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

15 January 2011

BOBGRAM7 issued 16 Jan 2011

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. .

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

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.

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.

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.
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