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

30 August 2009

BOBGRAM7 issued 30 Aug 2009

WEATHERGRAM
YOTREPS
Issued 30 August 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/SUBTROPICS
Looks as though it is the peak of the cyclone season now in the Northern
hemisphere with activity in the western and eastern North pacific and in
the Atlantic... but I think TC Danny will weaken offshore as it heads
along the Gulf stream... maybe making landfall over Nova Scotia
something like Bill did.

As for the South pacific - well, the main part of the South Pacific
convergence Zone SPCZ remained in a northern-most position last week and
is likely to do so this week as well (this is where it liked to be in El
Nino) from Solomons to Tuvalu to Tokelau, and from there it forks with
one section along Northern cooks and French Polynesia and another
section across Southern Cooks.

There is likely to be a tropical trough forming over Fiji around wed 2
sep UTC (they had dry weather there during Hibiscus festival last week,
so this trough may bring some welcome rain). This trough is likely to
wander east, propelled along by westerly winds aloft. It should reach
Southern Cooks area by sun 6 sep UTC. Windy wet northerlies precede
this trough , and as it makes its way east wards across the tropics it
will kill the trade winds, and may even be followed by s cool dry
southerly for a few days. Time yourself around it.


SUBTROPICAL RIDGE
A HIGH that is today south of Niue is wandering east along 30S. An
associated squash zone of enhanced trade winds is today from around
Suvarov to Samoa and this squash zone will track east along the north
side of the HIGH and reach French Polynesia around Thu 3 Sep UTC and
then fade.

Next High is expected to build in the central Tasman Sea on Wed 2 Sep
UTC and cross NZ on Thursday at around 40S and then fade in the south
and retract to the normal 30S latitude.

TASMAN/NZ AREA
Unusually intense front is crossing NZ tonight, along with a companion
LOW sliding south out of the Tasman Sea.

A weaker front is expected on Tue 1 Sep, however that front is expected
to deepen into a big LOW near the dateline/40S on Thursday/Friday... and
that development, in cahoots with a HIGH in the Tasman should feed a
cold southerly flow onto eastern NZ especially on late We3d, Thu, and
early Fri.

Next front is likely on Sat 5 Sep UTC, and this front may linger when it
reaches the north Tasman Sea, waiting for a LOW to deepen in the Tasman
early next week.

So it's a week of possible weather windows for sailing in all direction
around NZ, and, after tonight's front, the strong winds should stay away
for a while (but avoid the southerlies on the Hawke's Bay coast on
Thu/Fri).


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

23 August 2009

BOBGRAM7 issued 23 Aug 2009

WEATHERGRAM
YOTREPS
Issued 23 August 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.

Apologies for delayed sending of this email--- 'twas a server problem

TROPICS/SUBTROPICS
We start the week with TCs Bill, Hilda and Vamco in the Atlantic, NW and
NE Pac respectively. Bill should sideswipe Nova Scotia, Hilda should
fade south of Hawaii, and Vamco should wander north.
As for the South pacific - well, the main part of the South Pacific
convergence Zone SPCZ has wandered to the northern part of its zone..
from Solomons to Samoa to Southern Cooks. There should be a burst of
activity near the Southern Cooks on Monday /Tuesday UTC, and another
between Tuvalu and Samoa /Tonga on Sunday and Mon 30/31 Aug UTC.

SUBTROPICS
The High positioned in the North Tasman Sea and covering New Caledonia
today is expected to move along 30S and fade near the date line on
Wednesday, enhancing the trade winds in the Coral Sea.
Next High is expected to be stronger and larger, and should build in
the Tasman Sea near 33S on Thursday, Cross the North Island on Friday,
and
Wander east along 33S after that reaching French Polynesian longitudes
on 1/2Sep, all the while with a squash zone of enhanced trade winds on
its northern side. As it wanders east of 140W around 2 Sep, a LOW
should form on its North-western shoulder near Niue. Avoid.

TASMAN/NZ AREA
That LOW which has been hovering off the NE of NZ last few days should
wander slowly along 30S as a multi-centred feature with one of the
centres deepening at 30S near 155W or south of French Polynesia on
Wednesday, bringing them a touch of westerly winds on Wednesday and
Thursday UTC.
A front is fading over north-western NZ this evening. Next front should
move onto SW of South Island on Tuesday and North Island on Wednesday
proceeded by northerly winds and followed by a northwest flow.
On Thursday another front should cross NZ proceeded by NW winds and
followed by westerlies. This front may well have thunderstorms.
Next front is likely to reach SW of south Island late sat and cross NZ
on Sunday, preceded by NW flow and followed by a S to SW flow. This
front is probably the best of the bunch for going north but still not
ideal.

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

BOBGRAM issued 23 Aug 2009

WEATHERGRAM

YOTREPS

Issued 23 August 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/SUBTROPICS

We start the week with TCs Bill, Hilda and Vamco in the Atlantic, NW and NE Pac respectively.   Bill should sideswipe Nova Scotia, Hilda should fade south of Hawaii, and Vamco should wander north.



As for the South pacific - well, the main part of the South Pacific convergence Zone SPCZ has wandered to the northern part of its zone.. from Solomons to Samoa to Southern Cooks.  There should be a burst of activity near the Southern Cooks on Monday /Tuesday UTC, and another between Tuvalu and Samoa /Tonga on Sunday and Mon 30/31 Aug UTC.



SUBTROPICS

The High positioned in the North Tasman Sea and covering New Caledonia today is expected to move along 30S and fade near the date line on Wednesday, enhancing the trade winds in the Coral Sea.



Next High is expected to be stronger and larger, and should build in the Tasman Sea near 33S on Thursday, Cross the North Island on Friday, and 

Wander east along 33S after that reaching French Polynesian longitudes on 1/2Sep, all the while with a squash zone of enhanced trade winds on its northern side.    As it wanders east of 140W around 2 Sep, a LOW should form on its North-western shoulder near Niue. Avoid.



TASMAN/NZ AREA



That LOW which has been hovering off the NE of NZ last few days should wander slowly along 30S as a multi-centred feature with one of the centres deepening at 30S near 155W or south of French Polynesia on Wednesday, bringing them a touch of westerly winds on Wednesday and Thursday UTC.



A front is fading over north-western NZ this evening.  Next front should move onto SW of South Island on Tuesday and North Island on Wednesday proceeded by northerly winds and followed by a northwest flow.



On Thursday another front should cross NZ proceeded by NW winds and followed by westerlies.  This front may well have thunderstorms.



Next front is likely to reach SW of south Island late sat and cross NZ on Sunday, preceded by NW flow and followed by a S to SW flow.  This front is probably the best of the bunch for going north but still not ideal.







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

16 August 2009

BOBGRAM7 issued 16 Aug 2009

WEATHERGRAM
YOTREPS
Issued 16 August 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/SUBTROPICS
After a few weeks of atrocious weather, it now seems to be settling down
now around South China and Philippines. In fact the coming week should
be drier than normal there, but TCs are still being produced on the
ITCZ - one near the dateline (TC MAKA) and another SE of Hawaii (TC
GUILLERMO, should go NW and get north of Hawaii) so take care there.

As for the South pacific - well, the main part of the South Pacific
convergence Zone SPCZ seems to have settled to be slightly north of
where it was a few weeks ago, and is now over Solomons to
Fiji/Wallis/Futuna to Tonga area. It isn't expected to travel much from
this placement over the next week or two, and that means some parts of
this zone will be getting real soggy. Vey likely an intensification of
activity may pulse along the SPCZ late this week, over Solomons on
Friday and reaching Tonga/Niue on Saturday /Sunday 22/23 Aug. Avoid.

There seems to be an increase in convection in the zone along 5S to 10S
from 180 to 140W. Over the next month or so the overhead sun will be
heading for the equator, and this typically causes a twinning of the
ITCZ with a mirror zone between 5 and 10S--- so maybe this mirror zone
is starting to form. I'll keep an eye on this.

SUBTROPICS
There has been some blocking but its eased now, so we are in for a
change in weather pattern.

The remains of last week's big fat high BFH are today around 1032 near
35S 160W, bringing enhanced trade winds on its northern since to between
southern French Polynesia and southern Cooks - all fading away by end of
Tues 18 Aug GMT as that high continues on its easterly migration.

Two more highs will enter our arena this week, but not as big as last
week's.

The first is already entering the North Tasman Sea and should feed a
squash zone in the northern Coral Sea until Tuesday that may briefly
stretch east to Rotuma.

The second should be larger than the first and bud off Australia and
expand across the central Tasman Sea on Wednesday, with a strong SSE
squash zone over New Caledonia and the full Coral Sea. This high is
likely then to contract northwards and become a slow-moving high that
will hug 30S and not reach 180 until end of next week /29 Aug. It
brings some reliability to the weather I suppose-and this weather
pattern is typical of El Nino.

TASMAN/NZ AREA
Between these migratory highs are lows and troughs... one is bringing a
southerly and welcome rain to eastern North Island tonight.

Next front is expected to fracture as it moves from Tasman Sea onto NZ
on Tuesday. There will be some wicked southerly winds following it, may
bring more welcome rain to eastern NZ (and snow to the mountains), and a
sling shot to anyone wanting to sail northwards.

This should be followed over NZ by a one-day-ridge on Thursday 20 and
then a disturbed westerly flow from Friday 21 to Wednesday 26 August
(avoid sailing with these), with an outlook of another one-day-ridge on
Thursday 27 Aug and then very strong NW winds at the end of next week,
bringing a warm spell that will end winter.

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

08 August 2009

BOBGRAM7 issued 9 Aug 2009

WEATHERGRAM
YOTREPS
Issued 9 August 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.

EL NINO UPDATE
During July the warming trend in the Pacific Equatorial Ocean exceeded
the threshold that is sufficient for this to be called the beginning of
a new El Nino episode. Since then this warming trend seems to have
stalled. As far as the weather patterns are concerned (looking
retrospectively) there hasn't been much sign of an El Nino yet. Its
normal for the atmosphere to lag behind the ocean like this. The
seasonal outlook is for some El Nino activity to show itself in the
South West Pacific during the coming spring-- Basically the weather
patterns will likely be drawn closer to the equator, with lighter trade
winds and with the South Pacific Convergence zone shifted northwards and
eastwards. It is still too early to draw much idea of the coming
cyclone season--- The overhead sun doesn't get to 10S until November,
and that's months and months away, and things can change. However,
since anxious cruisers like to worry about these things, if El Nino is
around in November then some tropical cyclones (which seem to like to
form on the SPCZ) may likely form in the Samoa to French Polynesia zone,
so that's a zone worth moving away from beforehand.

TROPICS/SUBTROPICS
There is a burst of westerly/southwesterly winds in the NW Pacific about
the Philippines, and this area will be a possible area of enhanced
convection and breeding area of lows. The ITCZ is active to southeast
of Hawaii, and anyone near there needs to stay tuned to TC FELICIA's
update-however it looks as though it may fade as it approaches Hawaii.

As for the South pacific - well, this week is not showing any El Nino
signs. The South Pacific Convergence Zone SPCZ, is lying from Papua New
Guinea to Northern Vanuatu/Rotuma, with another branch lying from Niue
to south of French Polynesia. The western branch may move south this
week and reach New Caledonia area or between New Caledonia and Fiji by
the end of this week--- helping form a low between Fiji and NZ around
13-14 August.

SUBTROPICS
A big fat High near 1040 hp over Chathams is expected to move slowly
northeast and fade this week -- that will enhance the easterly winds
along 20S from French Polynesia to Tonga.

A weak High is marching steadily along 55S to south of the Australian
Bight and looks as though it will cross the South Island on Wed/Thu
12/13 Aug and then join the BFH. Another weak high is expected to form
over southern QLD on Sat 15 August but then fade. So I hope people have
been enjoying this BFH while it has visited us, for it is unknown when
the next High will get to NZ.

TASMAN /NZ AREA
Lows are forming in the Tasman Sea, on the western shoulder of the BFH.
The BFH is such that these lows are being shunted south out of the
Tasman, but there are strong NE to N winds over NZ, between the Tasman
and the BFH.

Around Thursday or Friday the SPCZ may help form a subtropical low to
north of NZ, and by then the BFH may be sufficiently off to the east,
so that this low can run southwards right across the North Island on
Friday Saturday Sunday. Avoid.

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

01 August 2009

BOBGRAM7 issued 2 August 2009

WEATHERGRAM
YOTREPS
Issued 2 August 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/SUBTROPICS
The South Pacific Convergence Zone reformed last week at the northern
extent of its range - across Solomons/Tuvalu to Samoa, and then east
southeastwards across French Polynesia FP .

This week the SPCZ is likely to drift southwards as a new Madden Julian
Oscillation (boost of tropical convection) advances into the western
Pacific from Australia. By the end of this week it should stretch
across the Coral Sea towards the Loyalty Islands area/maybe New
Caledonia and then southeastwards towards Kermadecs. Another branch is
likely to stretch from Northern Tonga to southern parts of French
Polynesia.

A tale of two lows; At the south end of each branch of the SPCZ a low
is likely to form this week, disrupting the otherwise steady trade wind
flow. The Low that is forecast to form near 20S 140W on Thursday 6 Aug
UTC (call it L1) should move southeast and deepen below 10000, and is
likely to kill the winds over the main part of FP in the process.

The low that is likely to form near New Caledonia or the Loyalty Islands
on or around Sat 8 Aug UTC, call it L2, is at this stage forecast to
deepen to around 1006 and become complex as it moves south towards North
island early next week.

Avoid these lows, or maybe use them as clockwise wind swings.

During the coming week a weak trough is likely to remain
quasi-stationary to north of 30S between NZ and Fiji: Its eastern side
is wet with northerly winds, and its western side is relatively dry with
S to SE winds.

SUBTROPICS
The remains of last weeks big fat high BFH is quasi-stationary near 35S
115 to 145W, enhancing the trade winds between 20 and 25S on its
northern side. However, its western flank is expected to fade when L1
forms over southern FP around 6 Aug. Avoid the squash zone between the
high and L1.

A weak high cell is expected to chug along 32-35S from east of NZ on Mon
3 Aug to 170W on Thu 6 Aug and there fade.

A new high cell is likely to form in the Tasman Sea on Thu 6 Aug and to
cross central NZ on Fri 7 Aug and then build to over 1030 east of NZ,
near 35-40S 160-170W, this weekend and early next week. Beware the
squash zone between it and L2--- these strong NE winds make sailing from
NZ to Tonga a bad idea from 8 to 12 Aug.

TASMAN /NZ AREA
A long-wave trough LWT is stuck over the Southern Bight and its
ridge-buddy is stuck over 180. The LWT is generating fronts and tossing
them across the Tasman at the rate of around one every other day.

These fronts do not really have attached lows associated with them and
vary in intensity and are generally decaying as they cross NZ, but have
guts in them when the reach our SW end. There is one crossing the
North Island this evening (Sunday 2 Aug), next one is due Tuesday and
then a weak one on Thursday and another on Saturday. These fronts are
preceded by NW flows that concentrate the rain on the western slopes of
the main divide and bring Foehn warming downwind into the rain-shadow.
Yes, this is typical of an El Nino.


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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