Bob Blog

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.
Compiled Sunday 4 June 23

A review of weather of the past month

Here is a link to a YouTube clip giving an animated loop of the isobars and
streamlines in the South Pacific for the last month
https://youtu.be/ttafdMxypnY

May 2023 brought an end to a blocking high east of New Zealand and then a
series of lows travelling east across the South Pacific. The Highs were
brief, making for very few good opportunities for sailing form NZ/Australia
to the tropics. The low on 20May was measured on my baro in Palmerston North
as 979h.

Warm sea temperatures continue to spread westwards along the equator from
Peru.
Marine heat wave around NZ has shifted towards Chathams. Another marine heat
wave covers eastern North Atlantic

Subtropical ridges have shifted northwards. Now the Arctic has high rather
than low pressures
The anomaly pattern in the southern hemisphere is almost the reverse of last
month's. In particular, both Arctic and Antarctic have flipped from positive
to negative .
The subtropical ridge has now drifted to a mean position north of NZ.
The 1015 isobar on its northern side now stretches from Australia north
coast to Tongatapu.
The westerly flow in the 40s and 50s is increasing.

TROPICS

Cyclone MAWAR dropped to an estimated central pressure of 897 hPa and Cat5
to Ne pf Philippines sand then faded on its way to southern Japan. There are
now tropical depressions I both west and east of the Philippines, where
potential is high for development this week.

The MJO, a burst of extra energy in the tropics, has finished crossing the
Pacific and a period of relative quiet is expected for next few weeks.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The South Pacific Convergence zone is expected to stretch from northern
Coral Sea to northern Fiji and northern Tonga areas. Another weaker
convergence zone is lingering between Northern Cooks and north of Tuamotu
Islands. A trough is expected over Fiji on Tuesday going southeast and
developing into a low south of Niue late in the week. Avoid.

HIGHS and LOWS
Low L1 is the surface reflection of a cold pool aloft and as such is
expected to travel only slowly across and to the east of northern NZ this
week. Avoid.
High H1 in the south Tasman Se is expected to swing around southern NZ and
to east of Chathams. This feeds cold sir into the moisture of L1 , a good
recipe for snow making in the squashed isobars between L1 and H1 over
central NZ. Avoid.
Low 2 well to south of Tahiti tonight is expected to deepen with the arrival
of a cold southerly and then travel off to the east.
The gulf of Panama = Not recommended due convergence zone and SW winds.
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