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

11 December 2016

Bob Blog 11 Dec 2016

WEATHERGRAM
YOTREPS
Compiled 11 December 2016
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.

Any visitors to New Zealand who are thinking of doing some sailing around the
Hauraki Gulf this summer: please note that I am President of CANANZ, a group of
yachties in AUCKLAND who are interested in cruising and navigation. We are also
interested in helping visiting cruising yachts with a little hospitality, and
willing to answer questions about Auckland and the Hauraki Gulf. See our
webpage at www.cananz.org.nz for more details.

MARLBOROUGH SOUNDS
Some visitors will at present be considering whether to visit Marlborough
Sounds, and if so, when may be the best time to visit?

Some are saying that there may be a weak La Nina at least for the start of our
summer --- if that happens then it is likely that the Highs of the subtropical
ridge may linger over central NZ on late Jan to late Feb and so a trip to
Marlborough then is a good idea as Northland may get onshore easterly winds on
north side of these highs, or even get side-swiped by tropical lows. See the
ENSO plume at
www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/figure06.gif

Others are saying it may remain neutral this summer in which case the highs may
wander across NZ at a wide range of latitudes, and things may be much the same
over Northland as over Marlborough sounds, so may as well stay put. Bureau of
met in Australia are saying it'll be a neutral Summer, see
http://www.bom.gov.au/climate/enso/outlook/

I'll have a "bob each way" as to what may happen, and I think Marlborough will
be at its best late Jan to late Feb.

As for getting there, it's quicker going along west coast. However, in the heat
of the day on a quiet summer's day (passing High), when the interior of the
North Island heats us, the coast gets sea breezes that are good for sailing, and
these ROTATE CLOCKWISE around the North island favouring the east coast.

SO, each argument has its good points. If you do take the west coast then may be
doing this in a northerly flow on the back end of a High, so that's the forward
side of an incoming trough, so you'll need to be aware of a possible wind change
in a few days (this applies to east coast too, but with different timing.

The Tropics
The cyclone that was mentioned last week as possibly heading for Bangladesh is
now moving west along 13N towards Chennai in India as TC VARDAH. This can be
seen at
metoc.ndbc.noaa.gov/ProductFeeds-portlet/img/jtwc/products/io0516.gif

The models are starting to agree on the possible formation of a tropical
depression to NW of Fiji by Thursday, deepening as it travels Se across Fiji on
Friday/ Saturday and then SSE to east of NZ. Till too early to be sure, and
plenty of time for things to change.
Fiji Met Service is watching and will advise via
www.met.gov.fj/aifs_prods/20036.txt
Worth watching.

Rain accumulation weekly maps at
trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif shows the track
of TC VARDAH. The Intertropical convergence zone seems to show decreasing
activity.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
My thoughts go out to those affected by the recent Solomon Islands (and
Indonesia) quakes. Terrible and terrifying things, these natural events, killing
more than any terrorist can ever do.

There is likely to be a burst of NW winds early this week from Solomon islands
to Tuvalu --- hard to see if this is a burst from the monsoon forming over
northern Australia, but when it forms in this area in December it usually
precedes a tropical low or cyclone. Combine that with the warmer than normal
Sea surface temperatures in the region, and a good looking High in the Tasman
Sea mid-this-week with strong SE winds on its northern side and it seems logical
that a tropical Low will deepen between Vanuatu and Fiji by mid week and
possiblly deepen as it crosses Fiji later in the week. Worth watching.
Tropical accumulated rainfall for next week can be seen at windyty.com

Subtropical ridge (STR)
The subtropical high in west Tasman sea tonight is expected to travel east and
cross to north of NZ on Thursday/Friday. There should be a squash zone of
enhanced trade winds on its northern side around 20S.

A new HIGH is expected to squirt from Australian Bight into South Tasman sea on
Thursday and then across central Tasman sea and North Island on Friday and
Saturday.

Tasman Sea/NZ Area troughs.
The strong SW flow over NZ should continue Monday and weaken on Tuesday.
Another front is expected on Wed and Thursday followed by more strong SW winds
on Friday.
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