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

29 January 2011

BOBGRAM7 issued 30 Jan 2011

WEATHERGRAM
YOTREPS
Issued 30 January 2011
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.

La NINA is still strong. Average atmospheric SOI over 30 days ending 27
Jan is 1.87 (a drop of 0.54 since 21 Jan). .

TROPICS
WILMA followed its expected track and sideswiped Northland and eastern
Bay of Plenty Friday night/Saturday.

ANTHONY lost its top clouds when it re-curved a few days ago, but has
managed to grow some more and get re-named , it now weakening again and
should make landfall between Townsville and Mackay overnight tonight/
around 1am Monday local time.

Another tropical low, just named YASI, is now deepening as it approaches
northern Vanuatu from the east. It is expected to become a major
system and keep going west, gathering energy over the Coral Sea. At
this stage, it is on track to make landfall between Townsville and
Cairns on Thursday 3 Feb UTC. Avoid.

YASI is likely to end this period that has allowed the formation of a
cluster of cyclones, and gradually allow a return of trade winds to the
South Pacific around 5/6 Feb. The South Pacific Convergence Zone SPCZ
has been broken into pieces over past few weeks and should start
reforming along 10 South next week.

SUBTROPICAL RIDGE: STR/ NZ Area.
High/ridge has shifted to 35S in the North Tasman Sea by a shift
northwards of cold air from the roaring 40s. The front responsible for
this northern shift crossed South Island last Friday in time to capture
WILMA and kick it southeastwards, thus limiting its impact on NZ
(thanks).

This high cell is likely to be held in place by an upper ridge until the
5/6 Feb weekend, when it should migrate to east of North Island.

So, it looks like a week of disturbed westerly flow over NZ, with fronts
weakening over the South Island on Monday, Tuesday/Wednesday and Friday.
These fronts may each bring a period of NW gales to eastern districts
and heavy rain about and west of the South Island divide.

Next high is likely to form in Aussie Bight around Sat 5 Feb and move
into Tasman Sea around Sun 6 Feb (Waitangi Day holiday in NZ), pushing a
substantial cold front as S/SW change over NZ. Avoid this cold front.


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

22 January 2011

BOBGRAM7 issued 23 Jan 2011

WEATHERGRAM
YOTREPS
Issued 23 January 2011
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.

La NINA is still strong. Average atmospheric SOI over 30 days ending 22
Jan is 2.41 (a slight drop of .05 since 12 Jan). .

TROPICS
Two new cyclones named today. Fiji Met Service is following WILMA: its
centre is likely to circle clockwise to north of Samoa then some south
near America Samoa on Monday and southwest-wards across Tonga on Monday
and Tuesday. At this stage, it may get near Raoul Island on
Wednesday/Thursday and after that track is uncertain. Avoid.

Brisbane Bureau is following ANTHONY, which has formed in the Coral Sea
east-northeast from Cairns. It is currently heading east and should
feed on the warm seas of central Coral Sea over next few days....growing
and growing. This growth is likely to cause the system to loop near 156E
on late Tuesday/Wednesday and then to wander back to WNW where it may
make landfall on far north Queensland over weekend or early next week.
Uncertain at this stage. Avoid.

Another cyclone may form in the Vanuatu to Fiji area around Sun 30 Jan.

The low that deepened to around 990 hPa as it travelled southeast away
from New Caledonia on Saturday is crossing north half of North Island
tonight, taking a track along a trough that was left behind by former
ZILIA. This coincides with a King Tide around midnight. It has gales
around its centre and has already shunted a zone of heavy rain on ahead.
Avoid.

These weather systems have been FAST and FURIOUS lately.

SUBTROPICAL RIDGE: STR.
High/ridge with light winds settling over North Island late Monday 24
Jan and moving off to east on Thu 27. Next High should cross Tasmania
on Fri 28 Jan and then cross North island Area around Sun 30 Jan to
Tuesday 1 Feb, but may have to wait for WILMA's remnants.


NZ AREA.
Remnants of WILMA may be coming south on Fri/Sat 28/29 Jan as a trough
(transitional between highs) crosses the Tasman Sea/NZ area. Details
uncertain at this stage, so if this may affect your plans then watch for
updates. In any event, there should be a new southerly change sweeping
away this trough on Sun 30 Jan, so outlook for Auckland anniversary day
regatta on Mon 31 Jan at this stage is for a dying SW flow.

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

15 January 2011

BOBGRAM7 issued 16 Jan 2011

WEATHERGRAM
YOTREPS
Issued 16 January 2011
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.

La NINA is still strong. Average atmospheric SOI over 30 days ending 12
Jan is 2.48 (an increase of 0.18 in the past week). In a La Nina
episode, isobars are lower than normal over northern Australia and
higher than normal over Tahiti. The NZ area is then "piggy-in-middle"
and generally gets more northerly flow than normal. The 2.48 SOI is a
good measure of the extent of abnormality in the weather over northern
Australia. .

TROPICS
We are entering one of the likely busy times of this cyclone season.

South Pacific Convergence Zone SPCZ lies mainly from central Coral Sea
across Vanuatu to Southern Cooks. It is very broad and active, and
early last week heavy rains deluged over Fiji. On Wednesday, TC VANIA
formed. It peaked on Friday, as anticipated in last week's weathergram,
near eastern New Caledonia.
TC Zelia formed on Friday and appears to be reaching its peak tonight
/Sunday as it approaches south end of New Caledonia. It should weaken
back to a tropical Low on Monday 17 Jan.

A Madden Julian Oscillation MJO or pulse of enhanced convection seems to
be making its way into the northern Coral Sea this week. This increases
the chances of tropical cyclone development. A good sign this is indeed
happening is the arrival of equatorial westerly and NW winds over North
Australia. These winds are expected to spread into the northern Coral
Sea over next few days and reach Solomons to Tuvalu by the end of this
week.

Next tropical system to develop is likely to form in western Coral Sea.
GFS & NOGAPS models at present have this occurring around Thu 20 Jan and
EC model by around Mon 24 Jan. Initial ideas are for this system to
track towards New Caledonian area and maybe another system to form near
Fiji as this happens. Plan around these systems.


SUBTROPICAL RIDGE: STR.
New High is expected to ridge across New South Wales on Mon /Tue 17/18
Jan and as it crosses the South Tasman Sea on Wed 19 Jan should link
with a High that had budded north from the Polar Regions to Campbell
Island. This combined High should move NE to area-that-is-east-of-NZ
from Thu 20 to Thu 27 January and expand slowly maybe peaking at around
1038+ next week at 45S to south of the Cooks-this is consistent with La
Nina. There have been very few interruptions in the enhanced easterly
flow over northern Tasman Sea over past six weeks, and this system may
not last long enough but is providing some half-decent trans-Tasman
voyages for a change.

NZ AREA.
Remnants of VANIA are west of Norfolk Island today and heading south and
expected to move southeast across South Island or central NZ on Tuesday.
This coincides with arrival over Southland of LOW from Tasmania. This
LOW has been made from a lot of moisture that has been bothering
Victoria over past few days AND it is followed by a sub-polar high. SO,
on late Tuesday/ early Wednesday, ingredients are in place for a rapidly
deepening low east of the South Island, just as remnants of ZELIA move
southeast across the North Island. Avoid.


On Thursday, conditions should clear nicely with a dying southerly. On
Friday, for Auckland's Big Day Out, an easterly flow is expected to
settle in over North Island along with a lingering trough.

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 January 2011

BOBGRAM7 issued 9 Jan 2011

WEATHERGRAM
YOTREPS
Issued 9 January 2011
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.

La NINA is still strong. Average atmospheric Southern Oscillation Index
SOI over past 30 days is 2.3 (a drop of 0.16 in the past week). Dec SOI
was 2.7, a new Dec record and we have to go as far back as Nov 1973
(3.16) to find a higher SOI. This indicates the extent of abnormality
in recent Australian weather maps. Oceanic Nino Index for Sep-Oct-Nov
is -1.4

TROPICS
South Pacific Convergence Zone SPCZ lies mainly from central Coral Sea
across Vanuatu to Samoa and then SE to east of Niue. This is currently
activating between Vanuatu and Fiji and a Tropical Low has formed near
17S 172E.

This system is expected to go SW and pass by close to south end of
Vanuatu, then south then go SE and peak near 25S 173E around Fri 14 Jan
and then weaken over or near North Island area on Sun 16 mon 17 Jan.
Avoid.

Equatorial westerly winds are still well west, just entering the
western Timor sea this week. They are late. A tropical low system should
form off NW Australia around Friday 14 Jan and move off to the SW.

SUBTROPICAL RIDGE: STR.
High in South Tasman Sea is expected to stay there and fade away
allowing a trough and SW outbreak to cross eastern NZ on Wed 12/ Thu 13
Jan . Then a new High 1032+ should roll in from Australian Bight and go
NE across Tasman Sea on Thu Fri 13-14 Jan , and then move quickly away
eastwards along 37S on Sat 15 Jan.

So we have a mobile high crossing the Tasman Sea - this will be useful
for those seeking to escape from Queensland.

TASMAN SEA/ NZ AREA
By Thu 13 Jan Low from central Australia (full of monsoonal moisture) is
expected to move south across Adelaide area and into Australian Bight.
This Low should then wander east along 50S, affecting Tasmania on Fri 14
and Southland on Sun 16. 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

02 January 2011

BOBGRAM7 issued 2 Jan 2011

WEATHERGRAM
YOTREPS
Issued 2 Jan 2011
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.

La NINA is still strong. Average atmospheric SOI over 30 days ending 2
Jan is 2.56 (an increase of 0.26 in the past week). Oceanic Nino Index
for Sep-Oct-Nov is -1.4

TROPICS
South Pacific Convergence Zone SPCZ is north of its normal location for
this time of the year, stretching across the Solomons to Samoa to near
Marquesas A Madden Julian Oscillation MJO of extra convection has
stalled over northern Australia, and is slowly making its way into the
Coral sea ... the sub tropical jet is deflected south of its norm and is
mostly taking extra moisture that is currently over north Australia
southeastwards to west of south island and filling the hydro lakes (spot
energy price in NZ has gone from extreme high to extreme low is a few
weeks).

SUBTROPICAL RIDGE: STR.
Two cells of High pressure come and go over eastern NZ this week 2-3 Jan
and 5-6 Jan maintaining a warm northerly flow over the North Island.

TASMAN SEA/ NZ AREA
Low is expected to form in Coral Sea on 3 Jan and go south along 160 E
by 6 Jan and deepen to 990 at 37S. Some other lows may form in Coral Sea
on 7 and 8 Jan . And there is a replacement trough (between highs)
crossing much of South Island of NZ on 4 Jan.


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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