Translator

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

31 January 2009

BOBGRAM7 issued 2 Feb 2009

WEATHERGRAM
YOTREPS
Issued 2 FEB 2009
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 has been most active across Coral Sea
recently breeding ELLIE near Queensland coast. There has been another
branch of activity between Solomons and Rotuma/Wallis/Futuna, breeding
HETTIE which was briefly a TC last Thursday == all in line with last
week's Weathergram.

Further east there are scattered parts of SPCZ but generally East or
Northeast winds, anticyclonic conditions and barometers above 1008,
enjoy.

HETTIE formed as a sheared system, with upper winds too strong for it to
build much height in its central core, so wind and rain from it over
Tonga was yuck but not too bad. The remains of HETTIE are somewhat
stuck in a trough that is linked to the SPCZ and lies between Fiji and
Kermadecs.
EC, NOGAPS, GFS and ww3 are handling this area slightly differently-as
an amalgam my pick is that another low will take over near Kermadecs
around Thu 5 Feb and then track southeastwards-with an associated squash
zone of southeast winds brushing past the North Island on Waitangi Day
Friday.

As an historic note HETTIE was named on the anniversary of GENE - which
was the last named TC in the South Pacific. It's the first time in the
era of satellites that a whole calendar year has gone between names ...
the main reason for this was the lack of named cyclones last Feb March.
Anyway, now that this cyclone season is well underway, it is interesting
to see the SPCZ displaced so far to south and west, truly a LA NINA
calling the shots.

ELLIE is holding together well aloft in the Coral Sea and, at present,
is forecast to approach land north of Townsville on 9am Monday local
time. A LOW of some sort is expected to stay around in the Coral Sea
all week this week, hopefully sufficiently far away from land so it can
do what TCs do (take the extra energy out of the ocean and share it
about) without too much hassle. However I'm anticipating that the
squally northerly winds on its eastern side will be encompassing New
Caledonia /Loyalties/ and parts of Vanuatu by 8 or 9 Feb.

SUBTROPICAL RIDGE / NZ
The STR is visiting NZ this week, bringing hazy lazy summer weather,
good for holidaying, but no good at all for those fighting fires or
wanting rain.

HIGH crossing Tasman Sea/NZ on 2 and 3 Feb, followed by a brief
transition trough on 3 and 4 Feb and then another HIGH taking a more
southerly path on 5 Feb, going north on 6 Feb, and another transition
trough on 7 Feb and another HIGH getting east of South Island on 8 Feb,
then a more substantial trough crossing Tasmania on 8 Feb.

So the wind for the Louis Vuitton Pacific Series near Bean Rock in
Auckland goes up and down---strong SW on Sunday due to troughing, switch
to NE winds on Monday due to ridging, easterlies on Tuesday to Friday,
maybe increasing if a low sideswipes the North Island from Kermadecs
later in the week, and possible SW change on Saturday.

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

24 January 2009

BOBGRAM7 issued 25 Jan 2009

WEATHERGRAM
YOTREPS
Issued 25 JAN 2009
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.

We are now entering HIGH SUMMER... the southern hemisphere equivalent of
"the Dog Days' of a dawning Sirius that is associated with the hottest
time of the year. This year in Fiji, the return of the sun after two
drenching weeks has caused very humid conditions there indeed. NZ has a
superb example of a summer HIGH stalled over the North Island-- and thus
a westerly flow over the South Island --- all set to make this to be
likely to be the warmest week of the year for NZ.

TROPICS
The South Pacific Convergence Zone SPCZ is active in a zone from Tuvalu
to Samoa along with some westerly winds on its northern side. It has
dumped a lot of rain in a branch from Samoa to Southern Cooks over past
week, associated with a tropical depression. There was another wet
branch from Samoa to French Polynesia, and a weaker branch from Northern
Australia across the Coral Sea to Loyalty Islands.

Over Monday and Tuesday, there is a good chance that a low may form over
SPCZ and drift south over or just east of Tonga, fading back into a
trough from Wednesday 28 Jan. The main rain with this feature will be
on its eastern side as it travels south-it may well wander a bit to east
or west as well, so treat with respect.

Another Low may possibly form on SPCZ to North of Fiji - perhaps around
Rotuma - on or around Wed 28 Jan and then take a generally southwest
track across Vanuatu and onto New Caledonia around 2 Feb. Not sure on
this ... NOGAPS model seems to be overdoing these lows and EC model is
perhaps undergoing them for a change, so this is an amalgam of possible
proceedings. Next week/early in Feb I think (along with the EC model)
that the focus of the tropical lows will be the Coral Sea.

We are nearing the end of January and haven't had a cyclone named in the
South Pacific so far this season, but one of the lows mentioned in past
paragraph may become worthy enough.


SUBTROPICAL RIDGE
The HIGH stalled in the Tasman Sea / North Island area has already been
mentioned. There will be a High replacement on Tuesday (old high fades,
new High builds in South Tasman Sea behind a front that brings a cooling
and damp southerly change that will be welcomed by eastern NZ). The
New HIGH should be a BFH, a big fat high, building to 1030 hPa in
central Tasman Sea on Thursday and lasting there until another High
replacement occurs around Sat 31 Jan /Sun 1Feb.

There will be a well-defined squash zone of enhanced trade winds between
this Tasman HIGH and the low pressures in the Coral Sea. This squash
zone is expected to be strongest between New Caledonia and the
Queensland coast between 20 and 25S from Wednesday to Friday.

TASMAN SEA/NZ
The superb summer High scenario may well make this the sunniest and
warmest week of the year for much of the country (but several wet days
in Fiordland, and some isolated afternoon downpours where sea breezes
collide over hot hinterland along with the arrival of some cooler air
aloft as surface pressure drops.

Tuesday is the odd day out, with a cool damp southerly change affecting
east coast, probably reaching Canterbury near noon. SO, overall, it is
a welcoming 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

17 January 2009

BOBGRAM7 issued 18 Jan 2009

WEATHERGRAM
YOTREPS
Issued 18 JAN 2009
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
Some parts of Fiji measured over a metre of rain in the past fortnight.
The remains of this MJO event- a pulse of extra convection moving east
across the South Pacific-are visiting French Polynesia early this week
along with some wet northwesterly winds.

The South Pacific Convergence Zone now stretches in a broad area from
North Australia across the Coral Sea to Vanuatu (with a side branch over
the Solomons) and then to South of Fiji. This branch is weakening and
expected to stay put or drift south this week, with NE winds on its
northern side, slack winds in its middle and SE winds on its southern
side.

An eastern branch of the SPCZ stretches from near Tuvalu/Samoa, between
the Northern and Southern Cooks to southern French Polynesia. This
zone is active near French Polynesia and may develop a low pressure
system near Suwarrow/ Suvarov from Tues 20 UTC that may deepen and cross
Southern Cooks on Friday 23 UTC. If you are in this area get updates
and brace for wind/rain.

SUBTROPICAL RIDGE
A HIGH is forming in the Tasman Sea today ... it should move slowly
along 35S and cross the North Island/central NZ from Wednesday to
Saturday, with a zone of enhanced trade winds on its northern side
slowly covering most of the South Pacific between 20 and 30S. There
will be a squash zone between the subtropical ridge and that low which
is likely to be crossing the Rarotonga area on Friday 23 UTC. This
squash zone is likely to reach its peak near 30S 160W on Sat 24 Jan UTC.
Avoid.

TASMAN SEA/NZ
South to southwest flow over New Zealand should last until Tuesday.
Then, until Saturday, that HIGH is likely to dominate the North Island
with light winds and settled weather -- whilst a northwest flow is
likely over the South Island coming from the hot interior of Australia
(some of this wind will be redirected through Cook Strait). Fronts
embedded in this NW flow are likely to lap onto the south on Wednesday,
Friday and Sunday with the last of these followed by a cooler southerly
change on Sun/Mon 25/26 Jan.

PS: I've just noticed that someone's stolen my bike - it was locked
outside this office and now it's gone. So make extra sure your stuff is
safe this 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

10 January 2009

BOBGRAM7 issued 11 Jan 2009

WEATHERGRAM
YOTREPS
Issued 11 JAN 2009
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
Last week we saw the MJO arrive in the Coral Sea. The South Pacific
Convergence zone splayed itself outwards as a broad trough from mid
Coral Sea across Vanuatu to south of Fiji/Tonga.

On its northern side: west to northwest monsoonal winds were able to
make their way east all the way to Southern Cooks. Typically wet and
squally, they were boosted by the mountains of Fiji, making Fiji the
wettest part of the world last week -- flooding rivers, closing towns,
and causing evacuation and two drownings. Over half-a-metre of rain in
a week:
See
http://trmm.gsfc.nasa.gov/trmm_rain/Events/big_global_accumlation.gif

On the SPCZ's southern side there is a squash zone in the trade winds
mainly between 25 and 30S.

Along the SPCZ's trough line are a few lows sometimes with weak winds
near their centres - one visited Vila on Wednesday and is now moving
southeast towards the Kermadecs, and another formed just south of
Rarotonga and has deepened near 33S 165W and is being steered to the
southwest. Yes , the southwest. This low has gales, avoid.

This week the MJO is expected to fade, and the SPCZ should stay in much
the same place, but lows that form on it will move off to the south.
One Low is expected to start near Vanuatu on Tuesday then deepen just
south of Fiji of Wednesday and the go southeast, crossing southern Tonga
on Thursday, Niue Friday and to south of Southern Cooks next weekend
(all UTC). Another Low is likely to form off to the SW of Fiji on
Friday. It's the monsoonal west/northwest winds on the northern side of
these lows that need to be treated with respect.

Over Australia a Low should briefly blossom in the Gulf of Carpentaria
on Tues/wed and then fade away.

SUBTROPICAL RIDGE
The tropics seem to be at their wettest when the Subtropical ridge is at
its southernest. Last week we had a slow-moving high crossing NZ. NOT
this week. There is a HIGH moving quickly east off the South Island
today Sunday, and another is excepted to build in the Tasman Sea on
Monday/Tuesday-that will then shrink to northern Tasman Sea by Friday
and then zip like a flicked pip along 30S and past the dateline this
weekend. SO the Subtropical ridge is expected to reform near 30S by
this weekend and that should help the SPCZ to go north and weaken by
next week.

TASMAN SEA/NZ
AT first the South Island should enjoy light winds and settled weather
with a ridge, and for the North Island there is a southeasterly flow.
Part of that Low heading southwestwards may reach the dateline around
Thursday to east of the North Island, turning the winds over the North
Island more southerly. A block has formed in the upper air just east
of the dateline and that's why that Low (or part of it) is taking this
unusual SW track. It means a whole week of surf for North Island
eastern beaches, with the wind swing making my pick for the best surfing
waves in Hawke's Bay to be on Wednesday and Thursday.
From Thursday a change of pattern is expected with troughs moving onto
NZ from the southwest - one of these may deepen into a large low
crossing central NZ by Sunday 18th.

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

04 January 2009

BOBGRAM7 issued 4 Jan 2009

WEATHERGRAM
YOTREPS
Issued 4 JAN 2009  
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.
Welcome all to 2009 --- we are entering this year with a trend away from Neutral territory and towards a weak LA NINA.

TROPICS
TC BILLY went west off NW Australia, briefly grew to hurricane force and then faded.
The EC model is picking that another TC may form in the Gulf of Carpentaria this week, reaching a peak as it makes landfall going west early next week.
The South Pacific Convergence Zone SPCZ stretches from the northern Coral Sea to northern Vanuatu to the Rotuma area. There are now some squally westerly winds on its northern side between Solomons and Tuvalu.
 A MJO, or pulse of extra activity, is wandering east across the Coral Sea area this week, and this may help form low centres on the SPCZ. 
There is already one showing to northwest of New Caledonia. Computer models are coming up with different scenarios for the lows between the Coral Sea and Norfolk Island area.  Isobars around these lows will squash closer together in a zone to the south (in the easterly winds) and another zone to north and east (in the northwesterly winds along the SPCZ).
Any lows that do form are likely to head for the area between New Caledonia and Norfolk Island.
Another branch stretches between northern cooks and southern French Polynesia.  This zone is likely to move southwards this week, with lows possibly forming on it over southern Tonga heading for the Kermadecs and another near the Southern Cooks.  It is a good week to stay ashore.
SUBTROPICAL RIDGE
Eastern flank of the HIGH over the NZ area is expected to move off to the east enhancing the trade winds along 30S between 180 and 140W.  The western flank is expected to stall to west of NZ and fade away on Thursday.
TASMAN SEA/NZ
The front that crossed NZ on Saturday was preceded by a north to northwest flow that brought rain to the north and hot dry conditions to the east.  The southerly that followed was egged on by rising pressures of the HIGH.  It arrived in Canterbury at the right time of day to produce squally hail.
 The next front that will be followed on by an accompanying HIGH is expected to cross the Tasman on Thursday or Friday and reach the South Island on Friday or Saturday.  Models are divided as to whether this front does a repeat of the last front or stalls maybe around central NZ.
Its track is somewhat dependant on the behaviour of the Low that will then be near Norfolk Island.
 There will be a trough connecting these two systems and that will complicate things.  
Those intending to cross the Tasman Sea should keep checking updates.
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

Blog Archive