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

06 July 2014

BobBlog issued 6 July

WEATHERGRAM
YOTREPS
Issued 6 July 2014
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 of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

Scott Donaldson (http://doubleditch.co.nz/Tracker) got within 36m/65km WNW
of New Plymouth in calm conditions on local Sunday morning, and then an
easterly wind developed so that he has now stopped paddling and will try and
stay-put and hunker down in a NE gale on Tuesday and Wednesday.
He may be able to start paddling again on Friday, and by then may have
drifted 30 miles to the SW of his current position. The whims of the weather
are tossing him a new adventure.

John Furnell of Helicopter Services, based in Taupo, took advantage of
todays rare calm conditions to do another airdrop to top up Scotts
supplies for the week ahead. Scott seems to still be determined to continue
kayaking, it is his adventure and he doing this adventure to support Asthma
NZ. MetBob is helping by watching the weather for him. To cheer him up drop
in a few dollars via http://DoubleDitch.co.nz.

During June the subtropical ridge STR in the Southern hemisphere was
stronger than normal and pressures in the southern ocean lower than normal,
thereby increasing the disturbed westerlies in-between  and thats an El
Nino trait. At present there is a zone of abnormally high pressure close to
Darwin and another close to Tahiti. In a typical El Nino the pressure at
Tahiti drops below normal, and this isn't happening yet. The most remarkable
information from the June anomaly pressure map is the zone of lower than
normal pressure across the North Pacific tropics. This is leading to extra
convection and tropical activity, especially off the Mexican west coast;
latest feature there is tropical depression DOUGLAS.

The Southern Oscillation Index SOI measures the impact of an El Nino or La
Nina episode on the atmosphere. An El Nino episode indicates more heat than
normal within or emanating from the Eastern equatorial Pacific Ocean EEP. We
have known for a few months now that extra heat is being stored in the EEP
mainly beneath the surface. During the past week the SOI has slipped into
negative territory, indicating that there may be a trend towards an El Nino
episode starting in the atmosphere.

TROPICAL TOPICS
Hurricane ARTHUR formed in the past week and managed to briefly sideswipe
North Carolina of the USA and cancel 4 July celebrations for many.

The weekly rain maps for the past fortnight show weather drying out over
Brazil for the World Cup, a burst of tropical convection just to east of
Philippines (Typhoon NEOGURI is likely to travel from there to Japan for
9/10/11 July) and Monsoon rain for Bangladesh. There has also been a strange
tropical depression in the South Indian Ocean (near 9S 83E).

WEATHER ZONES
SPCZ= South Pacific Convergence Zone
A weak convergence zone is expected to travel from Vanuatu on Monday to Fiji
on Wednesday and is likely to weaken. Otherwise the tropics in the South
pacific is likely to be quiet this week.

STR= Sub-tropical Ridge
The STR is weak and north of its normal position at present. There are some
large highs on the weather map but these seem to be related to jet streams
near 60S

Departing from NZ to the tropics
The subtropical jet stream emanating from Australia is north of normal, and
this is allowing a large upper trough to encircle the northern Tasman Sea,
allowing a surface low to form near Norfolk island on Monday and then deepen
a lot as it moves South until it finally weakens west of Taranaki on
Thursday. This is the low that has caught and is delaying Scott Donaldson,
and this is a typical winter weather pattern for NZ.
Associated front with heavy rain should cross Northland on Tuesday and
Wednesday, preceded by strong NE winds and followed by showery NW winds.
SO wait until Friday or Saturday before departure.

Departing westwards from Tahiti:
A trough and accompanying low is expected to travel for midway between Tonga
and NZ on Wednesday onto the Southern Cooks by around Friday UTC/Thursday
local. Avoid.
Also note that is not really a tropical feature, rather it is a feature in
the mid-latitudes, south of the STR, so is likely to be followed by SW winds
and swells.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
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.
My website is at metbob.com  Feedback to bob@metbob.com To unsubscribe,
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