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

18 November 2018

Bob Blog 18 Nov

WEATHERGRAM

YOTREPS

Compiled Sun 18 Nov 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.

 

SAM and the Polar Vortex

The Southern Annular Mode (SAM) is a parameter that measures the westerly winds that circle Antarctica. When it is positive the belt of strong westerly winds contracts towards Antarctica—so there a higher pressures and weaker winds over southern Australia/ New Zealand. When the belt moves north towards NZ, SAM becomes negative, and storms from the Southern Ocean can reach NZ.

 

One way of thinking about SAM is that it is a measure of the strength of the dam that walls the cold air over the Antarctic. When positive this wall is strong, and when negative this wall is weak and polar air can make be diverted outwards and northwards, maybe affecting New Zealand.

When SAM drops suddenly from positive to negative, there is an increased possibility of a “polar outbreak” somewhere in the southern hemisphere.

 

A light-hearted and animated presentation of SAM as one of the climate dogs that affect New South Wales may be seen at www.youtube.com/watch?v=G-S-YmE-Lkc . To meet the whole dog pack see www.dpi.nsw.gov.au/climate-and-emergencies/droughthub/information-and-resources/seasonal-conditions/climatedogs

 

A good proxy for SAM is the Antarctic Anomaly Oscillation (AAO) as seen at www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/new.aao_index_ensm.html ,this shows that SAM is forecast to dip negative this week.  It's not a huge dip, but does make SAM as negative as it was in mid-October, and if we look at the air temperature maps on a polar stereographic projection using earth.nullschool.net we can see cold air spreading north between last Thursday and tonight, turning all NZ dark green.

This helps explain the coldness of the front crossing New Zealand early this week. The abrupt temperature change helped form a tornado over the Canterbury Plains this afternoon:

see www.newshub.co.nz/home/new-zealand/2018/11/watch-witnesses-in-awe-of-massive-tornado-north-of-ashburton.html

 

THE TROPICS

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

GAJA continues west after crossing southern India during the past week.

There is also BROCHRA near 12S 84W going WSW.

Looking at the weekly rain maps, last week’s shows a split in activity over the Indian Ocean away from the equator, an easing in the activity over the South Pacific and an increase in activity over the tropical Atlantic.

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

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to weaken during the coming week and extend from east of the Solomon Islands to between Fiji and Samoa. It is likely to produce a trough that may visit Tonga mid-week and Niue area on Wed UTC, fading over Southern Cooks on Thu UTC.

 

Subtropical ridge (STR)

Since SAM is going negative , the Subtropical ridge is retreating to the north.

A High is expected to form near 25S between New Caledonia and New Zealand by mid-week and then travel eastwards to fade over Southern Tonga by the weekend.

 

Tropics to New Zealand

A series of trough and lows are expected around New Zealand this week. There should be an interlude of relative calm on local Friday.

 

Between Tropics and Australia.

OK at first, but maybe a trough travelling from Australia interior across the coast and into the Tasman sea on or around late local Thursday followed by west to southwest winds.

 

From Tahiti to Tonga

Weak trough passing over Tahiti on local Sunday, then looks Ok to go with eastly wind that may last over a week to north of 18S. Further south there is another passing trough to take into account.

 

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

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

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

11 November 2018

Bob Blog 11 Nov

WEATHERGRAM

YOTREPS

Compiled Sun 11 Nov 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.

 

HOW TO ACTIVATE A FRONT

I once send a wedding telegram along the lines of “Beware: whatever promotes upward motion can lead to frontal development”. I was reminded of this last Thursday when the front crossing the South Island turned into a monster, dropping around 700mm of rain into Cropp River (Southern Alps , between Mt Cook and Hokitika). The torrential rain mainly fell over the Southern Alps. Rivers flooded, and  the main highways were closed by slips and a washed out bridge.

 

Meteorologist know that the most important equation they need to understand is the omega equation. Basically, if you tap your barometer and it dips the you know you have falling pressure, and this is linked to rising motion/increased wind/ heavier rain. The equation explains how: it relates omega (change of air pressure over time) with changes in vorticity advection and thermal advection (I won’t explain these in much detail tonight, except that CVA (cyclonic vorticity advection) and WA (warm advection) result in negative omega (upward motion/ thicker clouds), and AVA (anticyclonic vorticity advection)/CA (cold advection) result in positive omega (sinking motion/clearing sky).

 

The recent weather event over New Zealand shows what happens when a well-defined upper trough with a strong jetstream travels eastwards faster than the associated front near the surface.

 

1. On Wednesday night, the jetstream was west of the surface front

as seen in an Isobar map 1am Thursday courtesy of MetService with red arrow showing jetstream.

 

2. Then by 1am Friday the jetstream moved on top of the front.

This was the day the front dumped its heaviest rain. There was also a “tropical pipeline” or moist conveyor belt feeding the front with moisture from the heat trough over Australia. Our own version of the pineapple express.

 

3.  And  by 1am Saturday the upper trough buckled, so that the jetstream stopped advancing over the South Island, and the front travelled off to northeast of the jetstream and decayed to a trickle.

 

Between 1 and 2, the CVA and WA reached high levels over the front, turning it into a monster (being over the Southern Alps also helped promote its upward motion). Then between 2 and 3 CVA and WA dropped off and the front faded.

 

Our global weather models have the ability to watch all these atmospheric equations with precision and can handle the forecasting of these events well in advance. Interestingly, if we add an extra 0.5 C to the air temperatures and re-run the global model, we can end up with as much as an extra 10% in the resulting rainfall.

 

Note that the subtropical ridge over the South Pacific was sufficiently north of the North Island to allow this front to spread over all of NZ. This is typical of EL NINO and is likely to become a trend over the next few months (but not the coming week). One positive response to the incoming El Nino is the hydro lake levels in NZ. Lake Pukaki was dropping in past few months but is now rising nicely: see www.meridianenergy.co.nz/about-us/our-power-stations/lake-levels

 

THE TROPICS

Latest cyclone activity as seen at tropic.ssec.wisc.edu shows that it is busy at present in the Indian Ocean.

ALCIDE is expected to fade or divert to the north of Madagascar.

GAJA is forecast to travel across southern India.

 

Looking at the weekly rain maps, last week’s shows high intensity rainfall in the Indian Ocean, and an increase in activity over the Solomon island to Samoa/Niue. and a relaxing of convection in the Intertropical convergence zone across the Pacific.

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

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is active from Solomon Islands to Tuvalu and is expected to produce a trough that should visit Fiji on Wednesday, Tonga on Thursday, Niue on Friday UTC and then go off to the SE.

 

Subtropical ridge (STR)

Unlike last week, the STR for the coming week is expected to be around New Zealand until Thursday. Another High is expected to travel across the South Tasman Sea from Saturday 17 to Mon 19 Nov.

 

Tropics to New Zealand

There is expected to be a squash zone of enhanced SE winds between Fiji/Tonga and NZ especially near 25 to 30S from Tuesday to Thursday. Further south, it looks Ok for arriving in NZ over next ten days. Trough from the south Tasman Sea is expected to spread onto South Island on Thu and then fade over the North Island on Friday.

 

Between Tropics and Australia.

Looks mostly OK, but maybe a trough offshore Coffs on Friday/Saturday with southerly winds near the coast.

 

From Tahiti to Tonga

Trough over Tonga on Thu 15 UTC and Niue/ Southern Cooks on Friday 16 UTC then travelling off to the SE. North side of this trough may reach Tahiti around Sun 18 November. Trough is preceded by NW winds and followed by a period of W /SW 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 November 2018

Bob Blog 4 Nov 2018

WEATHERGRAM

YOTREPS

Compiled Sun 4 Nov 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.

 

REVIEW OF LAST MONTH WEATHER PATTERNS

Sea Surface temperature anomalies as at start of November may be seen www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html

The eastern equatorial Pacific around Galapagos is the focal region for ENSO and is now on a steady warming trend. Cyclones have been stirring the seas between Mexico and Hawaii, making avenues of cooler surface water. There is a zone of warmer seas from Solomon Island to Samoa. Temperatures around Australia and the Tasman sea remain below average, a possible indicator of drier than normal conditions in the next month or so. Also, this should cool the southwest winds that reach New Zealand.

The Gulf Stream off the east coast of North America and the Kuroshio current off Japan still stand out but not as much as last month.

 

To see how the annual weather cycle and the seasons are working out, check the average isobar maps from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

The subtropical ridge in the southern hemisphere has intensified during October

 

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

The rain map shows extra convergence around equatorial Indian Ocean.

 

THE TROPICS

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

shows XAVIER off the west Mexico coast, and it is expected to stay offshore.

Looking at the weekly rain maps, last week’s shows an increase in activity across the equatorial Indian Ocean, and a relaxing of convection around Papua New Guinea and the Mariana Islands. 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)

High is travelling east along 25 to 35S past northern NZ from Monday to Friday and the expected to linger to east of New Zealand until early next week.

 

Tropics to New Zealand

Trough from the Tasman Sea is expected to spread onto central New Zealand by Fri 9 Nov and then stall, so that a zone of cloud and rain with light winds spreads onto northern NZ by Tue 13 to Thu 15 November. It looks OK to arrive in NZ with this trough.

 

Between Tropics and Australia.

Avoid a passing trough across the northern Tasman Sea on Wed and Thursday with light variable winds.

 

From Tahiti to Tonga

There may be a trough forming near Niue around Sunday 11 November, otherwise the forecast is for useful easterly 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

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

 

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.

 

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

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

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

 

 

 

 

 

30 September 2018

Bob blog 30 Sep

WEATHERGRAM

YOTREPS

Compiled Sun 30 Sep 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.

 

 

Note that there will be NO Weathergram next weekend (7 October).

I shall instead be on holiday in Fiji , so next weathergram is 14 October.

 

REVIEW OF SEPTEMBER 2018

Sea Surface temperature anomalies as at end of September may be seen www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html

 

The eastern equatorial Pacific around Galapagos is the focal region for ENSO and is now on a steady warming trend. Warmer than normal seas between Mexico and Hawaii have been forming a procession of tropical cyclones. There is a zone of warmer seas from Solomona Islands to Tonga. Temperatures around Australia and the Tasman sea remail below average, a possible indicator of drier than normal conditions in the next month or so. Also this should cool the southwest winds that reach New Zealand.

The Gulf Stream off the east coast of North America and the Kuroshio current off Japan still stand out as warmer than normal.

 

To see how the annual weather cycle and the seasons are working out, check the average isobar maps from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

 

The isobar maps show an intense High over that part of  Antarctica which is south of Australia. The subtropical ridge in the southern hemisphere has intensified during September.

 

Zooming into the NZ area, the 1010hP (between dark and light blue) isobar has shifted to south of New Zealand. And the 1020 has blossomed from the Aussie Bight to western Tasman Sea. .

 

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

The rain map shows extra convergence around Papua New Guinea and Solomon Islands.

The blue stripes in the North Pacific and Atlantic show the rain tracks of last month’s cyclones.

 

TROPICS

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

Map of current storms may be seen at  tropic.ssec.wisc.edu/

And we had an out-of-season cyclone LUIA in the Solomon Islands:

It has since faded away. Last time we had a cyclone in South Pacific in September was in 1950, Last time we had an out-of-season cyclone was RAQUEL in July 2015

 

Looking at the weekly rain maps (trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif), last week’s shows the rain track of TRAMI across Japan, and LIUA across the Solomon Islands. There is also a resurgence of activity along the ITCZ in the eastern North Pacific.

 

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ faded today after a burst of activity last week culminating in the brief formation of TC LIUA. There is still some activity near 13S mainly between 180 and 160E. This activity is shifting southwards and expected to visit Fiji on Wednesday as a passing trough, followed by a Southerly flow between Fiji and NZ on Thursday.

A passing trough over Tahiti is expected to travel east across Tuamotu islands by local Wednesday. Followed by increasing winds from the south-southeast.

 

Subtropical ridge (STR)

HIGH often over 1030hPa to travel east from 180 to 140W along 30 to 35S. with a squash zone of enhanced SE winds on its northern side. This squash zone is expected to be mainly north of 20S and is worth avoiding.

 

Between Tropics and Tasman/NZ/Aus.

That trough travelling south over Fiji on Wednesday is expected to morph into a Low lingering near northern NZ on Thursday and Friday, slowly travelling southeastwards. Avoid.

From around Thursday, that trough should have cleared from Fiji, so that a voyage from Fiji to NZ may be OK, but will need to go SW at first in southerly winds.

From Tonga may have to wait until Friday for OK weather for a voyage to NZ.

From New Caledonia to Australia. looks ok to go, but Mon/Tue/wed departures may encounter south to southwest winds for starters.

 

From Tahiti to Tonga

Avoid the squash zone by staying south of 20S. Anticipate a passing trough along the way early next week.

 

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

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

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

 

23 September 2018

Bob Blog 23 Sep

WEATHERGRAM

YOTREPS

Compiled Sun 23 Sep 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.

 

As an addendum to last week’s summary of time zone changes and national holidays:

Samoa also changes to Daylight saving on 30 Sep, from UTC +13 to UTC+14. This is so that Apia remains 1 hour ahead of Wellington all year round. (The only other place on the planet that uses time zone UTC+14 are the Line Islands, including Kiritimati, near equator 160W,almost south of Hawaii).

 

The state of the ENSO = neutral, with a weak hint of an El Nino

 

The Atmosphere:

El Nino and La Nina are opposite ends of the swing of an identifiable tropical influence on our seasonal weather. During La Nina we have cooler than normal seas along the equatorial eastern Pacific , and this shifts the subtropical ridge away from the equator. In El Nino, with warmer than normal seas, the subtropical ridge shifts closer to the equator- trade winds are weaker and the disturbed westerly wind so the Southern Ocean can penetrate further north. Each episode may last several months, sometime 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 May we have mainly had a negative SOI, consistent with a weak but rather persistent El Nino signature.

BoM states that “model outlooks continue to indicate El Niño is possible from late spring 2018.”

Weak El Nino  conditions 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 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 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, a warm period until July 2017, then a cool period until June 2018. Since then we have been having a warm period, but remaining less than 0.5 degrees above normal.

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

 

The International Research Institute of the Climate Prediction Centre IRI/CPC compiles data from several ENSO prediction models. The model predictions for the Nino 3.4 SST anomaly is that the seas ae likely to gradually WARM during the rest of this year, but the mean of the predications has only warming to 0.9 above normal--- not enough to be called an El NINO event (but closer to it that we have been for a while).

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

 

Latest SST anomaly map shows a large blue pool of cooler water west of South America. Also, there are warmer yellow waters appearing around the Galapagos. Not much ice (white) left in the Arctic at the equinox.

Sea surface temperatures across the Pacific on 20 Sep are at www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html

=================================================

TROPICS

The number of tropical features is reducing after that early September peak.

Map of current storms is at tropic.ssec.wisc.edu/

 

TRAMI is heading for Taiwan

And KIRK may skirt Venezuela

 

Looking at the weekly rain maps, last week doesn’t have the noticeable cyclone rain tracks that show in the previous week but shows more intense activity in the ITCZ across the Pacific and Atlantic. It also shows a resurgence of activity around the Bay of Bengal.  NZ had some passing fronts last week, but Australia… remains… dry.

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

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ has been hovering around the region between Solomons Island and north of Fiji for a few weeks, and is expected this week to drift south across northern Vanuatu and across Fiji/Tonga. By the end of the week a low may form south of Niue and travel off southeastwards, taking a passing trough eastwards along 20S reaching Southern Cooks by local Friday/Saturday.

And over French Polynesia a convergence zone is expected to help form a low near 20S 135W that moves off Southeastwards.

 

Subtropical ridge (STR)

HIGH often over 1030hPa to travel east across Tasmania on Tuesday and linger over northern NZ from Thursday to Saturday then fade to NE of NZ next week. eats of NZ travelling east along 40S. Squash zone of enhanced winds on its northern side mainly north of 20S from Wednesday to Saturday.

 

Between Tropics and Tasman/NZ.

Avoid that SPCZ travelling south over Fiji by Wednesday and the squash zone that follows. SO, there are OK voyages from Tonga/Fiji on Monday, or for fast boats on Tuesday, then it’s a case of staying put.

Trough crossing NZ on Monday and then a Low deepening east of NZ by Tue moving off on Wednesday leaving NZ bathed in SW winds.

After the High, next trough for NZ is expected over southern NZ on Sunday/Monday, then a trough from the Tasman after Tuesday next week.

 

From Tahiti to Tonga

OK to depart after convergence zone ha gone. Anticipate a passing trough along the way late this week.

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

 

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

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

16 September 2018

Bob Blog

WEATHERGRAM

YOTREPS

Compiled Sun 16 Sep 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.

 

Equinox is next Sunday:

Next Sunday, 23 Oct at 01:54 UTC marks the vernal equinox. At this point in time the overhead sun is directly over the equator, shifting from the northern hemisphere to the southern hemisphere.

 

If you check sunrise /sunset times for your place for Sun 23 Sep, you will find that these compute to something like 12hr 7mins of sunlight. This is because sunrise and sunset are defined with respect to the top limb of the sun, rather than the centre of the sun, and that adds a few minutes of sunlight to the day. You’ll find (if you look) that the day that has closest to exactly 12 hours of daylight, called the equilux, is around three days earlier than the September equinox.

 

Somehow, I was thinking that New Zealand switched to Daylight time on the fourth Sunday of September--- but no, the change occurs on the last Sunday of September, and so that’s 30 September

 

The change to daylight saving occurs on different dates for the nations around the South Pacific so I think it’s a good idea for you to have a summary for reference

 

Date Place Daylight saving time zone

30 Sep New Zealand UTC+13 (NZDT)

30 Sep Chatham Islands UTC+13h45mins (CHADT)

7 Oct Lord Howe Is. UTC+11 (AEDT)

7 Oct New South Wales, Tasmania UTC+11 (AEDT)

4 Nov Fiji UTC+13 (Fiji Summer Time FJST)

No changes in Tonga or Norfolk Island or Queensland or New Caledonia.

 

As yachts start their end-of-spring migration, with the approaching South Pacific Cyclone Season, it is also useful to have a summary of the various national holidays, as these limit available departure dates.

French Polynesia 1 Nov All Saints Day, 11 Nov Armistice day (100th year).

Cook Islands: 26 Oct Gospel day

Niue: Oct 19 to 22 Constitution day celebrations, Oct 22 is also Gospel day.

Tonga Sep 17 HRH Crown Prince Birthday, Nov 5 Constitution Day

Fiji Oct 10 Fiji Day, Nov 7 Diwali, Nov 20 Muhammad Birthday

New Caledonia Sep 24 National Day, 1 Nov All Saints Day, 11 Nov Armistice Day (100th year).

New Zealand Oct 22 Labour day.

Australia: OCT 1 Labour Day (ACT, NSW &SA), Queen’s Birthday (QLD)

=================================================

TROPICS

MANGKHUT travelled over the northern parts of the Philippines, with a death toll of at least 24 so far. It is now skirting around Hong Kong. FLORENCE weakened as it made landfall over Northern Carolina and has a death toll of 13 so far.

It is purely a coincidence that the Atlantic systems all have female names at present: The males: Gordon and Isaac have faded away

Also the Southern Hemisphere cyclone season is showing signs of a possible early start with the formation of Tropical depression ONE in the South Indian Ocean.

Map of current storms is seen at tropic.ssec.wisc.edu/

Looks like HELENE may end up over the UK this week.

Looking at the weekly rain maps we can see the tracks of last weeks’ cyclones.

There has been an intense area of rain last week over New Britain to northeast of Papua New Guinea.

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

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stay in the region from PNG to just south of the Solomons Islands to north of Fiji this week.

Trough over Vanuatu on Monday UTC travelling to south of Fiji on Tuesday UTC and fading over south-of-Tonga on Wednesday UTC.

Convergence zone over Tahiti on Tues UTC and Tuamotu Islands to Gambier Islands on Wednesday UTC. Then a Low may form south of Tahiti by end of the week travelling off to the SE and deepening, stealing the wind for Tahiti

 

Subtropical ridge (STR)

HIGH over 1030hPa to eats of NZ travelling east along 40S. Squash zone of enhanced winds on its northern side between 20 and 25S reaching peak on Tuesday UTC.

Next HIGH should move from Australian mainland into Tasman Sea on Mon/Tuesday UTC, and then fade over central NZ.

 

Around Tasman Sea, NZ.

Low1 crossing the South Island on Monday UTC Low2 is expected to be crossing the area between Fiji and NZ on Monday/Tuesday 17/18 Sep, followed by Low3 on Fri/sat 21/22 Sep. Southerly winds follow these lows.

For those sailing towards New Zealand from Fiji/Tonga/Noumea, there may be a narrow gap between these lows, so that the best-looking voyage this week maybe with a TUESDAY departure, but this does involve zig-zagging around some southerly headwinds.

Traffic going from New Caledonia to Australia have useful south to southeast winds for starters but may encounter a front and southerly winds near Australia from Thursday UTC.

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

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 September 2018

Bob Blog 9 Sep

WEATHERGRAM

YOTREPS

Compiled Sun 09 Sep 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 “Olde Man” Southerly

When a low crosses the North Island and the deepens as it moves away, the resulting southerly gale thru Cook Strait lasts for around three days. Such an occurrence is nicknamed by many Wellingtonians as an “Olde Man Southerly”. Its steadiness feels belligerent, lingering longer than desired. At this time of the year the arriving air hovers just below 10 C, but when the wind chill is taken into account is feels less than 4C—colder than the inside of a fridge. This wind has been described as “blowing straight through you” for you feels it’s cold in your bones .

 

We had an Olde Man last week and I was in Wellington to experience it. The weather map (Noon Wednesday local, courtesy of MetService) shows the low responsible.

 

Because this low is close to Auckland, I have heard some smart people claiming that the reason Wellington gets such cold southerly outbreaks can be summed up in two words: “Auckland  sucks”. The map illustrates a classic “eggbeater” with a clockwise spinning wind around the low to the east of the North Island, and a counter-clockwise spinning wind around the High to east of the South Island.

Of course another contributing factor to this Cook Strait gale is the layout of the land, with mountain chains over the South Island and the North Island, Cook strait is the right sized gap to make a “river of wind”.

 

This can be seen on windy.com and also by clicking on Wellington airport a graph of recent data may be seen showing temperature, wind and pressure profile during this “Olde man”

 

This river of wind crosses the isobars toward s low pressure.

1) The switch from Northerly to Southerly is relatively quick, with no real “calm” in between. Also the barometer starts rising hours before the northerly winds fade. image

2) It takes around 12 hours for a SW wind to swing to a southerly and rise to a gale, along with a period of rapid rising pressure.

3) AFTER the Southerly gale starts , the pressure continues to rise, not so fast, but a steady rise from 1015 to 1025hPa over 2 days.

4) Once the pressure peaks and steadies, the wind relaxes just a little. It continues to stay strong for another day or more.

5) Temperature remains much the same throughout the event with no day/night signal. Showers continue until the air dries out and dewpoint drops to below 5C.

 

TROPICS

It is now “busy time” for the Atlantic Ocean. FLORENCE is likely to make landfall in North Carolina, and OLIVIA may visit Hawaii but is expected to weaken in the process. MANGKHUT is heading to the northern Philippines /Southern Taiwan area.

The weekly rain maps show the tracks of last weeks’ cyclones with JEBI across Japan and NORMAN just missing Hawaii. Note hoe the rain associated with the low east of NZ just touched the east coast of the North Island. See www.facebook.com/MetService/videos/891981477639175/

There has been very intense rain associated with a low just south of Tahiti – I’m not sure why this low was so wet.

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

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stay in the region from PNG to just south of the Solomons Islands to north of Fiji this week.

Low to south of Tahiti is expected to go south and fade next few days.

Passing trough to south of Fiji on Monday UTC and then over southern Tonga on Tuesday UTC and Southern Cooks on Thursday UTC, consisting of erratic winds and possibly a few showers.

 

Subtropical ridge (STR)

HIGH less than 1020hpa is expected to form near 25S South of Tonga on Monday UTC and travel east along 20 to 25S to be south of French Polynesia by Wednesday UTC.

HIGH over 1025hPa over New South Wales on Monday UTC spreading east along 30 to 35S reaching NZ around Thursday UTC and then spreading further east along 35S. There may be a zone of enhanced SE wind so the north side of this High, mainly near 20S.

 

Around Tasman Sea, NZ.

Low is expected to cross northern NZ on Monday and southerly winds following this feature are likely to affect area between NZ and 20S on Tuesday --upsetting sailing between topics and NZ, but OK going t’other way. After that, with high pressures over NZ and trade winds to north of NZ, some good-looking sailing voyages from the tropics to NZ are likely.

Mainly easterly winds in North Tasman sea, so OK to sail New Caledonia to Australia, but not the other way. Traffic going from Australia to NZ may need to get to at least 35S to find a way eastward.

 

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

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 September 2018

Bob Blog 2 Aep 2018

WEATHERGRAM

YOTREPS

Compiled Sun 02 Sep 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.

REVIEW OF AUGUST  2018

Sea Surface temperature anomalies as at end of August  may be seen at www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html

The eastern equatorial Pacific around Galapagos is the focal region for ENSO and is now on a steady warming trend. Temperatures around Australia to New Zealand are becoming below normal, a possible indicator of drier than normal conditions in the next month or so.

The Gulf Stream off the east coast of North America and the Kuroshio current off Japan still stand out as warmer than normal.  These may help steer tropical features away to the northeast.

Warm anomalies continue off west side of Mexico to Hawaii indicating a busy cyclone season for next few months.

===

To see how the annual weather cycle and the seasons are working out, check the average isobar maps from www.esrl.noaa.gov/psd/map/images/fnl/slp_30b.fnl.html

Average isobars for past 30 days and their anomaly:

The isobar maps show that subtropical ridge in the southern hemisphere is looking robust, as are the North Atlantic and Northeast Pacific HIGHS. The August lows in the Southern Ocean have been favouring three positions: Tasman Sea, SW of South America, and SE of South America.

Lower than normal pressures between Europe and Philippines show a more active monsoon. 

Zooming into the NZ area, the 1010hP (between dark and light blue) isobar has shifted from Christchurch to Gisborne.  And the 1015 has retreated off Tonga.  This explains the increase in westerly winds onto western NZ, and can be taken as an early start to SPRING weather patterns. Not much change around Australia .

====

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

The rain map shows extra convergence in the ITCZ from Bangladesh to Philippines , and across  the North Pacific Ocean, but it has been drier than normal over the Caribbean..

In the Southern Hemisphere a large dry region stretches from Australia to Vanuatu/Fiji.. It seems that the SPCZ has shifted northwards and estwards (an El Nino trait).

In summary, it seems that, although the atmospheric and oceanic parameters are “neutral” at present, as seen in my last week’s blog, there are also some signs of an El NINO weather pattern.

 

TROPICS

We have reached the time of the year when cyclones cluster, as is happening this week in the northeast Pacific Ocean. 

 For Map of current storms see tropic.ssec.wisc.edu/

There is MIRIAM, NORMAN , and OLIVIA in NE Pacific, FLORENCE in north Atlantic, and JEBI in NW Pacific.

NORMAN is expected to sideswipe Hawaii later this week.

And JEBI is expected to visit Japan this week

 

Looking at the weekly rain maps we can see that the Asian monsoon is active over south China and the Philippines/Indonesia area, and the ITCZ is active across the northeast  Pacific and around Panama. South Pacific Convergence zone is weak and further east than normal.

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

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stretch from PNG to the Tuvalu/Tokelau area this week.

Passing trough over southern Vanuatu on Monday and Tuesday is expected to extend SE on Wednesday into a trough southwest of Fiji, the on Thursday turn into a low south of Fiji that then should go SSE to east of NZ.

Trough is expected to form over Tahiti area by local Tuesday, the convergence zone associated with this feature is expected to visit Tuamotu Archipelago to Gambier group around local Wednesday. 

 

Subtropical ridge (STR)

Large High 1035+ at 35S to south of Tahiti should fade and travel east by end of the week.  The squash zone of enhanced easterly winds between it and the Low over Tahiti should peak around mid-week with strong wind and large swells affecting Southern Cooks.  Avoid.

HIGH travelling east across Tasmania on Monday should skirt around south end of NZ on Tuesday and then travel east along 45S to east of NZ on Wednesday.  Squash zone between this high and Lows to east of the North Island should bring a classic “olde man southerly” to central NZ from Monday night until Thursday.

 

Around Tasman Sea, NZ.

High pressures in central Tasman sea this week should ensure good voyages from New Caledonia to Queensland. Traffic going from Australia to NZ may need to get to at least 37S to find a way eastward.

Low is expected to be crossing North island don Monday followed by three days of strong SE winds.  Conditions should be OK again around Friday or Saturday for departing Northland, As for sailing to NZ from tropics, nope, too much southerly this week.

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

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).

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26 August 2018

Bob Blog

WEATHERGRAM

 YOTREPS

 Compiled Sun 26 AUGUST 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 = neutral

 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.

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 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 May 2018.  Ove the last three months we have been having another warm period. 

 

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 gradually WARM another half a degree during the rest of this year, and then relax slowly next year.  The most likely period for this parameter to reach +1 and be called an EL NINO is NDJ (November December January).  And that is the early part of our South pacific cyclone season.

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

 

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 ofisobars 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.

 

For the past year the SOI has been mostly around plus 0.5 to plus 1.0, consistent with a weak but rather persistent La Nina. However, there have been several brief periods of negative SOI over the past six months and we are having another of these at present, indicating that there is a tendency towards an El Nino.

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

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

 Latest SST anomaly map shows the remains of a large blue pool of cooler water across the central equatorial Pacific. Also, there are warmer yellow waters appearing around the Galapagos.  The  Australia/Tasman Sea is getting colder than normal at the coldest time of the year, and so is the Humboldt current off western South America.

Sea surface temperatures across the Pacific on 23 Aug is at  www.ospo.noaa.gov/Products/ocean/sst/anomaly/index.html

 

In Summary: We are neutral but watching as parameters trend towards an el Nino. There is a good chance of a weak EL NINO for the turn of the year.  This should weaken the trade winds, allowing the South pacific Convergence zone and subtropical ridge to shift to the north a little--- this may disrupt cyclone formation to the east of the norm, somewhat lessening the likelihood near Australia and increasing it in the Fiji /Samoa area.  Still too early to be sure of this, so just keep it on the backburner for now, and don’t make any decisions based on that idea just yet.

  

TROPICS

TC LANE brought wind and rain to Hawaii, much as forecast. There are a couple of tropical depressions that seem to be vaguely moving westwards or north-westwards.

 After a week of heavy rain over Japan and Korea, the North Pacific is relaxing now,  and the Atlantic continues to remains quiet.

 Looking at the weekly rain maps we can see that the Asian monsoon is active between India and the Philippines, and the ITCZ is active across the Pacific and around Panama. South Pacific Convergence zone is weakening.

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

 

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

 The SPCZ is expected to stretch from PNG and Solomon Islands to Samoa and from there to the southeast.  

 Broad trough to east of NZ is expected to travel eastwards and associated passing trough should reach Society Island around local Tuesday and Tuamotu Archipelago around local Wednesday.

 There is a jetstream over New Caledonia tonight and this is expected to combine with a trough deepening east of Australia on local Monday to form a trough over Vanuatu on local Tuesday, reaching Fiji on local  Thursday and southern Tonga on local Friday.

Subtropical ridge (STR)

 HIGH crossing NZ tonight is expected to is expected to move east along 35S to 40S this week and intensify to over1040hPa by end of the week. A squash zone of enhanced trade winds on the north side of this high is expected to peak along 12 to 20S between Tahiti and Tonga from local from local Tuesday to Saturday.  Avoid.

 This squash zone detracts from a comfortable voyage from Tahiti to Tonga this week., unless  you skirt around it via Suwarrow and avoid its peak on local Thursday.

 From Thursday to end of the week, Another HIGH is expected to travel east from Australia to South of Fiji along 30 to 20S.  Small squash zone is expected in Coral Sea on the northwest side of this High.

  

Around Tasman Sea, NZ to tropics.

Passing High with light winds on Monday.    Low is expected to deepen in Tasman Sea bringing strong northerly winds to northern NZ on Tuesday, then a front on Wednesday, and then the LOW over central NZ on Thursday and Friday.   It’s a stay at home week for NZ yachts, but there are good voyages from Australia to New Caledonia.   If sailing to NZ avoid the Wednesday front.

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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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