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

03 August 2014

BobBlog issued 3 Aug 2014

WEATHERGRAM
YOTREPS
Issued 3 August 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.

Negative storm surge
A few weeks ago I shared on my blog that I was having problems explaining
the consistent negative storm surge at Green Island. I have been since
informed by NIWA that the gauge was damaged and the new pipe ended up being
shorter than the previous one, so was reading lower than before.
An offset has been applied and readings are OK now.

TROPICAL TOPICS
More action this week
Tropical Storm BERTHA in North Atlantic
ISELLE is expected to weaken as it approaches Hawaii.
HALONG is approaching southern Japan.
And NAKRI is visiting Korea.
The weekly rain maps for the past fortnight show a northward shift in the
tropical convergence zone over the NW Pacific. Not much change in the South
Pacific.

WEATHER ZONES
SPCZ= South Pacific Convergence Zone
The SPCZ has been steady in position for a week or so, and part of it may
spread south into Coral Sea or onto Fiji by the end of this week. A Low is
expected to form near 25S 140W by Monday (Sunday local) and this feature
should go SE this week.

STR= Sub-tropical Ridge
There is a High moving east well to the east of NZ along 30 to 35S this week
on Monday. It has a squash zone of enhanced trade winds on its northern
side around 10 to 15S which has recently been bothering Fiji and Tonga and
is expected to bother Samoa on Monday and Southern Cooks on Tuesday (UTC).
The next HIGH is expected to depart the Aussie bight on Wednesday and travel
east along 30/35S reaching northern NZ on Sunday 10.

Departing westwards from Tahiti:
OK to depart and travel west, but be mindful that there are some strong SE
winds around until Tuesday UTC.

Departing from NZ to the tropics
A low is expected to cross central North Island on Monday, bringing a
squally change to SW winds to Northland in the afternoon: that could be a
boost for departures going north- or maybe some might prefer the quieter
winds on Tuesday. A Monday departure should get a better go (than a Tuesday
departure) at crossing the light wind zone of the
subtropical ridge near 30S. After Friday winds are likely to get too
light for a good departure.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram text only (and translator) is at weathergram.blogspot.co.nz
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