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

28 October 2018

Bobblog 28 Oct

WEATHERGRAM

YOTREPS

Compiled Sun 28 Oct 2018

 

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 = trending towards an El Nino

The Ocean:

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.

Latest SST anomaly map shows warmer yellow/orange waters appearing around the Easter Equatorial Ocean between the Galapagos and the dateline.  See Sea surface temperatures across the Pacific on 25 Oct from www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html

 

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 the trend in the sea surface temperature in the NINO3.4 area. The diagram shows the weekly temperature anomalies since Jan 2015, with the El Nino of 2015 looking like a hump on a camel. Since then there has been a cool period late 2016/early2017, then a warm period until July 2017, and then a cool period until last June . The current warm period is intensifying and may soon reach the El Nino threshold.

Trend to an El Nino is seen at www.farmonlineweather.com.au/climate/indicator_enso.jsp?c=nino34&p=monthly

 

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 last May the SOI has been mostly negative, consistent with a weak but rather persistent El Nino. In early October it reached -1 for a week, but it needs to meet or exceed -1 for a month to meet the El Nino threshold. The blocked high that affected New Zealand over the past few weeks has been one of the factors that has relaxed the SOI, but this is about to be replaced by passing troughs, and that should help the SOI to become more negative.

SOI trend is 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 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 are likely to be near the +1.0C anomaly satisfying the definition of an El Nino during the next six months.

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

 

THE TROPICS

Latest cyclone activity are seen at tropic.ssec.wisc.edu

Super Typhoon YUTU ripped thru the Northern Mariana Islands during the past week.

And OSCAR may be going westwards for now but is expected to remain offshore.

 

Looking at the weekly rain maps, last week’s shows a relaxing of convection around Mexico and just north of Fiji, but an increase in activity about Papua New Guinea to the Mariana Islands (where YUTU formed). Not much change elsewhere.

See: trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is sitting over northern Coral sea and northern parts of Vanuatu across Wallis and Futuna to northern Tonga, and part of it may travel southeast to Southern Cooks this week.

 

Subtropical ridge (STR)

The remains of last week’s BFH are travelling eastwards along 30S well to east of NZ.

Next High is expected to form in the Tasman Sea near 30S by Tuesday and fade by Thursday as another forms near 40S. This other High is then expected to travel NE to 25S and to north of NZ over the weekend.

 

Tropics to New Zealand

Troughs are expected to cross northern NZ on Mon29/Tue 30 / Wed 31 Oct and then sun 4 Nov and then Wed 7 Nov and maybe Sunday 11 Nov. Arrange to arrive in-between troughs.

 

Between Tropics and Australia.

For those headed to Queensland or Coffs with the Down Under Go West Rally, now in its last week: Highs in the central Tasman Sea should maintain and useful easterly flow from New Caledonia to Australia this week. Winds may get over 20 knots this Thursday and again Wed 7 November.

For more info about the Go West Rally www.downunderrally.com/about-go-west

 

From Tahiti to Tonga

There is a passing trough over Tonga on Monday UTC reaching Austral Islands by Wed UTC then moving off to the south. Should be a useful SE flow after this passing trough.

 

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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

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

 

21 October 2018

Bob Blog 21 Oct

WEATHERGRAM

YOTREPS

Compiled Sun 21 Oct 2018

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.

 

There has been a Big Fat High (BFH) parked over northern NZ since 13 Oct as seen on the Auckland Airport barograph (using windy.com)

We can see how the intensifying high squeezes to isobars on its periphery closer together.  This makes a squash zone of enhanced winds, in this case from Tonga to Fiji and almost to Vanuatu.

Windy.com can also plot the past 20 days of reports.  The bottom trace is a barograph and shows that this BFH relaxed between 17 and 19 October—This also caused a temporary easing of the squash zone, and several yachts picked this window of opportunity to depart Fiji/Tonga for NZ.  They still encountered a (weakened) squash zone, and it wasn’t comfortable, but could have been worse, and they got the rare opportunity of sailing from Fiji or Tonga to New Zealand without encountering a passing trough.  Sweet, and no longer on the menu.

The squash zone is expected to relax again from Tuesday.

 

The illustrated edition shows bumps twice a day in the Auckland barograph--- these are the impact of the semi-diurnal atmospheric tide.  It is always best to log your barometer reading around 10am or 10pm (local) when it’s at the top of this cycle.

 

A quick look at the mid-atmosphere 500 hPa map around the southern hemisphere shows how the blocked high around NZ is linked to two other highs around the hemisphere. This is called the wave 3 pattern.

So, when the winds aloft decrease to a crawl because of gaps in the jetstreams, that is when the surface Highs just stay where they are and are called “blocked”. 

 

 

THE TROPICS

Latest cyclone activity is seen at tropic.ssec.wisc.edu

WILLA is aiming to make landfall near SW tip of Mexico, VICENTE is expected to weaken as it travels northwest along the coast.

 Looking at the weekly rain maps, last week’s shows a build-up of convection around Mexico and just north of Fiji, but decreasing convection elsewhere, especially around the Indian Ocean. 

 See: trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is sitting over northern Coral sea and northern parts of Vanuatu across northern Fiji and northern Tonga towards Niue and may spread towards Southern Cooks by the end of this week.

A tropical low may forms on the SPCZ to south of Niue late this week and then travel off to the southeast. Watch our for this if travelling from Tahiti to Tonga. 

 

Subtropical ridge (STR)

The BFH which has been blocked over northern NZ is expected to start relaxing by Tuesday and then to move off to east of NZ.

Next HIGH is expected to form in South Tasman Sea from Thursday and to move onto NZ early to mid-next-week.

 

Tropics to New Zealand

The squash zone between Fiji/Tonga and NZ is expected weaken by Tuesday 

A Low is expected to form between New Caledonia and New Zealand late this week and then travel east, providing the challenge of a period of southerly winds to yachts sailing south.  Yachts from Tonga can anchor in Minerva reef and wait this out.  Yachts from Fiji will need some waypoints to handle those southerly winds.

 

Between Tropics and Australia.

For those headed to Queensland or Coffs with the Down Under Go West Rally

An active trough may reach Bundaberg area from around Sat/Sun 27/28 Oct,

so that a departure from New Caledonia by local Tue 23 may encounter that trough near the Bundaberg coast where it may be active /squally. And a departure on local Wednesday may encounter that trough further offshore where it may be weaker. This timing can change.

For more info about the Go West Rally go to www.downunderrally.com/about-go-west

 

From Tahiti to Tonga

Squash zone in this area is now fading.  An active trough is expected to reach Tonga around 27-28 Oct UTC followed by a period of NW winds, avoid.

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

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

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

14 October 2018

Bob Blog 14 Oct

WEATHERGRAM

YOTREPS

Compiled Sun 14 Oct 2018

 

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.

 

I’m back “on deck” in Auckland and available to help those voyaging the South Pacific

In early October the Australian and South Pacific Cyclone centres issue their preliminary outlooks for the coming season:

The Burau of Australia headline is: Lower number of cyclones likely for Australia

Then they posted a rather confusing graphic at

www.bom.gov.au/climate/cyclones/australia/

To understand how the graphic's numbers fit in with the headline, invert them.

SO for Australia as a whole the average is 11 cyclones and the probability of average or less is 63%.

 

NIWA say that multiple severe tropical cyclones are expected: and use the assumption that the ocean temperatures are leading into an El-Nino of the El Nino-Modoki (central Pacific based) flavour during the early part of the cyclone season.

What's an El Nino-Modoki? See www.jamstec.go.jp/frcgc/research/d1/iod/enmodoki_home_s.html.en

This tugs the South Pacific Convergence zone eastwards, thus maybe reducing the cyclone risk around New Caledonia/Vanuatu, and increasing the risk for Samoa/Cook Islands/Austral Islands..

 

NIWA in New Zealand came up with following graphics:

www.niwa.co.nz/climate/southwest-pacific-tropical-cyclone-outlook/southwest-pacific-tropical-cyclone-outlook-october-2018

 

The Pacific Islands Climate Outlook Forum was held over the last few days in Nadi Fiji to help prepare for the coming cyclone season and their outlook statement is imminent.

 

Next, a quick look at the current cyclones:

After several very busy weeks, including MICHAEL over Florida in the past few days (with devastating storm surge at Mexico Beach), tonight: all we have is LUBAN over Yemen and Strom(from the Tropics) LESLIE over Portugal.

 

 

Looking at the weekly rain maps, from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif ,

last week’s shows the path of MICHAEL and SERGIO around North America, a build-up of activity between India and Indonesia, an easing in activity around Micronesia, and much the same elsewhere.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is sitting over northern Coral sea and northern parts of Vanuatu and on-and-off to north of Fiji. It is expected to drift south towards Fiji late this week. A tropical low may form on this zone early next week and then travel eastwards towards Samoa.but then fade again by mid-next-week.

 

Subtropical ridge (STR)

It looks like the next two weeks are likely to be dominated by a BFH (Big Fat High).

A BFH has formed in the Tasman Sea and is a slow-mover with a squash zone of enhanced SE/E winds and larger swells on its northern side, peaking around southern Tonga and just south of Fiji on Monday.

From Tuesday to early Thursday (UTC) the BFH is expected to weaken around NZ as a passing trough from the Southern Ocean travels across southern and the eastern NZ. This should also weaken the squash zone north of the BFH (yea).

Then the BFH (and its squash zone) is expected to rebuild until around Wed 24 Oct and slowly travel eastwards getting east of NZ next week with a lingering ridge over north NZ.

 

Tropics to New Zealand

The best days this week to depart from Tonga /Fiji to NZ are Wednesday or early Thursday, when the squash zone weakens for a few days.

This is a rare example of a good weather pattern for arrival in NZ, with no troughs, and once it fades later this month, I suspect we will have a succession of troughs in the Tasman Sea -- and we should enjoy this weather pattern for what it is worth, even if it comes with a touch of a squash zone.

 

Between Tropics and Australia.

For those headed to Queensland or Coffs with the Down Under Go West Rally

A trough is hovering off the Queensland coast at present (its arrival brought damaging hail to Bundaberg area last Thursday) but should fade by Tuesday when it feels the domination of the BFH.

So, it is looking Ok to depart from Vanuatu/New Caledonia to Australia this week.

Note that a trough is expected to reach Coffs harbour area around local Sat/Sun and then fade, and then a more substantial trough is expected to reach Brisbane around wed 24 oct and to travel east, fading near New Caledonia by Fri 26 oct—so if you depart after Friday 19 Oct then that trough become a factor.

For more info about the Go West Rally go to www.downunderrally.com/about-go-west

 

From Tahiti to Tonga

Mainly OK for sailing this week, but a passing trough is expected to affect Rarotonga around local Sunday 14 Oct,

and a squash zone of strong 25+ knots SE winds may affect south of 18S from Niue to southern Tonga area on local Monday 15 Oct and from local Thurs 18 to Mon 22 Oct.

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

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

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

07 October 2018

BobBlog 7 Oct

WEATHERGRAM

YOTREPS

Compiled Sun 7 Oct 2018

 

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.

 

I know that I wrote last weekend telling you there may be not be a weathergram today,

but I managed to find time after a kava session this evening, washed down with Octopus and cassava 😊.

 

TROPICS

The number of tropical features has decreased during the past week.

The remains of LESLIE are heading for the UK.

SERIGO is heading to make landfall in Baja California.

And KONG-RAY is moving off to east of Japan.

 

Looking at the weekly rain maps, last week's shows a drop in activity around Solomon Islands and Micronesia, otherwise little change.

See: trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is sitting over Solomon Islands and expected to spread SE towards northern Vanuatu on Monday and then across Fiji on Tuesday in a coming-and -going fashion, and linger there until next week. By late Wednesday a trough should form south of Fiji, to around 30S, and this is expected to travel southeast so that it merges with the eastern side of a low from the Tasman sea crossing NZ on Friday then moving off to east of NZ. The convergence zone is likely to linger over Fiji in a stop and go fashion.

 

Subtropical ridge (STR)

HIGH weakening over northern NZ on Monday is expected to travel east along 30 to 35S reaching 140W/French Polynesia around Sat 15 local

This HIGH is NOT expected to have sufficient intensity to build a zone of strong easterly trade winds on it northern side. SO, note that is looks OK to venture from Tahiti to Tonga this week.

 

Next HIGH is expected to move in from west to south Taman Sea from Friday 12 Oct.

This should start to fade over northern NZ by Monday 15 Oct.

 

Between Tropics and Tasman/NZ/Aus.

Front/trough between Highs is expected to travel onto western South Island by Tuesday and deepen into a Low visiting northern NZ around Fri 12 Oct, and then move off to the East-south east. Avoid.

To avoid the southerly winds following this trough arrange departure from Tonga or Fiji to be after Fri 12 Oct.

 

From New Caledonia to Australia

Weather is looking OK for a voyage from New Caledonia to Australia this week.

 

From Tahiti to Tonga

With a HIGH travelling slowly just south of this route, this is a good week to do this voyage.

Note that a departure after 11 Oct may have an encounter with a passing trough and a period of changing winds on west end of voyage.

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

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

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

 

 

 

 

 

Bob Blog 7 Oct

WEATHERGRAM

YOTREPS

Compiled Sun 7 Oct 2018

 

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.

 

I know that I wrote last weekend telling you there may be not be a weathergram today,

but I managed to find time after a kava session this evening, washed down with Octopus and cassava 😊.

 

TROPICS

The number of tropical features has decreased during the past week.

The remains of LESLIE are heading for the UK.

SERIGO is heading to make landfall in Baja California.

And KONG-RAY is moving off to east of Japan.

 

Looking at the weekly rain maps, last week's shows a drop in activity around Solomon Islands and Micronesia, otherwise little change.

See: trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is sitting over Solomon Islands and expected to spread SE towards northern Vanuatu on Monday and then across Fiji on Tuesday in a coming-and -going fashion, and linger there until next week. By late Wednesday a trough should form south of Fiji, to around 30S, and this is expected to travel southeast so that it merges with the eastern side of a low from the Tasman sea crossing NZ on Friday then moving off to east of NZ. The convergence zone is likely to linger over Fiji in a stop and go fashion.

 

Subtropical ridge (STR)

HIGH weakening over northern NZ on Monday is expected to travel east along 30 to 35S reaching 140W/French Polynesia around Sat 15 local

This HIGH is NOT expected to have sufficient intensity to build a zone of strong easterly trade winds on it northern side. SO, note that is looks OK to venture from Tahiti to Tonga this week.

 

Next HIGH is expected to move in from west to south Taman Sea from Friday 12 Oct.

This should start to fade over northern NZ by Monday 15 Oct.

 

Between Tropics and Tasman/NZ/Aus.

Front/trough between Highs is expected to travel onto western South Island by Tuesday and deepen into a Low visiting northern NZ around Fri 12 Oct, and then move off to the East-south east. Avoid.

To avoid the southerly winds following this trough arrange departure from Tonga or Fiji to be after Fri 12 Oct.

 

From New Caledonia to Australia

Weather is looking OK for a voyage from New Caledonia to Australia this week.

 

From Tahiti to Tonga

With a HIGH travelling slowly just south of this route, this is a good week to do this voyage.

Note that a departure after 11 Oct may have an encounter with a passing trough and a period of changing winds on west end of voyage.

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

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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