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

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.

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