Bob blog 21 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 21 Feb

The Cause of the cold in Texas

Texas has been breaking many records for cold during the past week— Basically the polar jet stream has been weak and allowed a burst of polar air to break southwards as far as Texas.



The Arctic Oscillation index is a parameter that is positive when the polar vortex is well contained, and has spent much of the northern winter NEGATIVE with a big dive in early February



One reason for the blackouts is that the electricity grid could not cope with the increased demand. The cold weather froze natural gas wells and blocked pipes. It also froze some wind turbines, but the main problem was with natural gas which is the state’s primary energy source. The network engineers managed to stop a state-wide blackout by controlled overloading. Also, Texas has insisted on having its own grid and has little interconnection to the USA western or eastern interconnections. (Source:

The Tropics

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


TC DUJUAN is moving onto the Philippines and TC GUAMBE is tracking southeast from Mozambique channel.

There is a moderate potential for a Tropical Cyclone to form between Vanuatu and Samoa..


Weather Zones Mid-week GFS model showing isobars, winds, waves(magenta), Rain (Blue), STR (Subtropical Ridge), and SPCZ (South Pacific Convergence Zone).


Predict wind CAPE mid-week gives two possibilities for SPCZ.


SPCZ=South Pacific Convergence zone.

SPCZ is north of its normal position and from Papua New Guinea to Samoa/Southern Cooks

A tropical low over the Southern Cooks is expected to travel southeast and deepen in the subtropics from Monday to Wednesday local dates.

Another tropical low is expected to deepen near Vanuatu by Mon 1 March.


Rain Accumulation next five days from

Subtropical ridge (STR)

HIGH 1026 east of North Island is south of Tasmania on Monday is expected to travel across central Tasman Sea this week and onto central NZ on Friday/Saturday.

Next HIGH is expected to travel east across Tasmania on Wednesday and then go southeast around southern NZ on Thursday.

NZ/Tasman troughs

Low 990hpa between Coffs harbour and Lord Howe is travelling south-southeast and expected to zip past the south of the South Island on Wednesday.

Another Low is expected to form east of Eden by Friday and travel southeast past south end of NZ by Tuesday 2 March.

Panama to Galapagos/Marquesas

Good northerly winds for starters. There is likely to be a good tail current near EQ 85W, and a head current near 5-6N 85W so good idea to go direct, or if heading for Marquesas go via south of Galapagos.


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Published by metbob

Pattern and Chaos

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