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

29 November 2015

Bob Blog 29 Nov

WEATHERGRAM

YOTREPS

Issued 29 November 2015

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.

 

Tropical Cyclones

That tropical depression we were following last week has deepened into a Category 1 tropical cyclone TUNI.  Tropical cyclone TUNI is tonight moving toward the Niue area.

See Fiji Meteorological service at http://www.met.gov.fj/aifs_prods/65648.

html

Last week we also had Tropical Cyclone SANDRA making landfall on Baja California soon after Thanksgiving/Black Friday. –mainly as left over rain.

The origin of this cyclone was a Tehuantepecer (wind burst funneled by mountains)

(see https://en.wikipedia.org/wiki/Tehuantepecer) earlier in the week. 

See https://youtu.be/TvDT6gsTo8A for a windyty.com view of this metamorphic event.

 

The Weekly rain maps show rain concentrations in TUNI and SANDRA during

the past week.  

Weekly rain signatures are seen at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

SPCZ=South Pacific Convergence zone.

The main part of the SPCZ is strong in activity and extends from Tuvalu to TUNI (between Samoa and Niue) and has squally NW winds on its northern side. There is another branch along 15S across the Cooks and French Polynesia with N/NW winds on its northern side and SE winds on its southern side. 

 A low centre is expected to form on Monday UTC/Sunday local, near 15S 153W, close to the north side of Maupiti/Mopelia (Maupihaa) and this compact feature MAY develop into a cyclone over Tahiti area by mid-week.  The models are forecasting large swells around this feature. Brace accordingly.

 

STR= Sub-tropical Ridge

The STR is very strong this week with well-marked and slow-moving HIGHS.

A HIGH is crossing central NZ this evening and should travel slowly along 45 to 40S this week, further south than normal.

Another HIGH is expected to envelop the Aussie Bight mid-week and then move into the Tasman Sea on Friday.

 

Over NZ/Tasman:

Trough preceded by NW winds and with a southerly change reaching Sydney around local Wednesday morning and then Northland by late Friday, then fading away.

 

Travelling Tahiti to Marquesas. 

Convergence zone between Tahiti and Marquesas is too squally, and there is this tropical depression/possible cyclone forming on local Sunday. 

Best to stay put and tune in to local warnings and brace for strong winds/swell this week.

 

Between Tropics and NZ:

The lingering High makes travelling from New Caledonia to NZ OK, and should be OK when the wind/swells of TUNI ease around Fiji/Tonga.

>>>>>> 

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com. Tell anyone you like that to subscribe they should email me.

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 subscribe.

To unsubscribe,  send a reply email saying LEAVE.

 

 

22 November 2015

Bob Blog 22 Nov

WEATHERGRAM

YOTREPS

Issued 22 November 2015

 

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 ICA seminar week in Opua (and there was one in Newcastle too) went well.

Thanks to all those sailors that attended my seminar on Friday afternoon.

It was great to meet with you and get your feedback—some of the stories you told were priceless and worthy of writing up.

 

El Nino:

The weekly value of Nino3.4 was measured last week to reach 3.0 C (above normal)

As seen at http://arstechnica.com/science/2015/11/el-nino-reaches-record-level-for-a-single-week-period/

This is a record reading, but it is the monthly NINO3.4 reading that counts, and also there are other ways of measuring El Nino.

Perhaps the broadest parameter is the Multivariate ENSO index which uses both atmospheric and oceanic data, as seen at

http://www.esrl.noaa.gov/psd/enso/mei/rank.html, is plateauing at 65.  It reached 66 in the 1997/98 and 1982/83 El Nino episodes.

The current El Nino episode is predicted to peak during the next three months and ease to neutral by mid-2016.

 

Tropical Cyclones:

Tropical cyclone features may be seen at http://tropic.ssec.wisc.edu/ Last week we had a set of twin tropical depressions near 170E.

The one in the southern hemisphere (93P)went west across northern Vanuatu and into the Coral Sea.

The one in the northern hemisphere (95W) also went west, taking it towards the Philippines – it now has the name In-Fa and is expected to re-curve and stay out at sea.

In the south Indian Ocean TC ANNABELLE is expected to travel south near 70E.

And in the warmer than normal seas off Mexico’s west coast tropical depression RICK is expected to travel north near 120W.

The Weekly rain maps show convection traveling southwards from the equator into the southern Indian Ocean and into the  South Pacific Ocean.

These can be seen at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The main part of the SPCZ is strong in activity and extends from Solomon Islands to Samoa, with a dip south towards Fiji.

A tropical LOW is likely to form on this zone north of Fiji by mid-week and then travel across the Samoa/Northern Tonga region by end of the week, very likely bringing squally rain and possibly bring strong winds. This may be a hazardous feature so if you are in the area keep close tabs on its progress, and take adequate precautions in advance.

 

STR= Sub-tropical Ridge

The STR is very strong this week. A HIGH is expected to travel across northern NZ on Monday and then linger to east of North island for the remainder of November and into early December. Fronts crossing the Tasman Sea are likely to be diverted by this strong High so that they travel onto to the South Island.

 

Over NZ/Tasman:

Disturbed west to NW flow south of Northland with occasional fronts.

 

Travelling Tahiti to Marquesas.

Easterly winds are expected to turn and be from NE by end of this week, and maybe NW next week. Active convergence zone with squally showers is expected to lie in-between Tahiti and Marquesas by end of this week.

 

Between Tropics and NZ:

The HIGH lingering to east of North Island from this week into around mid- next-week gives a great opportunity for sailing to NZ from Tonga/Fiji/New Caledonia.

>>>>>> 

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com. Tell anyone you like that to subscribe they should email me.

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 subscribe.

To unsubscribe send a reply email saying LEAVE.

15 November 2015

Bob Blog 15 Nov

WEATHERGRAM

YOTREPS

Issued 15 November 2015

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.

 

Equatorial Twin tropical lows

There are no tropical cyclones at present, but two tropical lows are twinning near 170E.

In the north is 95W and this is expected to peel off to the west and then recurve before reaching Philippines.

And 93P in the south should travel south across Vanuatu this week then turn into a trough that is expected to reach Fiji to Minerva by Friday and maybe Tonga on Saturday. 

 

Weekly rain maps at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif show build ups of convection around India and in the South Pacific to north of Fiji.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The main part of the SPCZ is expected to linger from PNG to Vanuatu and from Tuvalu to Samoa.  There is also likely to be some squally rain with the low /trough associated with 93P.

 

STR= Sub-tropical Ridge

The STR is stronger this week than last week with large slow-moving highs.

  One to NE of NZ on Sunday is expected to travel along 30S. Another is crossing Tasmania on Sunday night local and cross the Tasman Sea on Monday Tuesday, then NZ on Wednesday, and off to the NE of NZ from Thursday.

 

Over NZ/Tasman:

A weakening front is expected to cross northern NZ on Monday followed by a SW flow on Tuesday. Next front is expected to cross northern NZ on Friday followed by a weak ridge on Saturday and another front on Sunday 22 Nov. 

 

Travelling Tahiti to Marquesas. 

Easterly winds.   Active convergence zone with squally showers lies in-between.  

 

Between Tropics and NZ:

OK for departing from Fiji/Tonga early in the week, so long as you arrange arrival in NZ to avoid the front and SW winds expected on 22/23 Nov. 

After around Tuesday, take into account the track of that tropical low over Vanuatu. 

Its trough is expected to reach Fiji to Minerva by Friday, and the NE winds and squally showers that precede this trough may reach Fiji to Minerva by late Thursday.

>>>>>> 

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com. Tell anyone you like that to subscribe they should email me.

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 subscribe.

To unsubscribe, send a reply email saying LEAVE.

 

 

08 November 2015

BOB BLOG 8 Nov

WEATHERGRAM

YOTREPS

Issued 8 November 2015

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.

 

El Nino is strong and increasing and about to get as strong as it was in 1997/8

 

This can be seen by looking at the sea surface temperatures for the NINO3.4 area in eastern equatorial Pacific, at http://farmonlineweather.com.

au/climate/indicator_enso.jsp?c=nino34&p=monthly.  There is now ample excess energy stored in the ocean, ready to be released into the

atmosphere by “teleconnections” to activate storms and prolong droughts.

 

 

Merging Lows to NE of NZ last week

The Low that crossed NZ last Wednesday (its frontal rain arrived in time to greet the All blacks as they arrived at Auckland Airport , and its

southerly gale greeted HRH The Prince of Wales in Wellington all of Wednesday) danced with and then was taken over by a smaller  smaller low

to the north.  This is what meteorologists call the Fujiwhara effect, see https://en.wikipedia.org/wiki/Fujiwhara_effect.   I wasn’t able to

capture the satellite imagery, but here’s the Windyty animation--- but I suspect the models haven’t captured the event as it really occurred. See

https://www.youtube.com/watch?v=TdQOmaYV508&feature=youtu.be

 

TROPICAL TOPICS

Following close of the heels of CHAPALA from last week, tonight we have MEGH heading for Yemen. See  http://www.tropicaltidbits.com/storminfo/

 

Weekly rain maps form http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif show that the main part of the convection in the Indian Ocean has spread east in the past week.

This eastward trend ( MJO cycle) seems to be on track to move across northern Australia by end of November and into Coral Sea area maybe by

mid-December. SO the risk of tropical cyclone formation in the south Pacific is expected to remain low for the next few weeks according to

that observation.

The maps also show the South Pacific convergence zone has spread out since last week and become more diffuse but covers a wider area.

 

WEATHER ZONES

SPCZ=South Pacific Convergence zone.

The main part of the SPCZ is expected to linger from north of Vanuatu to Samoa with a branch towards French Polynesia. However, just as it did

last week, some of its convection is likely to drift south—moving onto northern Fiji especially from Thursday to Sunday, and maybe northern

Vanuatu as well.

 

STR= Sub-tropical Ridge

The strong HIGH that arrived in the South Pacific last week is expected to continue moving east this week along 40S well to the east of NZ. 

Central Australia is now so hot that the HIGHS are shunning it (hot air=low pressure) and thus travelling across the Australian Bight and south

of Tasmania. The next incoming HIGH is expected to be doing this by mid-week and then travel around southern NZ on Friday. It is also expected to

intensify on Friday, thus producing a squash zone of SE winds on its northeastern side= a SE wind burst. This squash zone should spread north

on Saturday and Sunday—as far north as 28S.

 

Over NZ/Tasman:

A weakening front is expected to cross the North Island on Monday followed by a SW flow from Tuesday to Thursday and a SE wind burst early

on Friday. The next front in the Tasman Sea is expected to deepen into a LOW on Sun 15 Nov that crosses North Island on Mon 16 Nov.

 

Travelling Tahiti to Marquesas.

Easterly winds and minor convergence zones.

 

The Island Cruising Association is holding the All Points rally to Opua and the Downunder rally from Noumea to Newcastle.

Between Tropics and NZ: for the All Points Rally, ending in Opua:

It is the time of the year that analysis paralysis sets in at the Minerva Yacht club.

The SE wind is expected to return to Minerva for Sat/Sun 14/15, otherwise just light SW/SSW/S winds there this week, and outlook is for light NE/E

winds there for much of next week.

Its difficult to decide when to go when there are either SW winds or large wind holes partly affecting the way from Tonga to NZ.  Well at this

stage next week may have even larger wind “holes” so perhaps some of the second class patterns of this week should be chosen rather than waiting

too long – I can produce some waypoints for you to guide you around the holes and SW zones, but they will take longer than going direct.

The only lot of strong winds that I can see this week is to do with that squash zone over NE NZ on Friday 13 – moving off to the NE on Sat 14—and

it is easy enough to avoid by going well enough west around it.

Looking ahead, there are likely to be strong N/NW winds on Mon 16 Nov with that passing Low, and these may extend north of NZ to around 30S. At

least they are tailwinds for incoming yachts.

 

Between Tropics and Australia

For the Downunder Rally (Noumea to Newcastle)

I’m informed that 75% have arrived and 25% are in transit.

Avoid arriving in Newcastle when a front /low passes by the area on late 12/13/14 Nov and again on 17/18 Nov.

>>>>>>

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com. Tell anyone you like that to

subscribe they should email me.

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 subscribe.

To unsubscribe send a reply email saying LEAVE.

 

01 November 2015

BOB Blog 1 Nov 2015

WEATHERGRAM

YOTREPS

Issued 1 November 2015

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.

 

Tropical cyclone genesis and occurrence: A weekly treasure:

The Meteo France weather Office in Noumea have started a page on their web site which translates the latest phase of the MJO (Madden Julian Oscillation= a quasi-cycle that travels from the Indian Ocean across Northern Australia to western pacific around once every 3 to 6 weeks, encouraging extra convection) into maps showing the probability of occurrence or genesis of tropical cyclones. These can be found at http://www.meteo.nc/cyclone/coin-des-experts (then click on the example graphics to get the latest).

These maps show that the MJO is active in the Indian Ocean at present—and this implies that it may get to the western South Pacific late this month or early December.

I suppose this means that there is no immediate hurry for departing the tropical South Pacific. However If your marine insurance becomes void in the cyclone season (and many Insurance Companies define that as from 1 November for South Pacific) then your financial risk has risen overnight.

 

TROPICAL TOPICS

In tune with the MJO, there is just one active tropical cyclone at present and it’s near the horn of Africa. CHAPALA, heading for Yemen. See http://www.tropicaltidbits.com/storminfo/

 

The Weekly rain maps, as seen at http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif,

show steady convection over western part of Indian Ocean, and a weakening over the whole Pacific Ocean.

 

WEATHER ZONES

 

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to have a reasonably quiet week mainly near Solomons to Tuvalu and Tokelau, with scattered convection over Southern cooks/French Polynesia. There may also be some shower activity for Wallis and Futuna.

 

STR= Sub-tropical Ridge

The axis of the STR is strong along 30S from north of NZ to south of Pitcairn Island. Strong enough to provide a zone of light winds for yachts heading to NZ from the tropics. Nothing much can be done about this except for motoring in light winds. The pattern seems to be in place until at least mid-month.

The HIGH that is in the Australian Bight tonight should cross south of Tasmania on Tuesday and then travel NE across the Tasman Sea and stall over northern NZ from Sat to Tues 10th and then be replaced with another High keeping a ridge over or to north of northern NZ from Wed 11 to Sat 14 Nov.

 

Over NZ/Tasman:

The front moving NE over southern NZ on Monday is expected to receive a developing low from Australia on Tuesday and deepen this over central NZ on Wednesday so that the low hovers to east of the North Island from Wed to Friday (an olde man southerly), and the lingers off to NE of North Island from Sat to Mon 9 Nov (cut off upper low).

There are likely to be SW winds partly on the way between NZ and Tonga from Thursday to Sat 9 Nov.

 

Travelling Tahiti to Marquesas.

Easterly winds and minor convergence zones. May be NE winds locally over Tahiti on local Sunday/Monday.

 

Travelling Tahiti to Tonga:

The SPCZ should stay north over most of this route and is weak over Tahiti.

No squash zones this week. A trough is expected to travel from Tonga to Niue this weekend, Sat/Sun 7/8 Nov UTC, bringing light variable winds, maybe some SW winds and a few showers.

 

The Island Cruising Association is holding the All Points rally to Opua and the Downunder rally from Noumea to Newcastle.

Between Tropics and NZ: for the All Points Rally, ending in Opua:

A weak trough is expected to form over the Minerva area on local Thursday and travel to Tongatapu by Friday night, with variable light winds, and followed by a period of SW/S winds--- This isn't a major problem but does take the edge off the comfort of any departures from Tonga on Thursday and Friday.

Departures from Tonga (and sometimes Fiji) to NZ this week have some S/SW winds to divert around, especially from Thursday to Saturday—and this can be done by going far enough WEST before the southerlies and encountered, but does slow and lengthen the voyage.

Departures from Fiji and New Caledonia have that subtropical ridge axis to cross—a zone of no wind near 28 to 30S.

AT this stage, looking 5 days plus ahead, it seems that there are no dates to avoid for arrival in NZ, but onshore easterly wind are expected over NE NZ on Tuesday 10 November so maybe avoid that day.

 

Between Tropics and Australia

For the Downunder Rally (Noumea to Newcastle) Hmmm. A Low from the heat of the interior of Australia is expected to travel east along 35S across New South Wales and into the Tasman Sea on Thursday bringing a SW change into Newcastle on Friday 6 Nov. This may not be a gale—but the rain (mainly on Wednesday) should be squally.

The associated trough should weaken quickly but linger along 30S.

Departures from Noumea this week before Thursday are likely to just encounter some of that left-over trough near 30S. On Monday 9 Nov there may be STRONG northerly winds and squally rain near 30S – avoid.

>>>>>>

 

See my yotpak at boatbooks.co.nz/weather.html for terms used.

See my website www.metbob.com for information on tailor-made voyage forecasts– Feedback to bob@metbob.com. Tell anyone you like that to subscribe they should email me.

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 subscribe.

To unsubscribe send a reply email saying LEAVE.

 

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