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

25 May 2014

BobBlog

WEATHERGRAM
YOTREPS
Issued 25 May 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 has had made good progress in the past week kayaking across
the Tasman Sea. Tonight he is in 4 to 5 metres swells and 20 knot winds from
the SW, and managing to make way to the southeast.

The Ocean: The warmer the sea the quicker it evaporates, tossing water
vapour into the air, where is rises and cools into cloud. The equatorial
Pacific region hosts the warmest sea on the planet. Thus its sea surface
temperatures SST is a factor in the running of planetary weather engine.
An index for this is NINO3.4 and its abnormalities tend to influence changes
in clouds along the equator and thus tweak the latitude zones of weather
around the planet. Recently a lot of extra heat has been stored in the upper
depths of the equatorial Pacific Ocean and some of this is now reaching the
surface near the Galapagos.

TROPICAL TOPICS
The new hurricane season in northern hemisphere is meant to start at the end
of this month and already HURRICANE AMANDA has started off the west coast of
Mexico:

WEATHER ZONES
SPCZ= South Pacific Convergence Zone
South end of SPCZ is expected to visit Fiji on Monday 26 May UTC, Tonga on
Monday/Tuesday, Niue on Wednesday and Southern Cooks on Thursday/Friday UTC.
Another part of the SPCZ is likely to spread south onto Tonga again around
Sat 31 May UTC.

STR= Sub-tropical Ridge
The STR is north of its normal position for this time of the year in
Australia, and mainly at its normal position between 30 and 35S across the
Pacific.
Tonight a high has budded off from the Antarctic ice shelf and travelled NE
into the South Tasman Sea/, shovelling ice-chilled SSW wind flow onto
Southern NZ. This cold high is expected to travel NE cross the Tasman Sea on
Monday and northern NZ on Tuesday and then travel east along 30/35S into the
Pacific.
The next HIGH is expected to move off Australian coast into central Tasman
on weekend of 31 May/1 June

Departing from NZ to the tropics
A cold southerly/SW flow over northern NZ on Monday is good for going north,
Light winds over northern NZ on Tuesday with passing HIGH, not so good for
sailing.
Then a large and intense trough is expected to approach North Island on
Wednesday, with increasing NW winds, and cross the Island on Thursday with a
period of squally showers. Not good for departure.
The decreasing SW flow on Friday may offer a good weather pattern for
departure  but such a departure might encounter a new trough over the
Tongan area the following week, too far away to tell at this stage. A Friday
departure might work ok.

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, send
a reply email saying unsubscribe.

18 May 2014

BobBlog 18/19 May 2014

WEATHERGRAM
YOTREPS
Issued 18/19 May 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.

Apologies for late posting today; I was delivering a weather seminar and it
took a while to clear my inbox this evening.
First: A plea for your help,
I have an adventurer kayaker who is raising funds for the ASTHMA foundation
by paddling the Tasman, Australia to NZ. Scott Donaldson had to stop at Lord
Howe this week (see photo) to replace his desalination equipment, and is now
on his way again. I think if we all donate $2 via
http://www.doubleditch.co.nz/donate (click: donate any amount icon) then
this will boost his spirits tremendously. He has already achieved a record
as being the only human who has, so far as we know, kayaked from Australia
to Lord Howe Island!
You can learn more about his exploits at:
http://www.maxyourmedia.com/radiosport/ScottDonaldson9May14.3gp
Judge for yourself if he has earned a $2 donation. (cheaper than the cost of
a cuppa, but if you all do it then thats $1000 to ASTHMA).

SOI. The Southern Oscillation Index SOI sums up the weather pattern over the
South Pacific as one number. It is based on the standardized difference in
the barometer readings between Tahiti and Darwin.
SOI (30 day running mean) has switched from pink to blue recently and is now
near zero

TROPICAL TOPICS
Still in the strange inter-seasonal zone with no cyclones around. Last week
looked normal.

WEATHER ZONES
Galapagos to Marquesas
No problems with any convergence zones. To get the best benefit of the
available current go for 3:30S 98W then 6S124W then direct to Marquesas.

SPCZ= South Pacific Convergence Zone
Once the Low that is tonight over Tonga goes off to the SE/SSE over the next
few days, the SPCZ is only likely to be noticeable from Papua New Guinea to
Samoa. By next weekend we likely to have just trade winds across the South
Pacific.

STR= Sub-tropical Ridge
The STR is north of its normal position for this time of the year, possibly
a hint that we may be moving into an El Nino. It is also reasonably strong,
with High cells expected to make it across northern NZ on Tuesday/Wednesday,
and along 30S to north of NZ on Fri/Sat 23/24 May.

Minerva
My reporters tell me that there are 26 Yachts at Minerva tonight. I wonder
what the record is.
They have had strong winds since Saturday afternoon, and been on anchor
watch all last night, but no dragging. There is a squash zone between the
High in the Tasman and the Low over Tonga --- this was referred to in my
last weeks weathergram with an AVOID. It was 30 gust 40 knots there last
night, still 25 gust 35 knots today and tonight. Forecast is for wind to
ease on Monday but may take till Thursday for waves to ease back to the
average of 2 metres.
This squash zone is covered by a gale warning in the SUBTROPIC area covered
by MetService.

Departing from NZ to the tropics
Light winds over northern NZ on Monday/Tuesday with passing HIGH, Disturbed
westerly flow is spreading northwards this week and should reach northern NZ
with a passing front on Wednesday. Another front over northern NZ on
Saturday night/Sunday, preceded by strengthening NW winds.

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,
send a reply email saying unsubscribe.

11 May 2014

Bob's Blog

WEATHERGRAM
YOTREPS
Issued 11 May 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.

SOI. The Southern Oscillation Index SOI sums up the weather pattern over the
South Pacific as one number. It is based on the standardized difference in
the barometer readings between Tahiti and Darwin.
SOI (30 day running mean) was in the pink and below minus 10 in the
farmonlineweather.com graph for much of April but started May in the blue
and is now falling again.

The World Meteorological Organization now says that a recent weakening of
trade winds has significantly warmed the sub-surface waters of the central
Pacific. This warm anomaly is now rising to the surface. When this warmth
reaches the surface we shall have an El Nino episode, and that maybe be
within a month or two. The amount of extra heat currently store in the
tropical Pacific has been measured to be on a par with the amount that gave
us the last big El Nino in 1997/8. We shall see/sea.

TROPICAL TOPICS
In the past week there has been some intense pre-monsoonal rain over Sri
Lanka and southern India. An intensive convergence zone moved over Sri Lanka
last Monday. A squally shower formed a waterspout over a shallow river,
resulting in a rain of fish on nearby fields. See http://www.
earthweek.com/2014/ew140509/ew140509h.html for more details.

No tropical cyclones on the planet for the past two weeks, we are in that
interesting hiatus of changing seasons. During the past week the ITCZ has
been very active off the west coast of Central America. Later this week a
tropical low is expected to form near 9S 90W around Wednesday and this
should then travel out to the west and northwest.

WEATHER ZONES
Galapagos to Marquesas
No problems with any convergence zones. To get the best benefit of the
available current go for 3S96W then 6S121W then direct to Marquesas.

SPCZ South Pacific Convergence Zone
This is now weak and about to spend a week or so at the north end if its
range.
A small trough in the trade in belt is expected to form over the Loyalty
group between New Caledonia and Vanuatu on Thursday and then move SE
crossing the Minerva area on Friday night. This system may carry a zone of
strong easterly wind and near 3 metre swells on its south side, a small
squash zone. AVOID. This feature may then stall and hover a few days and
deepen into a low around Tuesday 20 May near the Kermadecs. Too far away to
tell.
Some of the more erratic weather models (see last week weathergram for more
explanation) are making more of this trough than the more reliable weather
models.

STR Sub-tropical Ridge
High in the Tasman Sea tonight should fade away as it crosses northern NZ on
Monday, and then redevelop as it travels east along 30 to 40S.
High moving off New South Wales on Monday is expected to take its time
crossing the Tasman Sea this week and then cross NZ on Friday.

Departing from NZ to the tropics
A trough is expected to cross NZ on Tuesday (stay put) followed by a showery
W/SW flow over northern NZ on Wednesday (might be OK for departure).
This should ease and turn more southerly on Thursday (OK for departure), and
lighter more variable winds on Friday.
There may be another trough approaching NZ over this coming weekend.

Over the past week and into the next week, there has been a noticeable
increase in the number of westerly isobars in the Southern Oceanthe lows at
60S are now regularly reaching 980hPa.

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  To unsubscribe, send a reply email saying
unsubscribe. Feedback to bob@metbob.com

04 May 2014

Bob's Blog issued 4 May 2014

WEATHERGRAM
YOTREPS
Issued 04 May 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.

SOI. The Southern Oscillation Index SOI sums up the weather pattern over
the South Pacific as one number. It is based on the standardized difference
in the barometer readings between Tahiti and Darwin.
SOI (30 day running mean) was in the pink (below minus 10 in the
farmonlineweather.com graph for much of April but is now blue again.

TROPICAL TOPICS
May 1st marked the nominal end to the Southern Hemisphere cyclone season,
and the beginning of a period where cruising sailors in NZ examine the
weather maps closely searching for a good weather pattern for departure to
the tropics. In my blog last week I picked Wednesday 30 April as being the
best day last week for a departure (to Fiji/Tonga, not so good for getting
to New Caledonia or Vanuatu.

SO here are a few web sites to help examine the possible weather over the
next week or more. Possibly the most reliable weather model around at
present is the ECMWF. Especially in the tropics. This can be found at
http://bit.ly/1iM8kil

Weatheronline is the only website I have come across where I can quickly
compare the ECMWF with the world #2 model UKMO and also with the more
erratic GFS and several other models at http://bit.ly/1fHqGAt. This is a
good site to check when the GFS model (as seen at
http://www.metvuw.com/forecast/forecast.php?type=rain&region=swp&noofdays=7
)
is having one of its flights of fancies.

The PWG regional model (predictwind.com) starts with the GFS,
and the MetService regional model ( http://bit.ly/7daywx ) usually starts
with the UKMO.
A nice interface to loop the GFS ensemble model is offered by
Tropicaltidbits.com at http://bit.ly/1mrigQP

WEATHER ZONES
Panama to Galapagos: After 1 May the NE wind bursts that are good for this
voyage become further apart. Also the SW winds on the route are likely to
become more common. Tropical Lows are now likely to form on the northern
side of the ITCZ over the sea, but these are unlikely to affect
this passage. SO it may be best, if still in Panama or Las Perlas, to
motor off during the next few days. You are likely to experience light
winds for the first half of the voyage and then Southerly winds, which may
be used to sail the second half of the voyage to Galapagos.

Galapagos to Marquesas
There is a convergence zone within 100 miles of a line from 2N 97W to 2N
105W at present. If departing in next few days go SW to 4South and then go
direct to divert around these nasty squalls.

SPCZ= South Pacific Convergence Zone
This is about to spend a week or so more active to east of 180 than in the
west. It is active from Solomons to Tokelau and then more active in a line
stretching across the Tuamotu group.
If you are heading for Tahiti this week then you need to take this into
account.
Also note that there is a subtropical Low near 30S this week, then travel
from 170W 50 150W and then going SE. If you are on a voyage to Tahiti this
week the GO CLOCKWISE around this low.

STR= Sub-tropical Ridge
The STR has been weak over the Tasman Sea/NZ area last week and this is
likely to be the case this week as well. There is a HIGH in the Australian
Bight that is likely to cross Tasmania on Thursday and then follow the STR
across northern NZ early next week.

Departing from NZ to the tropics
A front is expected to cross Northland on Monday night followed by moderate
westerly flow on TUESDAY. This makes TUESDAY an OK day for departing off to
the north.
A squally trough should cross Northland on Wednesday and Thursday and then a
strong SW change on Friday, with swells from the Southern Ocean reaching as
far as 28S. Also on Friday a tropical trough is likely to travel across the
New Caledonia region, but this is expected to weaken as it travels further
east over the weekend. These features may bug a Tuesday departure but not
by much.

On SATURDAY there is an easing SW flow over Northland followed by that HIGH
crossing the Tasman Sea at around 1024 hPa intensity. This should offer a
good voyage off to the north as well. Still too far way to fully comment of
this voyage, but its start does look good at this stage.

See my yotpak at boatbooks.co.nz/weather.html for terms used.
Weathergram with graphics is at metbob.wordpress.com, click FOLLOW at bottom
right to subscribe. Weathergram text only (and translator) is at
weathergram.blogspot.co.nz My website is at metbob.com - To unsubscribe,
send a reply email saying unsubscribe. Feedback to bob@metbob.com

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