Bob Blog 26 July

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 Sun 26 July 2020

Addendum to last week’s blog about barometer. There is a weather map on the web that shows the 1013.25 hPa . This shows how straight it is, dividing the places of higher pressure and lower pressure evenly. The map also has pink areas for rising pressure and blue areas for lower pressure, which you can check with your own barometer. It’s

New Cyclone model.

A new tropical cyclone forecasting model has the potential to save lives here and in the Pacific.

More time for communities to prepare is key, and the new outlook model will generate predictions for the number of tropical cyclones at an individual country level, up to four months before the start of the tropical cyclone season.


NIWA/STUFF.CO.NZ Niwa scientist Dr Andrew Lorrey

It has been developed by climate scientists from the University of Newcastle and the National Institute of Water and Atmospheric Research (NIWA), in New Zealand.

The new cyclone outlook model can detect increased cyclone activity and forecast cyclone activity months ahead of time, he said.

It’s also known that climate change will intensify the impact of cyclone seasons, and is making the events more and more common. However, at this stage, the Nov 2020 to May 2021 cyclone season is expected to be about to BELOW normal.


The Tropics

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

There are THREE active storms at present, HANNA is attacking inland Texas, DOUGLAS is brushing by Hawaii, and GONZALO is skirting the north coast of South America. There are several areas around or increased potential for cyclone development.



Weather Zones (see text) as expected Wednesday 00UTC showing isobars, winds, waves(magenta), Rain (Blue), CAPE (pink), STR, and SPCZ.)


What a difference a week can make o the weather map!

SPCZ=South Pacific Convergence zone.

This is likely to be about normal from Solomon Islands to north of Vanuatu to Tuvalu and Tokelau to Samoa an d then SE to French Polynesia

Passing trough – now near Cook Islands, moving onto French Polynesia mid-week

Next passing trough over New Caledonia on Wed/Thurs.


Accumulated rainfall for next week from

Subtropical ridge (STR)

HIGH 1030-1034hPa in central Tasman crossing central NZ on Mon and the traveling off to southeast from Tuesday but leaving behind stubborn ridge. There is expected to be a SQUASH zone on the northern side of this high, peaking with strong to possible gale ( in exposed places) SE winds near Tonga mainly Tues/wed.

New high 1028hPa expected in west central Tasman on Friday

Forget about crossing the Tasman Sea this week. A Low, forming off Coffs tonight is expected to go SOUTH and deepen to 986hPa off Sydney on Tuesday then SE to South Tasman by wed/Thu .

Another Low is expected to from north of first low in central Tasman Sea on wed and move SSE into South Tasman 994hPa for southern NZ by Friday

From Panama: ITCZ 10N to 7N, light winds maybe NW for starters but SW form 8S to 88W then S or light winds a round gala then a switch to S winds. Not sure what GANZALO will do.


If you would like more detail for your voyage, then check to see what I offer.

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Weathergram archive (with translator) is at

Contact is or txt 6427 7762212


Published by metbob

Pattern and Chaos

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