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

25 October 2009

BOBGRAM7 issued 25 Oct 2009

WEATHERGRAM
YOTREPS
Issued 25 October 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.

NIWA, Fiji Met Service and BoM have all produced much the same outlook
for the coming cyclone season. The El Nino observed in the Ocean was
not having much impact on weather patterns in the atmosphere as measured
by the SOI (until the last week or so). Computers are expecting the
main coupling between ocean and atmosphere to occur around December and
January. Indications are for around 8 cyclones in the South West
Pacific this season (the normal is 9). Countries east of 180 are at a
higher risk than normal. 2 or 3 cyclones may reach at least Category 3
and one may reach at least category 4. The first storm is likely to
develop before the end of December.

There are still cyclones in the Northern Hemisphere-LUPIT near eastern
Japan and NEKI over western islands of Hawaii. Last weeks burst of
equatorial westerlies last extended eastwards to beyond 170E and is
likely to affect Kiribati and Tuvalu this week, affecting west-facing
harbours.

South pacific convergence zone, hugging 10S between Solomons and
Tokelau, has west to northwest winds on its northern side and a squash
zone of trade winds on its southern side along 15S. The SPCZ is showing
signs of moving south and may extend as far south as Fiji by Wednesday
28 Oct, perhaps developing a low between Samoa and northern Tonga that
will extend southeast wards across southern Cooks by 30 Oct UTC... Also
SPCZ may develop a low in the Coral Sea, south of Solomons on 27 Oct
that may stall and then shift west-wards and fade away around 31 Oct
UTC. In any event, the strong SE winds in the central Coral Sea and
expected to last all week.

SO the SPCZ is worth avoiding this week.

CROSSING THE SUBTROPICS and HEADING FOR NZ ... Maybe not this week...
High pressures in the Tasman Sea this week and low pressures to east of
NZ team together so that we have south and southwest winds between NZ
and Tonga over next few days and so no offering of a good sail. This
southwesterly is expected to reach Minerva around Tuesday 27 Oct and
Nukualofa around Wednesday 28 Oct and last around 2 days so that the
next "weather window" for departing from Tonga NZ may open around Friday
30 Oct, perhaps a little later. .

Approaching NZ from New Caledonia or from Australia may be OK this week,
but avoid the SW flow near the North Island on Tuesday and Thursday -
passing fronts may have gale winds and high seas.

In detail: A LOW is forecast to deepen as it crosses central NZ on
Monday and as a HIGH forms in the South Tasman Sea - so that a SW gale
in-between these systems focuses in the area west of the North Island
and reaches a peak Tuesday UTC. The High then fades and stalls on
Wednesday as the Low moves off the east and weakens. But by late
Wednesday and during Thursday a trough deepens east of and over NZ as a
new High builds in the Tasman Sea - in-between will be a vigorous cold
polar outbreak of southerly winds.

That new High is forecast to cross NZ on Sunday and Monday bringing NZ a
break in the SW weather.

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 October 2009

BOBGRAM6 issued 18 Oct 2009

WEATHERGRAM
YOTREPS
Issued 18 October 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 the migration season when several yachts shift in
the Southern Hemisphere from Tropical to middle latitudes.

There are still cyclones forming in the NW Pacific, LUPIT, and near
Mexico , RICK. There was burst of equatorial westerlies to north of
Papua New Guinea for much of last week, and an attempt at forming a TC
just north of Solomons, but nope, not yet. It looks as though South
Pacific will not be ready for a few weeks yet, maybe a month or more.

The ocean temperatures are consistent with an El Nino episode; the
Southern Oscillation index is hovering around neutral but starting to
lean in an El Nino direction. NIWA (NZ) and BoM (OZ) will be issuing
their cyclone outlook this week at
http://www.bom.gov.au/weather/cyclone/NatOutlookNotice.pdf
and (NIWA's Island Climate Update for Oct) at
http://www.niwa.co.nz/our-science/climate/publications/all/icu

South Pacific Convergence Zone SPCZ has been most active across the PNG/
Solomons doldrums area and then along 10S as far as Tokelau and then
between the Northern and Southern Cooks and across French Polynesia.
This location is further north and east than normal, as found in a El
Nino episode. Most likely the SPCZ will be drifting south over next few
weeks...should visit Samoa on 20 Oct, and Wallis/Futuna/northern Tonga
on 22-25 Oct, and Fiji/Southern Tonga on 26-28 Oct.

Winds in the Coral Sea have been strong SE last week and will be strong
SE until 24 Oct due to high pressure in the Tasman Sea. Anyone sailing
Vanuatu /New Caledonia to Australia this week are in for a bouncy rides.


CROSSING THE SUBTROPICS and HEADING FOR NZ

The thing to do when planning such a trip is to avoid squash zones
(where isobars are squeezed together as highs go by) and fronts. Try to
reach Northland between fronts - that means working out the average
timing of fronts reaching Northland. This is hard because weather
output is only good for a few days and your trip may take a week.
Usually if you deliberately arrange to go thru a front at 30S (where
they are usually weak) then that will give you a gap between fronts for
your landfall.

This week the subtropical high is the main features to watch............


The High forming offshore Sydney on Mon 19th is expected to move NE and
stall near Norfolk Island on 22 Oct. It will need to wait for a series
of fronts and troughs to make their way NE across eastern NZ, one on 19,
and another on 21 to 23 Oct --- so much of this week there will be
southerly winds over Northland (between Tasman high and the troughs to
the east).

However, after 23 Oct, that High is expected to poke its tongue out and
along 33S, followed by a NW flow -making a reasonable wind for landfall
in Northland for sailing from New Caledonia/Fiji/Tonga between 24 and 27
Oct. At this stage this window closes over Northland, for those coming
from Tonga anyway, around 28 Oct when next trough is expected to reach
Northland.

To work in with this window you will need to arrange to get to the
subtropical ridge (30-33S) by around 23 Oct.

For those in New Caledonia: there will be something of a squash zone of
the north side of that high when it is in the central Tasman Sea, so
you may need to sail SSW first when heading to NZ.

For those in NZ looking forward to the Coastal Classic:
Front reaching Auckland on Friday morning is the last in a series of
fronts and should be followed by that High then near Norfolk Island.
SO, at this stage, the outlook if for a stiff SW wind that may weaken
Friday night and briefly swing SE. EC model makes more of this SE at
present than do the other models, so it may be a fast race.

The current EC model deepens a low off Sydney on Sun 25 Oct --- this has
only a 30% chance of happening at this stage, so recheck.

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

11 October 2009

BOBGRAM7 issued 11 Oct 2009

WEATHERGRAM
YOTREPS
Issued 11 October 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.

Vanuatu Quake--- this was a sideways shake so didn't toss the sea around
too much. Phew.

Palolo (or Balolo in Fiji): These worms rise out of the coral reefs for
a spawn-fest in the waning moon of Oct and Nov (around now), that's if
they haven't been upset by recent events. Anyway ask the locals,
something to do while waiting for a good voyage south,

Northwest pacific cyclone season - because the names used tin that
region cover several language with different scripts they don't go
alphabetically in the English alphabet after all. Thanks to those who
picked me up on my surprise at the jump from KETSANA to PARMAR/MELOR
last week.

MELOR was a real super cyclone for a while and managed to mostly miss
Guam, then smashed into south-eastern Japan, killing 5 and injuring
around 100.

In the South Pacific the Convergence Zone SPCZ has split into two, with
one branch from around Solomons to near Fiji, and another branch from
Tokelau across Northern cooks and touching between central French
Polynesia and Marquesas-a rare northeastern position for the SPCZ.

I think the western branch will move onto Tonga around mid week, and a
Low may form between Tonga and Niue on 14 Oct then move southeast and
deepen as it feeds off an upper jet stream. SO that may keep yachts in
Tonga while yet.

There has been an equatorial westerly during the last week between
Solomons and Micronesia, and GFS model is trying to produce a Low over
the Solomons area out of this later this week... but EC model doesn't.
In this case I'm inclined to agree with the EC.

Winds in the northern Coral Sea were strong last week but should relax
over next few days as a trough crosses the Tasman. They are likely to
get strong again
For 17 to 24 Oct as another High crosses the Tasman and this strong wind
zone is likely to affect New Caledonia from 18 to 22 or 23 Oct, so see
if that times in with your plans around there.


TONGA to NZ/ CROSSING THE SUBTROPICS
As said before- a weak part of SPCZ should visit south Tonga around
12-13 Oct and a low may form on this near Niue on 14 Oct. If you are
already at Minerva you may miss this, or perhaps can see it overhead
tonight.

In tandem with this, the HIGH over Tasman Sea today already pokes a
tongue of ridge towards NE of North Island and should travel east along
this axis maintaining a reasonable subtropical ridge between Tonga and
NZ, at 30S anyway, until 17 Oct. Although this is a nice enough ridge
to sail across the subtropics with, the problem is timing - it will get
you to NZ just when the next big trough arrives, frontal zone around 17
oct followed by a couple of days of SW to S winds. Either avoid or work
out a coping path.

BTW this trough is likely to breed a 988 Low over Tasmania in Tuesday,
avoid. Its first front should cross NZ on Wed 14 Oct and may be
somewhat thundery, announcing the return to spring over NZ after 3
winter-like lows.

Next HIGH from Australian bight should cross New South Wales on 17-18
Oct and Tasman on 19-21 Oct. So there is a possible window: a yacht
capable of up to 6 knots could possibly depart Vavau around 14 Oct, go
thru the "17Oct NZ front" in a weakened state at 25S on 19Oct and then
have SE winds on the beam for the rest of the trip to NZ -between low
near south of Niue and High in Tasman Sea, reaching Opua in light winds.
But this scenario may well change so you'd need an update before
departing.


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 issued 11 Oct 2009

WEATHERGRAM
YOTREPS
Issued 11 October 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.

Vanuatu Quake--- this was a sideways shake so didn't toss the sea around
too much. Phew.

Palolo (or Balolo in Fiji): These worms rise out of the coral reefs for
a spawn-fest in the waning moon of Oct and Nov (around now), that's if
they haven't been upset by recent events. Anyway ask the locals,
something to do while waiting for a good voyage south,

Northwest pacific cyclone season - because the names used tin that
region cover several language with different scripts they don't go
alphabetically in the English alphabet after all. Thanks to those who
picked me up on my surprise at the jump from KETSANA to PARMAR/MELOR
last week.

MELOR was a real super cyclone for a while and managed to mostly miss
Guam, then smashed into south-eastern Japan, killing 5 and injuring
around 100.

In the South Pacific the Convergence Zone SPCZ has split into two, with
one branch from around Solomons to near Fiji, and another branch from
Tokelau across Northern cooks and touching between central French
Polynesia and Marquesas-a rare northeastern position for the SPCZ.

I think the western branch will move onto Tonga around mid week, and a
Low may form between Tonga and Niue on 14 Oct then move southeast and
deepen as it feeds off an upper jet stream. SO that may keep yachts in
Tonga while yet.

There has been an equatorial westerly during the last week between
Solomons and Micronesia, and GFS model is trying to produce a Low over
the Solomons area out of this later this week... but EC model doesn't.
In this case I'm inclined to agree with the EC.

Winds in the northern Coral Sea were strong last week but should relax
over next few days as a trough crosses the Tasman. They are likely to
get strong again
For 17 to 24 Oct as another High crosses the Tasman and this strong wind
zone is likely to affect New Caledonia from 18 to 22 or 23 Oct, so see
if that times in with your plans around there.


TONGA to NZ/ CROSSING THE SUBTROPICS
As said before- a weak part of SPCZ should visit south Tonga around
12-13 Oct and a low may form on this near Niue on 14 Oct. If you are
already at Minerva you may miss this, or perhaps can see it overhead
tonight.

In tandem with this, the HIGH over Tasman Sea today already pokes a
tongue of ridge towards NE of North Island and should travel east along
this axis maintaining a reasonable subtropical ridge between Tonga and
NZ, at 30S anyway, until 17 Oct. Although this is a nice enough ridge
to sail across the subtropics with, the problem is timing - it will get
you to NZ just when the next big trough arrives, frontal zone around 17
oct followed by a couple of days of SW to S winds. Either avoid or work
out a coping path.

BTW this trough is likely to breed a 988 Low over Tasmania in Tuesday,
avoid. Its first front should cross NZ on Wed 14 Oct and may be
somewhat thundery, announcing the return to spring over NZ after 3
winter-like lows.

Next HIGH from Australian bight should cross New South Wales on 17-18
Oct and Tasman on 19-21 Oct. So there is a possible window: a yacht
capable of up to 6 knots could possibly depart Vavau around 14 Oct, go
thru the "17Oct NZ front" in a weakened state at 25S on 19Oct and then
have SE winds on the beam for the rest of the trip to NZ -between low
near south of Niue and High in Tasman Sea, reaching Opua in light winds.
But this scenario may well change so you'd need an update before
departing.


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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