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

25 January 2015

Bob Blog

Issued 25 January 2015
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.

The Ocean: The extra heat that has been stored in the eastern equatorial
Pacific Ocean is now decreasing and no longer pointing to an El Nino

The Atmosphere: The Southern Oscillation Index SOI (30 day running mean)
sums up the weather pattern over the South Pacific as one number. It is
based on the standardized difference in the barometer readings between
Tahiti and Darwin. It has been negative since July and dived below -10
(Australian units) for much of September, and again for a week in November,
then relaxed in early December, and has been up and down over past few

The Australian Bureau of Met have now wound down their El Nino outlook to
NEUTRAL for the next few months They are expecting the current episode to
now enter a decay phase. See

The recent new moon phase arrived within a few days of the moon's perigee
and the resulting king tides, combined with some heavy swells, managed to
bring sea inundation to Majuro and to some of the northern islands in the
Solomons group. The spring tides in January and February get extra oomph
from the warm seas in this area and sea inundation seems to be becoming an
annual January/February event. See

Cyclone NIKO took a brief visit to French Polynesia last Wednesday/Thursday
(local dates). The first named system of the year for the South Pacific.
Interesting how quickly it blossomed, but it was a small one.

A new MJO cycle is now starting in the Indian Ocean. There are no tropical
cyclones around at present but some small depressions in the mid Indian
Ocean may deepen later this week.

Extending the MJO cycle seems to have it moving into the Coral Sea area
around mid-February.

The weekly rain maps over the past fortnight show that the rain associated
with NIKO and the South Pacific Convergence zone during last week was the
most intense of the planet.

SPCZ=South Pacific Convergence zone.
SPCZ is expected to be strong this week from Tuvalu to Samoa to Northern
Cooks with strong westerly winds on its northern side. There is a risk that
a low may form on it near Samoa on local Thursday and Friday UTC and then
move to Niue area by Sunday UTC /Saturday local.

STR= Sub-tropical Ridge
The STR is well south of normal at present. The large HIGH east of NZ by
Monday is expected to only slowly travel east along 45S and should fade near
160W from Thursday.
A replacement High cell should squirt quickly across the south Tasman Sea on
Friday and build east of South Island on Saturday, then travel NE to 40S
then east along 40S next week.
The next HIGH should cross the central Tasman Sea at a more northern
latitude of 35S from Tues 3 Feb.

Over NZ/Tasman:
The NZ/Tasman area is NORTH of the STR this week, thus dominated by easterly
A weak trough is expected to fade in the north Tasman Sea near 160E with NE
winds on its eastern side and SE winds on its western side.
An interesting LOW near 35S 165W tonight is expected to travel westwards
towards Northland this week, reaching Northland on Thursday and Friday. This
system is caught in some easterly winds aloft, hence its strange track.
However the system is expected to weaken away nevertheless it does have some
strong SE winds and 3 metre easterly swells on its western side, especially
on Tuesday and Wednesday (local).
On Thursday, a LOW is likely to form in mid Tasman Sea, east of Tasmania.
This should then cross the South Island on Saturday/Sunday, and bring a
front/SW change to North Island on Monday/Tuesday 2/3 Feb, finally bringing
some welcome rain.

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