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

07 December 2014

Bob Blog

Issued 07 December 2014

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 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, relaxed for a while in October, and dived below -
10 early in early November, and is now hovering near -10.

We know that in an El Nino event the latitudes of the normal weather zones
are drawn closer to the equator, causing the South Pacific Convergence zone
to shift further north and east of its normal position.

Typhoon HAGUPIT is tonight moving NW across northern Philippines. Just over
a year and a month after HAIYAN.
Usually December is a quiet month for cyclones in the NW Pacific, however
another tropical system is expected to form near 5N 140E by Tuesday and
deepen as it passes near Yap on Wednesday/Thursday and then deepen further
until it is expected to visit northern Philippines next Sunday, one week
after HAGIPUT. However if this system takes a track similar to HAGIPUT then
it may encounter cooler conditions in the recently stirred surface waters
and thus not intensify as much. We hope.

Weekly rain maps over the past fortnight show an increase in convection over
the past week spreading eastwards from Indonesia to Micronesia. This
increase in convection is associated with what is called an MJO or Madden
Julian Oscillation, and has helped trigger and fire up HAGIPUT and may
trigger a few more tropical lows in the Micronesian area during the next two
This increase in convection may well gradually make its way into the Pacific
Ocean over the next few weeks. By mid-December this is expected to increases
the risk of a tropical cyclone generating in the area north of Vanuatu.

SPCZ=South Pacific Convergence zone.
SPCZ is expected to take a week off over PNG and Solomon Islands and be
strong from northern Vanuatu to Wallis/Futuna to Samoa to Southern Cooks.
>From the end of this week there is likely to be an increase in activity
around Australia and in the area about and north of Vanuatu.

STR= Sub-tropical Ridge
The STR has split into a strong zone well to the south from Aussie Bight
to south Tasman Sea, and a northern zone lingering at 30S between NZ and
The northern High is expected to slowly travel east to southeast between
30S and 35S as a low deepens between the Highs in the Tasman Sea by
Thursday local.

Over northern NZ
Brief ridge is expected to cross northern NZ on Monday with light winds,
followed by a N/NW flow on Tuesday to Friday (as low develops in Tasman
Sea) and then an associated front on Saturday, followed by a brief cool
southwest flow on Sunday 14 Dec, and then light winds in a ridge on
Monday 15 Dec.

See my yotpak at for terms used.
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