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

28 March 2010

BOBGRAM issued 28 March 2010

WEATHERGRAM
YOTREPS
Issued 28 Mar 2010
Bob McDavitt's ideas for sailing around the South Pacific.
Corrected edition
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.

GALAPAGOS TO MARQUESAS Welcome to those of the new Puddle jump crowd
contemplating this voyage. Nothing much to report at this stage, all
looks quiet. Best east going current seems to be along around 30
minutes North latitude, but this may change.

TROPICS
It is looking to be another settled week in the tropical South West
Pacific. The next convective phase of the Madden Julian Oscillation is
not expected here until first or second week of April. There is some
bubbling activity over Northern Australia and Tropical depression
TWENTY-TWO is in the western side of Gulf of Carpentaria. Models differ
as its likely path, and currently it is most likely to go SW inland in a
few days. If it looks as though it may earn a name and make land fall
in southwest of the Gulf over Easter. If this system goes offshore and
towards the middle of the Gulf it will feed-and-grow on the warm seas,
and earn a name a cyclone. Even so it is then likely to make land fall
late in the week over southwest of the Gulf and then it'll starve and
die quickly.

South Pacific Convergence zone is still going through its re-build after
the cyclones of mid -March. It is currently mainly along 20S, feeding
off the subtropical Jetstream, with occasional burst further north (one
of these bursts is crossing Vanua Levu today/Sunday). Also there is
another zone building between 10 and 17S from around Northern Cooks to
French Polynesia. A trough is likely to develop on the SPCZ between New
Caledonia and Fiji around 31 march ad this should intensity into a LOW
as it moves south just west of the date line from Thu 1 April to do a
loop and end up east of the North Island on Mon 5 April ---
There's lots of convection in the Intertropical Convergence zone just
north of the Equator across most of the Pacific, and extending towards
the equator at times around Tarawa.

Next development to watch is a likely LOW developing in the North Coral
Sea. Models differ, and this area isn't really expected to bubble up
until after Easter, but it is worth watching this week.

SUBTROPICAL RIDGE:
HIGH cell is moving to east of the South Island tonight is expected to
build to over 1040hPa over Chathams on Monday. This high has brought a
wave of warm air from Australia to New Zealand and this warmth should
hang around all week.

Next HIGH , suitably shaped like an Easter Egg, is expected to cross
Aussie high around 1 April, to be south of Tasmania on 2-4 April, and
then may stall over NZ and gradually shift from Southland to Northland
from 5 to 8 April These highs are shepherding the lows around them ,
keeping rain away (from where it is wanted). This pattern is expected
to change during April.

TASMAN/NZ
Between the Highs there are some mediocre fronts this week. One is
likely to be attached to a LOW moving southeast over Southland on
Tuesday and Wednesday, preceded by a strong NW flow. This front should
stall and fade over central NZ on Thursday /Friday.

Another cold front, the herald of the Easter egg High, is likely from
southern ocean onto South Island on Friday and North Island on Saturday
- where it gets absorbed into the circulation of the LOW coming from
the north. Sometimes this can be a recipe for rapid intensification,
but this time it seems that the North Island mountains may block the
cold air that follows this front from circulating into the Low's moist
heart--- some heavy rain for eastern North Island, but not the full
works this time.

So, with fronts over NZ, an outgoing High, and a Low coming in to
northeast, it is Easter (south) easterlies for the traditional Auckland
to Tauranga Yacht race, and a spirited offshore wind to start the SOLO
TRANS-TASMAN CHALLENGE 2010 New Plymouth to Mooloolaba on Easter Sunday.
In New Zealand we are celebrating Easter this year with a 25 hour day
(it coincides with turning the clock back from NZDT to NZST).

May the Easter message bring all humans joy and a sense of purpose.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

BOBGRAM7 addendum 29 March 2010

Whoops. In my last weathergram I mentioned that the change on Sun 4
April from NZDT to NZST would give us a 23 hour day. Of course I meant
a 25 hour day... An extra hour to sleep in or to search for Easter eggs
:)

Bob McDavitt

27 March 2010

BOBGRAM7 issued 28 March 2010

WEATHERGRAM
YOTREPS
Issued 28 Mar 2010
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.

GALAPAGOS TO MARQUESAS Welcome to those of the new Puddle jump crowd
contemplating this voyage. Nothing much to report at this stage, all
looks quiet. Best east going current seems to be along around 30
minutes North latitude, but this may change.

TROPICS
It is looking to be another settled week in the tropical South West
Pacific. The next convective phase of the Madden Julian Oscillation is
not expected here until first or second week of April. There is some
bubbling activity over Northern Australia and Tropical depression
TWENTY-TWO is in the western side of Gulf of Carpentaria. Models differ
as its likely path, and currently it is most likely to go SW inland in a
few days. If it looks as though it may earn a name and make land fall
in southwest of the Gulf over Easter. If this system goes offshore and
towards the middle of the Gulf it will feed-and-grow on the warm seas,
and earn a name a cyclone. Even so it is then likely to make land fall
late in the week over southwest of the Gulf and then it'll starve and
die quickly.

South Pacific Convergence zone is still going through its re-build after
the cyclones of mid -March. It is currently mainly along 20S, feeding
off the subtropical Jetstream, with occasional burst further north (one
of these bursts is crossing Vanua Levu today/Sunday). Also there is
another zone building between 10 and 17S from around Northern Cooks to
French Polynesia. A trough is likely to develop on the SPCZ between New
Caledonia and Fiji around 31 march ad this should intensity into a LOW
as it moves south just west of the date line from Thu 1 April to do a
loop and end up east of the North Island on Mon 5 April --- There's lots
of convection in the Intertropical Convergence zone just north of the
Equator across most of the Pacific, and extending towards the equator at
times around Tarawa.

Next development to watch is a likely LOW developing in the North Coral
Sea. Models differ, and this area isn't really expected to bubble up
until after Easter, but it is worth watching this week.

SUBTROPICAL RIDGE:
HIGH cell is moving to east of the South Island tonight is expected to
build to over 1040hPa over Chathams on Monday. This high has brought a
wave of warm air from Australia to New Zealand and this warmth should
hang around all week.

Next HIGH , suitably shaped like an Easter Egg, is expected to cross
Aussie high around 1 April, to be south of Tasmania on 2-4 April, and
then may stall over NZ and gradually shift from Southland to Northland
from 5 to 8 April These highs are shepherding the lows around them ,
keeping rain away (from where it is wanted). This pattern is expected
to change during April.

TASMAN/NZ
Between the Highs there are some mediocre fronts this week. One is
likely to be attached to a LOW moving southeast over Southland on
Tuesday and Wednesday, preceded by a strong NW flow. This front should
stall and fade over central NZ on Thursday /Friday.

Another cold front, the herald of the Easter egg High, is likely from
southern ocean onto South Island on Friday and North Island on Saturday
- where it gets absorbed into the circulation of the LOW coming from
the north. Sometimes this can be a recipe for rapid intensification,
but this time it seems that the North Island mountains may block the
cold air that follows this front from circulating into the Low's moist
heart--- some heavy rain for eastern North Island, but not the full
works this time.

So, with fronts over NZ, an outgoing High, and a Low coming in to
northeast, it is Easter (south) easterlies for the traditional Auckland
to Tauranga Yacht race, and a spirited offshore wind to start the SOLO
TRANS-TASMAN CHALLENGE 2010 New Plymouth to Mooloolaba on Easter Sunday.
In New Zealand we are celebrating Easter this year with a 23 hour day
(it coincides with turning the clock back from NZDT to NZST).

May the Easter message bring all humans joy and a sense of purpose.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

21 March 2010

BOBGRAM7 issued 22 March 2010

WEATHERGRAM
YOTREPS
Issued 22 Mar 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

I am a day later than usual this week, since I spend 9 hours driving
back to Auckland yesterday and decided to rest in the evening.

TROPICS
Now that TOMAS and ULUI have taken away most of the convective energy
build-up in the South Pacific, it looks as though' we may be in for a
reasonable quiet period now. The South pacific Convergence Zone SPCZ
today stretches from Vanuatu to Fiji/Southern Tonga to south end of
Southern Cooks. This zone is expected to drift north and weaken this
week. Also, the forecast is for a build-up of convection in the central
Coral Sea, and maybe a low or a trough of light winds near New Caledonia
around this weekend from Friday 26 to Sunday 28 March.

We had the equinox last Sunday, and as the sun is now overhead in the
Northern Hemisphere, it is interesting that a tropical depression has
developed in the NW Pacific. This is expected to weaken to east of
Philippines by Friday 27 March.

SUBTROPICAL RIDGE:
HIGH cell is forecast to cross the Southern Bight on 23 March (World
Meteorological day) and then cross the Tasman Sea/Northland area on 25
to 27 March keeping the rain away. There will be an enhanced zone of
trade winds along 25S. This zone will extend eastwards all the way to
the date line as the High cell moves east. More fetch for more swell
for the Brissy coast.

The next HIGH cell is likely to take a more southern route, crossing
Tasmania on Friday 26 March and then the South Island on Sunday 28
March, producing a squash zone of onshore easterly winds onto the
southern North Island. Avoid.

TASMAN/NZ
Deep Southern ocean Low wandered close to Fiordland earlier today so
that its front was intense with 75 knot gusts and well over 100mm rain
on the Southern Alps. The wind helped delay the cricket in Wellington.
Front will weaken as it crosses the rest of NZ on Tuesday.

Another deep Southern Ocean Low is likely to wander north close to Otago
on Thursday. Its front should cross NZ on Wednesday preceded by strong
NW winds and heavy alpine rain and followed by an unsettled westerly
flow.

Then, on Friday we are forecasting the front that will lead in a HIGH
cell. It, too, will likely be heralded by intense Northwest wind and
rain over south end of NZ, but this time it will be followed by
southerlies and clearing weather - and not as cold as the last one
(which gave many inland areas a frosty start to 18 March last week).

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

13 March 2010

BOBGRAM7 issued 14 March 2010

WEATHERGRAM
YOTREPS
Issued 14 Mar 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.

TROPICS
It's another busy week of weather in paradise this week.
TC TOMAS is now 975hPa near and west of Futuna, heading SSW and should
swing more to the south so that its centre crosses close to Udu point
east side of Vanua Levu and across the Lau group. It is a large cyclone
with a wide ring of gales. It should weak and accelerate as it leaves
the tropics passing by the Kermadecs on wed 17 March and then off to the
southeast.
TC ULUI is very compact - smaller in size than TOMAS, but more intense,
central pressure 945 hPa today and taking an unusual track to the
northwest so that it will bother some of the southern Solomon Islands
tonight and on Monday. Then it should wander west and then SW so that
it gets into the central Coral Sea by Wednesday and Thursday and feed
off its warmth and grow according. Then is should swing south getting
close to west-of-New Caledonia on Friday 19 March and as close as it'll
get to Queensland coast on Sat sun 20/21 March... EC model then takes
it towards Northland early next week around 22 March... too far away to
be sure yet so double check and plan accordingly.
There is a squash zone on the south side of ULUI, between it and the
subtropical ridge over southern Australia. This squash zone will be
generating strong winds and heavy swells that will peak off Brisbane
late in the week . Avoid.

SUBTROPICAL RIDGE:
HIGH cell lies south of French Polynesia PF and should slowly wander to
east this week, allowing TOMAS to track south along its western flank.
This High should maintain trade winds over PF and east to northeast flow
over the Cooks and Samoa.

HIGH 1035+ to east of Tasmania today should fade away as it noses to the
northeast so that it is a drawn-out ridge of just over 1020 hPa over
Northland by Friday 19 March. This ridge is expected to pull off to the
east of NZ over the weekend - following the path of the remains of TOMAS
from the south leaving a centre nose itself eastwards across.

TASMAN/NZ
We had a squally southerly over central NZ on Fri 12 March, as mentioned
in last weathergram. 60 to 70 knot onset in Wellington; and the roaring
40s have been gale force over southern NZ past few days, keeping the
oyster boast in harbour.

Next cold front and southerly change is expected to rip north across NZ
on Tue 16 Wed 17 March, preceded by SW and followed by gusty SE winds
then followed over the North island by lighter winds of a ridge on 18
and 19 March. The South island should get further weaker southerly
fronts on Thursday, Saturday and Sunday. SO it's not settled.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

06 March 2010

BOBGRAM7 issued 7 March 2010

WEATHERGRAM
YOTREPS
Issued 07 Mar 2010
Bob McDavitt's ideas for sailing around the South Pacific.

Disclaimer: Weather is a mix of pattern and chaos; these ideas come from
the patterned world of weather maps, so please fine-tune to your place.
Dates are in UTC unless otherwise stated.


TROPICS
South pacific Convergence Zone SPCZ is active along 10S and has a zone
of equatorial winds from west or northwest on its northern side
extending from Solomons to Tarawa. No good for fishing, diving or
mooring.

This is likely to culminate in a new Tropical system forming somewhere
near Tokelau. Computer output all differs at this stage as to timing,
but most likely track of this system would be somewhat to the southwest
into the Wallis/Futuna/Rotuma area by around Thu Fri 11/12 Mar and then
about or west of Fiji over weekend of 13/14 March or maybe early next
week 15/16 March. Double check with updates and plan accordingly.

SUBTROPICS/TASMAN

The subtropical ridge is still well south of its normal latitude and the
high cells are getting further apart, allowing the troughs in-between to
bring doses of northerly then southerly winds to the mid latitudes and
almost into the tropics.

That Low in the subtropics between Raoul and Chatham Islands or just
east of the NZ North Island today should fade away near Chathams by
Tuesday and has meant that its partnering high cell has had to skirt
around it along 50S.

This has weakened the subtropical ridge and upset the normal westerly
flow in the southern ocean a bit and so the next trough rolling in from
the west is likely to turn into something of a polar blast as a
consequence. Well, OK, maybe not a true polar blast but one that will
allow the cold air near 55S to get to something like 35S. Cold
southerlies/southwesterlies and huge swells are likely to hit Tasmania
on Tuesday 9 Mar and then follow an active front onto New Zealand on
Thu/Fri 11/12 Mar and Chathams on Fri 12 March.

So forecast for Auckland Boat Show is for a showery SW change around
about late Thursday, clearing and easing for the weekend. There may
well be some mountain snow on southern facing hills of South Island
Thu/Friday, but soil temperatures should be warm enough to melt it on
Saturday.

This cold blast just doesn't seem to have the right timing to get
into the subtropics. If it did, that would cause a rapidly deepening
low. Maybe next time.

Another factor feeding this 55-to-35S blast is the next HIGH which is
likely to expand to 1036 over Tasmania on Friday, shovelling the air
ahead of it northeast wards. This high should move over central NZ
around the middle of next week, good for Saint Paddy day revelry.

The terms used are more fully explained in the METSERVICE Yacht Pack.
More info at http://weathergram.blogspot.com
Feedback to bob.mcdavitt@metservice.com

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