Fiji and Tonga/Niue. . Passing trough over Fiji tonight and Tonga on local Monday/ Tuesday, and Niue Sothern Cooks on local Wed/Thu. Another passing trough over Austral Islands tonight.

 

Subtropical ridge (STR)

HIGH 1036hPa well east of South Island at 33s160W with a ridge lingering over central NZ until Wed.

Next High 1020-1018hpa is expected to arrive in central Tasman Sea from Thu and travel past northern NZ on Sat/Sun.

 

Tasman Sea.

Low over northern NZ tonight moving off to east on Monday.

Another Low expected to form off Tasmania on Tues and go S of NZ on Thu/Fri to 986hpa, preceded by strong NW, accompanied by a front on Fri, and followed by strong SW flow until Sunday.

 

From Panama: ITCZ 5N to 12N, light winds maybe NW for starters this week, but W/SW from 7S 80W to 90W.

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

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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