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

11 January 2015

Bob Blog

Issued 11 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: extra heat has been stored in the Pacific Ocean for a while now
and all the Oceanic indices have crossed the threshold into 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 stuttering down and up again
over last few weeks.

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.

As mentioned in my Weathergram on 21 Dec, we have been in-between" MJO
cycles for the past few weeks. These MJO cycles of extra oomph are known to
activate the South Pacific Convergence Zone and sometimes here trigger
tropical depressions/cyclones.

Well, we now have an MJO cycle heading into the Coral Sea and towards the
180 line over the next week or so.

Indeed there are TWO tropical cyclone popping up in the Coral sea at present
as shown on the weather map from MetService NZ as seen on the Solomon
Islands Met web site at

Thanks to my friends in the Solomon Islands Met Service for keeping me
informed of their warnings.

These tropical depressions have been picked up by the computer models.
According to the GFS ensemble one (90P) is expected to travel to the
southeast across Vanuatu and then towards the zone between NZ and
Fiji/Tonga, and t other (91P) might go WSW then bounce off Aussie coast then
head east for zone SW of New Caledonia. If these tracks get close to you
then remain vigilant and seek updates as these tracks will likely change.

A low shown of the weather map near 3N 154E is a possible equatorial twin
for 90P. For more about equatorial twinning see

If you are a budding meteorologists looking for a topic for Masters or PhD,
then this could well be just right for you.
This feature has been picked up by the computer models as 92W and is
expected to travel WNW to Philippines then re-curve.

There is also a tropical depression in the Indian Ocean between Madagascar
and Mauritius and this one is expected to go SE and fade away.

The weekly rain maps over the past fortnight show that rain is increasing
all along the South Pacific Convergence Zone and, especially on both sides
of the equator near 155E, as well as NE tip of Australia and around

SPCZ=South Pacific Convergence zone.
SPCZ is expected to strengthen this week and split into two with one section
over Coral Sea, across Vanuatu and between Fiji and NZ, and the other
section across Southern cooks and stretching to southeast.

STR= Sub-tropical Ridge
A new High cell is expected to cross Tasman Sea on Mon/Tue and NZ on Wed.
Next High is expected to cross South Tasman Sea on Sun/Mon and South Island
on Tuesday/Wednesday 20/21 Jan.

Over NZ
A series of troughs should cross NZ from Thursday to Monday, progressing NE
across the country.

See my yotpak at for terms used.
Weathergram text only (and translator) is at
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