Bob Blog 30 April

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 30 April 2023

A review of April weather
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 youtu.be/xgrzRC1Kbl8
April 2023 brought a mix of mobile lows and highs, along with a blocking
HIGH over Chathams late in the month feeding at atmospheric river onto
northern NZ.

The sea temperature continues to rise off Peru and the marine heatwave
around Tasmania to Chathams is relaxing. Seas have warmed north and south of
New Guinea. Little change elsewhere.

Average isobars for past month (below)
The greatest repositioning is happening over the Arctic with systems
relaxing, and the Antarctic with systems intensifying. The subtropical
ridges have shifted north.

Pressure anomolies for past month (below)
The anomaly pattern shows intense ridging over the Arctic and most of the
Antarctic.

Zooming into the NZ area
The subtropical ridge is drifting north over Australia and stronger in the
Indian Ocean.
The westerly flow in the 40s and 50s is lighter than normal south 0f New
Zealand.

TROPICS
All quiet on planet earth

WEATHER ZONES
The South Pacific Convergence zone SPCZ is expected to be well marked from
Solomon Islands to Samoa to Austral Islands and then with a tail to the
southeast.

HIGHS and LOWS
A BFH (big fat High) H1 is lingering over Chatham Island and should move
slowly east, with peak of 1039 hPa mid-week and with a squash zone on its
northern side between 18 and 25S.
Low L1 below 1000A in Tasman Sea west of Auckland tonight is travelling
quickly southwards and should move south of Southland on Tuesday.
Another low L2 is expected to cross Tasmania mid-week and stall near
Northland this weekend, finally followed by SW winds early next week,
perhaps.

Panama to Marquesas: There might be a period of northerly winds in Panama
gulf for starters mid-week. ITCZ is active to 2North. Doldrum of light winds
extends to 2South.

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