Bob Blog 5 Feb

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 05-Feb 2023

REVIEW OF THE LAST MONTH (January 2023)
Here is a link to a YouTube clip giving an animated loop of the isobars and
streamlines in the South pacific at

https://youtu.be/7EQXqv6h9J4

Lots of lows formed in the Tasman Sea. And Highs lingered between the South
Island and South of Tahiti. This fed a flow of tropical air from Tonga
towards NZ, as seen in Cyclone HALE on 11 Jan and the event that squeezed
torrential rain out from a line of thunderstorms on 27 Jan.


Sea Surface temperature anomalies can be seen at
psl.noaa.gov/map/clim/sst.shtml
The cool waters of La Nina continue to relax. A severe marine heat wave is
affecting southern NZ, especially Fjordland, bleaching the coral there. This
is starting to show signs of relaxing, see
https://www.moanaproject.org/marine-heatwave-forecast.
There is also a marine heat wave around the Falklands.

Average isobars for past month (below)
In the north Atlantic, west of Spain there has been a swap in pressure
systems from lows to highs. Elsewhere, January's pattern has been an
extension of December's.

Pressure anomolies for past month (below)
The anomaly pattern is much the same as in December, but Lows in the Tasman
Sea in January have been more intense than in December.

Zooming into the NZ area
January has a very similar pattern to December, but the highs near Chatham
Islands have been 5 hPa stronger, and that is what has accentuated the
tropical northerly flow from Tonga to Northern NZ.

TROPICS
There is potential this week for cyclone formation between the south of
Indonesia and the Coral sea.

WEATHER ZONES
South Pacific Convergence Zone SPCZ
The SPCZ is expected to be very active across the Coral Sea /New
Caledonia/Fiji and Tonga .
Tonight the SPCZ has a Low L2 south of Niue and this is expected to travel
off to the south-southeast. There is another Low L3 near Vanuatu, and this
is expected to drift southwest and intensify in the Coral sea next few days
and has the potential to then become a tropical cyclone and travel southeast
towards Norfolk Island/northern NZ this weekend. AVOID.
Low L1 (crossing the south Tasman Sea tonight) is a kicker and has
sufficient eastwards momentum to finally push the quasi stationary High (now
near Chathams Islands) off to the east. This may help trigger a pattern
change in the Southern Ocean, allowing another High H2 to travel east across
NZ on Thursday and Friday this week.

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