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

31 December 2017

Bob Blog 31 Dec 2017

WEATHERGRAM

YOTREPS

Compiled Sun 31 December 2017

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.

Happy New Year to all my readers.

In the words of one of the lesser known verses of Auld Lang Syne:

+++++++++++++++++++++++++++++++++++++

We too have paddled in the stream

From morning sun to night

But the seas between us broad have roared

+++++++++++++++++++++++++++++++

 

The Tropics:

Last week we mentioned TD 92S in the Timor Sea and it deepened into TC HILDA and made landfall over NW Australia near Broome.  The first this season.   It is now a rain depression in the interior of Australis, filling in as it heads to Melbourne.

There are some other small tropical depressions in the NW Pacific and in the Indian Ocean, but NO tropical depressions are expected in the coming week in the South Pacific.

Looking at the weekly rain maps from last week and the week before, as at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif,

we can see pockets of intense convection over NW Australia associated with HILDA,

and decreasing intensity everywhere else.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is still active to east of 180, but rather weak over the Coral Sea and Northern Vanuatu 

 

Subtropical ridge (STR)

HIGH1 well to east of NZ near 45S 160W is expected to blossom this week and slow down the progress of the trough on its western side (over NZ).

The next HIGH to the west, H2, should still be in the Aussie bight o Wednesday, and is expected to travel east across the central Tasman sea on the weekend of Sat 6/7 Jan, but may weaken in transit.

Low visiting northern Tasman/NZ later this week.

Trough is crossing Tasman Sea this week. 

Small low is expected to cross central NZ on Monday and Tuesday.

Another Low is expected to deepen in northern Tasman on Wednesday

and deepen further as it travels southeast across northern NZ on Thursday and Friday,

then slowly weaken. Avoid.

 

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24 December 2017

Bob Blog 24 Dec 2017

WEATHERGRAM

YOTREPS

Compiled Sun 24 December 2017

 

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.

 

Merry Christmas to all readers of this blog…

 

The Tropics:

This current period of increased risk of cyclone formation, due to a passing MJO , has now peaked and should decline next week. It has produced quite a crop of cyclones, mainly in the northern hemisphere. TC KAI-TAK has gone off west of Philippines and is fading away over central SE Asia. TEMBIN is visiting Philippines and has been vicious, with a death toll of more than 180, at this special time of year. Makes me feel their family's sorrow.

 

The next one for the northern hemisphere is 98W, which is currently located as a weak feature very near the equator, sort of defying the principle that weather features can not rotate at the equator.

 

In the southern hemisphere we have has a Low TD93P within the South pacific Convergence zone for the past few days, and Fiji Met have been keeping a close eye on it. It now seems to be starting to weaken and is expected to travel Southeast.

 

That leaves TD 92S, very weak at present in the Timor sea a, and this may deepen as it travels southwest over next few days, and may make landfall over northwest Australia mid-week.

 

Looking at the weekly rain maps from last week and the week before, at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif, we can see pockets of intense convection around SE Asia, Philippines and northeast of Papua New Guinea, corresponding to Kai-Tak, Tembin and TD98W.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

There are no more near-equatorial westerlies —a sign that this MJO is peaking and will the SPCZ will soon relax.

The SPCZ has split into two zones… an eastern zone of active convection that is being taken off to the southeast by TD93P, and a new zone of building convection over the Coral Sea.

 

93P is expected to travel SE to south of Fiji, reaching Minerva area on Boxing Day. Avoid.

 

Subtropical ridge (STR)

HIGH to east of South Island is moving off to the east.

New HIGH is expected to travel east across Tasmania on Tuesday/Boxing day and then onto South Island on Thursday, and then east along 45Souh to east of NZ.

 

Troughs over NZ:

Trough/cold front is expected to cross South Island on Monday and North island on Tuesday, followed by a South to Southeast wind flow, and deepening into a low east of the North Island on Wednesday, travelling east along 35 to 30S with large SW swells following it. With all these southerly winds from Tuesday afternoon, avoid the Hawkes Bay/Gisborne coast.

Looks Ok for Auckland yachts heading north after Christmas after the front’s peak winds on Boxing Day morning.

 

Next trough, following the next HIGH, is expected to start moving from Tasman Sea onto South Island on Saturday and further east later. Anticipate a period of strengthening N/NW winds ahead of this system for several days.

 

Sydney-Hobart

As the Tuesday Tasmanian high travels off to the east, expect an increasing NE flow on its back end, with thermal fluctuations to the wind direction along the coast.

Warm front on Friday and cold front with west/SW change on Saturday.

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Feedback to bob@metbob.com or txt 6427 7762212

I’m on Facebook at /www.facebook.com/metbobnz/

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, Click FOLLOW at bottom right.

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22 December 2017

Bob Blog 23 Dec 2017

If you are in the Fiji/Tonga area over the next few days then keep an eye on TD04F

 

at   www.met.gov.fj/aifs_prods/20036.txt

 

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Tropical Disturbance Summary For area Equator to 25S, 160E to 120W

ISSUED FROM RSMC NADI Dec 220836 UTC.

 

TROPICAL DEPRESSION TD04F [1000HPA] WAS ANALYSED NEAR 16.3S 173.5E AT

220600UTC. TD04F MOVING SOUTH-SOUTHEAST 10 KNOTS. POSITION POOR BASED

ON HIMAWARI-8 EIR SATELLITE IMAGERY AND PERIPHERAL SURFACE

OBSERVATIONS.

 

CONVECTION REMAINS PERSISTENT OVER SUPPOSED LLCC. ORGANISATION

REMAINS POOR. THE SYSTEM LIES SOUTH OF AN UPPER RIDGE IN A LOW

SHEARED ENVIRONMENT WITH GOOD OUTFLOW. CYCLONIC CIRCULATIONS EXTENDS

UPTO 700HPA. SST AROUND 29 DEGREES CELSIUS.

 

GLOBAL MODELS HAVE PICKED UP THE SYSTEM  AND SLOWLY MOVE IT

SOUTHEASTWARDS WITH SLIGHT INTENSIFICATION.

 

POTENTIAL FOR THIS SYSTEM TO DEVELOP INTO A TROPICAL CYCLONE IN THE

NEXT 24 TO 48 HOURS IS LOW TO MODERATE.

 

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17 December 2017

Bob Blog 17 Dec 2017

WEATHERGRAM

YOTREPS

Compiled Sun 17 December 2017

 

Bob McDavitt’s ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the patterned world.

 

The Tropics:

We are going thru a period of increased risk for development this week, caused by a passing MJO or Madden Julian Oscillation. That is a period of increased convection that spreads east from Indian Ocean to Pacific Ocean.  Accompanying this MJO there is a burst of equatorial westerly winds  EW near Papua New Guinea and this can help  trigger cyclones at either 5 degrees  North latitude or 5 degrees South latitude – sometimes at both 5N and 5S at the same time (a process called twinning).

 

Tropical cyclone Kai-Tak is travelling west across the Philippines tonight, and tropical depression 97W is forming near 5N, also a Low is within the South Pacific Convergence zone north of Fiji.  hese features are loosely linkes with some equatorial westerly winds.

 

The South Pacific Convergence Zone SPCZ is active over northern Vanuatu to northern Fiji/Tonga/Niue /Southern Cooks, and looks ripe to be able to produce a tropical depression this week.  That feature, if it deepens, is likely to travel southeast along the SPCZ, and may get a cyclone name for a while but may only briefly reach gale /storm force. Worth watching if you are in the vicinity.

 

After next week the SPCZ should settle down, and the cyclone risk is expected to lower from late Dec to mid-January.

 

The weekly rain maps at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif ,from last week and the week before, show pockets of intense convection around Philippines and north of Papua New Guinea, corresponding to Kai-Tak and 97W.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ has SE trade winds on its south side and NW winds on its northern side, and is intense across north part of Fiji to between Samoa and Tonga to Southern Cooks. The zone has a tropical low on it, to north of Fiji tonight. This Low may deepen over next few days and then travel southeast, taking with it a lot of the extra convection. Avoid.

 

Subtropical ridge (STR)

HIGH in the north Tasman Sea is expected to fade away by Sat 23 Dec.

Another High is expected to travel from Aussie Bight to South Tasman Sea on Wed/Thu and then travel east across South Island on Friday and off to the east of New Zealand from Sunday.

 

Sailing to NZ:

A southwest flow is expected over northern NZ until that High in the north Tasman Sea fades away on Friday.

After the High in the South Tasman Sea travels off to the east of NZ (early next week), there is an opportunity for a cold front to travel east across the Tasman Sea, preceded by a NW flow that may help some yachts to get to Northland. However, during next week that front is expected to stall and fade, allowing a NE flow to establish over northern NZ and that may be tricky to deal with.

 

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

Feedback to bob@metbob.com or txt 6427 7762212

I’m on Facebook at /www.facebook.com/metbobnz/

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, Click FOLLOW at bottom right.

To unsubscribe from WordPress: click the “unsubscribe” link on the bottom of the email.

Or, if email wasn’t from WordPress then send a reply email saying LEAVE.

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10 December 2017

Bob blog 10 Dec 2017

WEATHERGRAM

YOTREPS

Compiled Sun 10 December 2017

 

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 ENSO – We are having a LA NINA—but for how long?

El Nino and La Nina are opposite ends of an identifiable tropical influence on our weather. La Nina comes with cooler than normal seas along the equatorial eastern pacific, and is associated with stronger than normal trade winds and shifts the subtropical ridge (and its jetstream) away from the equator. El Nino has weaker than normal trade winds and warmer than normal seas draws the subtropical ridge closer to the equator. So, they are like opposite tilts of a seesaw. Their comings and goings can last several months, maybe over a year, and so their status can be used to forecast the weather for the next month or so.

 

BoM, Australia, has now declared this to be a LA NINA.

The central to eastern tropical Pacific Ocean has cooled steadily over last few months and are now at the La NiƱa thresholds (0.8 °C below average). See www.bom.gov.au/climate/enso/

However, the BoM have pointed out that this La Nina may be weak and short-lived—weaker than the last one in 2010-2012. It looks stronger than the La Nina we had around a year ago.

 

The Ocean:

NINO3.4 is a region in the eastern equatorial Pacific Ocean that acts as a heat storage area during an El Nino, or becomes cooler than normal during a La Nina. This plays with the heat budget of the atmosphere and thus with the weather patterns.

At the farmonline web site we can see that since August there has been a cool trend for NONO3.4, and a few weeks ago the seas were over 1-degree cooler than normal.

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

 

Atmosphere

The 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 the placement of isobars 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 August the SOI has been more than 0.5, and for two weeks in October and one week (so far) in December it was over the +1 threshold.

This all ties in with “early start to summer” experienced in NZ, with anticyclones lingering over the Tasman Sea and New Zealand mainland, bringing periods of sunny weather and light winds. After New year, these HIGHS may shrink, but still stay near central NZ, so that there may be periods of strong easterly winds over Northland. In the South Pacific, convergence zones should be further south than normal, allowing tropical lows to form near 15South latitude rather than 10S.

La Nina 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 Models

The International Research Institute of the Climate Prediction Centre compiles data from several ENSO prediction models. The mid-November edition shows the the cluster of data from the models for NINO3.4 temperature may have bottomed out in DJF (Dec Jan feb) and start rising a little in JFM 2018, and more so in FMA.

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

 

TROPICS

No cyclones around at present.

There continues to be a burst of equatorail westerly winds from east of Malaysia to north of Papua New Guinea.

Looking at the weekly rain maps from trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif and comparing last week and the week before, we can see pockets of intense convection around Thailand and Indonesia, but weaker than last week. This cluster of extra convection is expected to make its way eastwards and start appearing in the Coral Sea area ovr next few weeks. This is called an MJO (Madden Julian Oscillation).

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is hovering over the Coral Sea to south of Solomon Islands to Samoa to Southern Cooks. The low that is tonight at the end of the SPCZ and south of the Southern Cooks is expected to travel slowly south and deepen.

By mid-week a new convergence zone and Low is expected to form in the Coral sea, and by next weekend this Low may deepen as it travels from Vanuatu to Fiji, with SPCZ over Tonga. Avoid these developments.

 

Subtropical ridge (STR)

HIGH H1 is expected to travel east along 40S from south of Southern cooks tonight to south of Pitcairn island by end of this week.

HIGH H2 is forming in South Tasman Sea by Tuesday, and expected to travel onto southern NZ on Wednesday and stretch from North Tasman Sea across central NZ to south of Chathams by Friday. Then it may stall for a few days, or perhaps weaken away.

 

Tasman Sea/NZ

I think the sailors are now resting. If you would like more detail for your voyage, then check metbob.com to see what I offer.

>>>>>>>>>>>>>>>>>>>>>>>> 

“I think my whole life has been one of sort of daring,

and sort of sailing against the wind instead of just going with the wind.”

John Lewis

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

Feedback to bob@metbob.com or txt 6427 7762212

I’m on Facebook at /www.facebook.com/metbobnz/

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, Click FOLLOW at bottom right.

To unsubscribe send a reply email saying LEAVE.

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03 December 2017

Bob Blog 3 Dec 2017b

WEATHERGRAM

YOTREPS

Compiled Sun 3 December 2017

 

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 November weather.

Sea Surface temperature anomalies may be seen at www.ospo.noaa.gov/data/sst/anomaly/2017/anomg.11.30.2017.gif

The SST anomaly image is that of a typical LA NINA, with cooler than normal sea along the eastern Pacific equator linked to stronger than normal trade winds that spread further away from the equator, so that the subtropical ridge (in both hemispheres) is further than normal away from the equator.

There appears to be a warmer than normal zone between Tasmania and the South Island—it may take a few weeks, but this can activate troughs to produce more rain.

 

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

During November the 1015hP isobar has spread from middle NZ to south of NZ 

—that’s a large jump for the subtropical ridge.

This is a strong regional change and, examining the details, there have been some similarly significant pattern changes in the northern hemisphere too. However, there hasn’t been as strong a change over South America or South Africa. So, the impact of this LA NINA has its peculiarities

 

Last 30 days of rainfall, and its anomaly, may be seen at trmm.gsfc.nasa.gov/trmm_rain/Events/thirty_day.html

We can see one of the typical impacts of this La Nina by looking at the Intertropical convergence zone ITCZ on the monthly total rainfall total and its anomaly maps. This shows the latitude of the ITCZ has been knocked to the north across the Pacific, further away from the equator, and its normal latitude is now a yellow zone of dry anomalies. But this impact is regional,  and a reversal of it is seen in the Atlantic Ocean.

 

TROPICS

TC OCKHI is currently in the North Indian Ocean heading toward NW India. It is expected to weaken before it makes landfall around Wednesday. See www.tropicaltidbits.com/storminfo/

The South Pacific Cyclone season has opened with TD 01S DAHLIA off to the NW of Australia .

This is just a tropical depression (doesn’t have a ring of gales around its centre) and is likely to fade in a few days, but does get the season-count rolling.

Models are picking that there may be another tropical depression forming in the Coral Sea this week, but it should fade as it moves towards New Caledonia.

There are some bursts or equatorial westerly winds across the Timor Sea and to north of Papua New Guinea.

 

Looking at the weekly rain maps from last week and the week before,  at trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif,   we can see an increase in convection in the equatorial Indian Ocean. This cluster of extra convection is expected to make its way eastwards and start appearing in the Coral Sea area around mid-December. This is called an MJO oscillation

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The SPCZ is hovering from Coral Sea to northern Vanuatu to Tonga to Southern cooks, with a reasonably clear gap over Fiji. Small lows are expected to form along 25South, to south of the SPCZ during mid-week. These are formed by a passing upper trough.

 

Subtropical ridge (STR)

HIGH H1 is expected to linger along 30 to 40S to east of NZ for the whole week.

Then another HIGH H2 is expected to cross Tasmania on Tuesday and southern NZ on Wednesday and then build to east of South Island from Thursday.

 

Between Tropics and NZ

A Low is expected to form between Fiji and NZ near 28S on Wednesday and fade away to the east on Thursday. This  feature is the  surface reflection of a passing upper trough  and may be reasonably easily avoided.

As H2 travels to east of NZ there should be a NE flow over northern NZ until Mon 11 Dec, providing a reasonable opportunity for getting to NZ.

After that the models differ wildly, so may be better to wait for a more solid favourable forecast.

 

Between tropics and Australia

Looks ok: The trough that is along and offshore the east coast of Australia is the one that flooded parts of Victoria over the weekend. It should fade and go off to the south by Thursday.

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“Sailing is just the bottom line, like adding up the score in bridge.

My real interest is in the tremendous game of life.”

- Dennis Conner

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

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

Feedback to bob@metbob.com or txt 6427 7762212

I’m on Facebook at /www.facebook.com/metbobnz/

Weathergram text only (and translator) is at weathergram.blogspot.co.nz.

Weathergram with graphics is at metbob.wordpress.com, Click FOLLOW at bottom right.

To unsubscribe send a reply email saying LEAVE.

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

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