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

29 June 2014

BobBlog issued 29 June 2014

WEATHERGRAM
YOTREPS
Issued 29 June 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.

Kiwis can brace for a real bit of winter on Wednesday and Thursday this
week. This isn't going to be southerly eggbeater but is expected to be a
polar outbreak, good for snow for the ski-fields, just in time for the
school term 2-week break from 4 July.
The polar vortex is the name given to that westerly spin of wind around
Antarctica, holding the cold in the south. Sometimes the vortex weakens and
that allows high cells to snap free from the ice shelf and travel to the
northeast, dislodging ice-chilled air and shovelling it northwardsthats
what I mean by a polar outbreak, NIWA use a parameter called the Southern
Annular Mode, or SAM, to measure the strength of the polar vortex. When this
dives suddenly negative the chances of a polar outbreak increase. Sometimes,
such as this week, the polar outbreak gets into the Tasman Sea. I don't have
any real time access to the SAM index, but a good proxy for it is the AAO or
Antarctic Oscillation, and its expected future trend is shown at

http://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/aao/new.a
ao_index_ensm.html

and this shows a sudden dive into the negative on 1 to 3 July, but not for
long.
SO by noon Wednesday most of the inland South Island is likely be have air
temperatures below zero, and in many places be wet enough to snow


TROPICAL TOPICS
There is a lot of convective activity this week off the west coast of
Mexico.
And there is still less than normal convective activity over India, Reports
are that the monsoon is over 40% deficient over much of central India.
All of this shift of convection is consistent with an observed warming of
the sea in the eastern equatorial Pacific Ocean as measured by the NINO3
index
NINO3.4 index measures the difference from normal of sea temperatures in the
EEP (eastern equatorial Ocean) and this has been on the rise in recent
weeks, but still hasn't swung the SOI index (in the atmosphere) towards El
Nino.

WEATHER ZONES
SPCZ= South Pacific Convergence Zone
This continues to intensify in the Coral Sea to Tokelau area and is expected
to drift south towards Vanuatu /Futuna and maybe New Caledonia on 5/6 July.
A weak convergence zone is likely to linger over the west end of French
Polynesia during Monday and Tuesday UTC.

STR= Sub-tropical Ridge
The STR is in its normal latitude position of 30 to 40S this week. One High
cell that was over northern NZ on Sunday is expected to travel east along
30S this week. The next high leaving Australia on Thursday is likely to be
weaker than its predecessor and diverted to 30S to north of NZ by Saturday 5
July.

Departing from NZ to the tropics
Large trough is crossing Tasman Sea and NZ over next few days, the first
front is expected to cross NZ on Monday, preceded by N /NE flow, and
followed by squally NW/W winds. Then the cold SW/S winds from the ice at 60S
are expected to spread across NZ on Wednesday and Thursday.
SO Friday looks to be the best weather pattern for departing Northland this
week.

Departing westwards from Tahiti:
There is a lingering weak convection zone around Papeete on Monday/Tuesday
UTC and another is expected around Sat/Sun 5/6 UTC and these zones weaken
the trades and may provide a few tropical squalls, Between these the weather
pattern is looking good to go.

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.

22 June 2014

BobBlog 22 June 2014

WEATHERGRAM
YOTREPS
Issued 22 June 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 is now 75% across, in his attempt to Kayak the Tasman Sea, and maybe
15 days away from New Plymouth. MetBob is helping this attempt with weather
information. Scott had an airdrop on Friday and that has increased his
costs, however he is raising funds for the Asthma Foundation. You can help
him by checking out http://doubleditch.co.
nz/donate

TROPICAL TOPICS
CRISTINA exploded into life on 12 June off the west coast of North
America, and HAGIBIS hit Guangdong (China) on 15 June.
The Indian Monsoon is still arriving late, and thus there has been a heat
wave ahead of it over north central India, with 371 heatstroke victims and
temperatures in Delhi reaching 45C for six days straight.
Tropical rain maps over the past two weeks show that the International
convergence zones is starting to expand. The South Pacific Convergence zone
is remaining closer than normal to the equator.
There has been some torrential rain in Natal at eastern end of Brazil,
intense enough to produce sinkholes and landslides. Apparently the rain in
Natal is not stopping the parties in the streets after the World Cup games.

WEATHER ZONES
SPCZ= South Pacific Convergence Zone
This is stronger than last week and slowly spreading south. It is likely to
trigger a trough that should develop as it crosses Fiji and Tonga on
Monday/Tuesday UTC and then deepen into a low over Southern Cooks on
Wednesday / Thursday UTC and then travel off to the SE.

STR= Sub-tropical Ridge
The STR is in its normal latitude position of 30 to 40S this week. One High
cell over NZ on Monday is expected to travel east along 40S, and another
High Cell travelling across central Australia on Wednesday is expected to
travel across northern NZ on Saturday/ Sunday 28/29 June UTC.

Departing from NZ to the tropics
Large trough is crossing Tasman Sea and NZ over next few days, the fronts
are expected to cross NZ on Wednesday/Thursday local, preceded by N /NE
flow, accompanied by rain and followed by W winds. These winds should back
to showery SW winds for Friday and Saturday.
SO if departing from Northland for the tropics this week better to wait
until late Thursday for departure.

Departing westwards from Tahiti:
If going just as far as Southern Cooks then it may be OK for a Sunday local
departure.
It is a good idea to wait for that trough to reach and move off Tahiti 
from Saturday 28 June local.

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.

16 June 2014

BobBlog issued 16 June 2014

WEATHERGRAM
YOTREPS
Issued 16 June 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.

Todays edition is a day delayed (I was out for dinner last night :)

There was a full moon on Friday 13th and a perigee of the moon on Sun 15th,
so that spring tides this month are larger than normal. Data of the actual
sea level for Whitianga (on the Coromandel/east coast of the North Island)
shows a storm surge (SS) of 0.6 metres in the NE gale last Tuesday night
(morning of 11th) and this has eased to 0.2 metres since then. Just as well
the air pressure has been around normal in the past week here so that there
was little to no Inverse Barometer (IB) affect.
This Storm surge (SS) and Inverse Barometer (IB) effect on sea level data at
Whitianga for the past week can be seen at http://www.niwa.co.nz/our-
science/coasts/tools-and-resources/sea-levels/whitianga-wharf


TROPICAL TOPICS
There is a tropical depression off the North America coast (CRISTINA) but
nothing much to report.
The Indian Monsoon was about a week behind schedule this time last week, and
is now about 5 days behind schedule.
Tropical rain maps over the past two weeks show that the convergence zones
are starting to get closer than normal to the equatorthere is a huge bulge
of monsoon rain, but it is lagging to the SW of India.
Brazil is remaining mainly dry (and warm) for the Football/Soccer World Cup.
For the average statistics of rain and temperature for Brazil cities during
the cup try reading http://fivethirtyeight.com/features/we-have-a-
weather-forecast-for-every-world-cup-match-even-the-ones-a-month-away/


WEATHER ZONES
SPCZ= South Pacific Convergence Zone
This continues to be weak or non-existent over much of the South Pacificand
is hugging close to the equator north of Papua New Guinea and north of its
normal position.

STR= Sub-tropical Ridge
The STR has in the last week reverted to its normal latitude range between
30 and 40S. High that was over northern NZ over the weekend is travelling
east along 30S and has a zone of enhanced easterly winds along 10to15S in
the tropics.
Next HIGH is expected to moves from Australian mainland into the western
Tasman Sea on Thursday and then onwards to northern NZ this weekend,
followed quickly by another high over southern NZ on Sunday 22 June

Departing from NZ to the tropics
Large trough is crossing Tasman Sea and NZ over next few days, the cold
front is expected to get east of NZ by Tuesday, and then there are several
waves of showery SW wind changes.
After a brief lull on Wednesday, a very strong burst of S /SW winds is
expected on Thursday, bringing large swells to the east coast. After the
high crosses northern NZ on Friday/Saturday, a low is expected to form in
the Tasman Sea by Sunday 22 June bringing northerly winds to northern NZ.
SO Best day this week to depart northwards from Northland may be Wednesday,
but if you would like a spirited departure with plenty of offshore wind then
look at a Thursday departure. A Friday departure may end up getting caught
in the weekend High.

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.

08 June 2014

BobBlog issued 8 June 2014

WEATHERGRAM
YOTREPS
Issued 8 June 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.

D-day was 70 years ago this week, a good report of the weather forecasting
crucial to this turning point of WWII is at http://uk.
weather.com/story/news/d-day-weather-forecast-changed-history-20140605

It was a year ago this week that we got the final test message from SV NINA
in the mid Tasman Sea and since then nothing has been seen of the vessel and
its occupants.
Herald reporter Annan Leask has marked this occasion with this report
http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11264844
The Nina Mystery is now one year old, and the MH370 mystery is nearly 3
months old. We live in interesting times. Our hearts go out to the lost and
to their families, and we hope that some lessons are learnt from these
events. Pray, one minutes silence please.
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
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
Over the last few weeks we have had little if any in the way of
cyclones/hurricanes/typhoons around the planet.
The Indian Monsoon is starting to arrive over southern India, about a week
behind normal, leading to some very dry anomalies.

Tropical rain maps over the past two weeks shoe that the convergence zones
are starting to get closer than normal to the equatorand this is producing
a warm zone along 20S, including over Brazil where the Football World cup
starts on Thursday. This is typical El Nino.

WEATHER ZONES

SPCZ= South Pacific Convergence Zone
This has weakened and travelled north in the past week, and is hard to find
in the weather prog maps for the coming week. There is likely to be a
convergence zone for a few days associated with and on the south side of a
low in the Coral Sea, but this is expected to fade away by Thursday.

STR= Sub-tropical Ridge
The STR has in the last week deviated to well south of its normal position,
with the HIGH that is currently moving across Tasmania expected to travel SE
across south Tasman Sea to SE of NZ by Tuesday and then east
along 50S, with central pressure well over 1030. There are enhanced
easterly winds on the north side of this High, and they are expected to help
spin up several LOWS in the 30 to 40S latitudes in the South Pacific this
week, including two over the NZ area. Lots to avoid, and rather an
abnormal situation. It is what old-style meteorologists would call low
index.

Departing from NZ to the tropics
Very wet front travelling south across the North Island on Monday is likely
to stall over central NZ on Tuesday to Thursday. Winds over Northland
should ease by Wednesday and then be in an OK direction for departure, but
better check this forecast again on Monday the Low that is currently
stationed west of Taranaki is expected to go west and then fade, and this
may allow an secondary to form on the front and do a clockwise loop over or
just west of the North Island, getting deeper than the first low and causes
all sorts of local wind/rain complications. This secondary should clear off
on Friday 13th

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.

01 June 2014

BobBlog issued 1 June 2014

WEATHERGRAM
YOTREPS
Issued 01 June 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.

It is Queens Birthday weekend here in NZ, and this reminds me: It was twenty
years ago today that the Pacific Storm started. This summary of the weather
pattern for that event is taken from the Mariners Met Pack at
http://www.boatbooks.co.nz/weather.html#23104

a) On Thursday 2nd June 1994, conditions were almost perfect for the voyage
across the South Pacific from New Zealand to Tonga or Fiji. A high- pressure
area was stuck over New Zealand, with steady trade winds from the Kermadecs
to Tonga.

b) But on Friday 3rd, a tropical depression started forming between Vanuatu
and Fiji. It was NOT a tropical cyclone because it did not have the
symmetrical warm central core that characterizes such systems.

Only when this depression moved south out of the tropics did it deepen
rapidly. This is because it started entraining very cold air, which had been
brought all the way from 60: South by that high-pressure system over New
Zealand. When cold air meets warm air, the warm air is bumped upwards out of
the way. If, as in this case, the upper winds remove the rising air faster
than the lower winds can replace it, then the surface pressure in the
immediate area falls rapidly.

c) Central pressure dropped from 1001 hPa at 0000 UTC Friday 3rd (noon local
time) to 986 on Saturday 4th, making this system a meteorological BOMB.
Clockwise winds around the low centre accelerated to over 50 knots during
Saturday, creating a confused, tossing sea with steeply sloped waves.
Conditions near Raoul Island had turned from fair to foul within
24 hours.

d) The low pressure system reached its peak about 0600 UTC Sunday 5th June
(6pm local time) with central pressure about 978 hPa, generating a swell
judged by rescue aircraft to be 1014 m. A senior pilot of the New Zealand
Airforce No. 5 Squadron with 10,000 hours experience commented that he had
not seen anything like these wave conditions before.

>From Saturday to Monday, 16 yachts in trouble set off EPIRB beacons,
twenty-one people were rescued, but three lives and seven boats were lost.

The weather pattern for this years Queens Birthday weekend has some
similarities to what happened 20 years ago, but also some differences.

During Queens Birthday weekend this year we have a High 1030 in the
southern Tasman Sea (something like 20 years ago), but it is NOT blocked
and is free to travel to east of NZ along 40S. By Wednesday this High
should be east of NZ at around 45S, and central pressure over 1032. There
is an old saying amongst weather forecasters when it gets over1030 the
weather gets dirtyand indeed by Wednesday there should be a squash zone
of enhanced trade winds on the north side of this high, mainly along
around 30S between 170W and 180.

A main difference between this week and 20 years ago is the Low. 20 years
ago it formed in the tropics and deepened rapidly as it encountered cold
air when moving out of the tropics. This year we have had a Low form near
33S 178E, to NE of Northland, today, and this feature is expected to get
pushed off to the NE and weaken during Monday. The low that appears on
the Wednesday map above has come out of the tropics and is encountering
cold airbut this is happening south of the Southern Cooks and there is
little if any marine traffic in that area - anyone sailing from NZ to
Tahiti needs to try and avoid that low.

Once that high starts to move off to the east, and the pressure starts
falling between NZ and Vanuatu next weekend, it is likely that a trough
should deepen to a low in that area, forming a strong NE wind squash zone
between NZ and Fiji . This is likely to pose a challenge to the Sail Fiji
Race 2014 starting on Sat 7 June.

Scott Donaldson was making good progress but encountered a front and then
SE winds last week and these have knocked him into a backward loop. You
can track him or help his cause at http://doubleditch.co.nz/tracking.
I am hoping his progress will be better in the coming week with some
northerly winds as a Low forms off Sydney on Monday and then turns into a
trough that crosses the South Tasman Sea on Wednesday to Friday and then
reaches southern NZ on Saturday and Sunday, but stalls in the north
Tasman Sea.

TROPICAL TOPICS
Rain over the past week shows that the Indian monsoon is getting late and
that there is an increase in activity off the west coast of Mexico


SPCZ= South Pacific Convergence Zone
SPCZ is expected to stretch from Papua New Guinea to Samoa this week.

STR= Sub-tropical Ridge
The STR is strong and in its normal winter latitude across the interior
of Australia, south of its normal position over NZ, and then around
normal around 40S well to the east of NZ.
The next High coming off Australia on Sun 8 June is likely to be diverted
across Tasmania so that it moves into the far south Tasman Sea on Sunday
8 June, leaving room in the North Tasman Sea for a deepening Low.

Departing from NZ to the tropics
Squash zone of strong easterly winds is expected to form east of
Northland by Tuesday and then slowly drift north---a departure on Monday
may be able to escape this.
A trough is expected to form between NZ and Vanuatu by the end of the
week with a strong NE wind between NZ and Fiji.

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.

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