Bob Blog 5 March

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 5 Mar 2023


Here is a link to a YouTube clip giving an animated loop of the isobars and streamlines in the South Pacific for February 2023

Feb 2023 will be long remembered for Cyclone GABRIELLE (mid-month) over Norfolk Island and Te Ika o Maui / North Island. The South Pacific Convergence zone drifted south into the Coral Sea and formed GABRIELLE and JUDY (then KEVIN in early March).


12 Feb

Sea Surface temperature anomalies from


The cool waters of La Nina continue to relax. A marine heat wave continues to affect southern NZ, especially Fjordland, bleaching the coral there. There is also a marine heat wave around the Falklands. Since these hotspots are 180 deg longitude apart this suggests there may be a connection between them and stalling of atmospheric wave 4.

Indeed this has been studied and seems to be valid … See

Average isobars for past month (below)



The norther subtropical ridge has shifted north onto central Europe and intensified in the North Pacific. The southern hemisphere pattern is much the same as last month despite the daily drama. In February Canada is at its coldest and storm paths encourage snow/ice storms across USA but in 2023 there were two dramatic storms.

Pressure anomolies for past month (below)


The anomaly pattern also shows the shift and intensification of the northern subtropical ridge, as well as several subtle changes.

Zooming into the NZ area

Last month below



Previous month above

February has a very similar pattern to January, but the highs near Chatham Islands have been slightly weaker.


The positive boost of the MJO cycle that has been affecting the Western Pacific over past few weeks is expected to fade away over next two weeks allowing the South Pacific Convergence zone to return to normal.

The latest cyclone activity report is at and and Tropical Cyclone Potential is from


FREDDY reformed over the sea and is expected to make another landfall onto Mozambique this week. JUDY and KEVIV ploughed thru Vanuatu last week, and KEVIN is expected to sideswipe southern Tonga tonight.

The potential for development across the Coral Sea remains above normal, and something just may brew there next weekend.

It is expected to peak over Vanuatu on Tuesday and Wednesday this week and then go southeast and miss Aotearoa/NZ. Avoid.


Weather Zones Mid-week GFS model showing isobars, winds, waves (purple), rain (red), MT (Monsoonal trough), STR (Subtropical Ridge), SPCZ (South Pacific Convergence Zone) CZ (Convergence Zone) and CAPE (lime)


CAPE maps mid-week GFS and EC from Predictwind, showing chance of lightning.


Rain Accumulation next five days from


The SPCZ is expected to remain active from Solomons to Fiji and another convergence one is expected to remain active across Cook and Austral Islands. A tropical low may form in the Coral Sea at the end of the week.


TC KEVIN or L1 is expected to continue to the SE and remain this week as a large low well east of NZ. High H1 in the south Tasman Sea starts the week by feeding cooer SE winds onto NZ, and then travels slowly north across the country bringing a few sunny days, and then moves off to the east along 30S allowing a trough to reach NZ by Friday preceded by NW winds and followed by southerlies.

Mainly easterly winds across the north Tasman Sea this week should help voyages to the Brisbane area.


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