Bob Blog 1 July 2018n



Compiled Sun 01 July 2018

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.


Sea Surface temperature anomalies as at end of June may be seen at


As has been the case for a few years now, the warm anomalies outweigh the cool, so there is a net discontinuity in our oceans. The eastern equatorial Pacific is the focal region for ENSO and is now on a slowly warming trend. Temperatures around Australia and into the Tasman Sea are about to below normal, a possible indicator of drier than normal conditions in the next month or so.

The Gulf Stream off the east coast of North America still stands out as warmer than normal.

Warm anomalies continue in the north Pacific indicate a busy cyclone season for next few months.

To see how the annual weather cycle and the seasons are working out, here is a quick look at the average isobar maps from

Average isobars for past 30 days and their anomaly for JUNE


The isobar maps show that subtropical ridge in the southern hemisphere is looking robust. The North Atlantic and Northeast Pacific HIGHS are looking less strong than this time last month. The June Lows in the Tasman Sea have been less than the May Lows.

Polar westerly winds are stronger around Antarctica from NZ to South America but weaker than normal from South America to South Africa and around Australia to New Zealand. It’s complicated.

Zooming into the NZ area, the 1015hP (between blue and white) isobar has stayed put in the tropics and travelled east across NZ. It’s subtle, but observable. This indicates a change from a westerly flow to a (cooler) SW flow:


JUNE clip_image008

The last 30 days of rainfall, and its anomaly, as seen at TRMM at


The rain map shows extra convergence in the ITCZ from Bangladesh to Philippines , across s the North Pacific Ocean, around the Mexican west Coast and across the equatorial Atlantic, but it has been drier than normal over the Caribbean..

In the Southern Hemisphere there are large dry regions: Around Madagascar/ Western Indian Ocean, Vanuatu to Southern Cooks (the normal position of the South pacific Convergence zone), and the Amazon.

The Indian Monsoon 2018 arrived faster and earlier than normal, as seen at




Tonight, we have a TC off the west of Mexico (FABIO) and in the China Sea (PRAPIROON). Also, the remains of EMILIA are travelling to the NW, leading the way for FABIO.

If we compare thw past week’s rain with the previous week we can see that the intensity of the rain in the South Pacific Convergence Zone and around central America is intensifying.



– see



Weather Zones (see text) as expected Wednesday 00UTC showing isobars, winds, sea (magenta). STR, and SPCZ. Pink area = lightning likely (high CAPE)

SPCZ=South Pacific Convergence zone.

The SPCZ is expected to stay put from northern Coral Sea /Solomon Islands to northern Vanuatu, to Samoa to Southern Cooks. A small low should form on the SE end of the SPCZ, to SE of southern Cooks, on Tuesday 3 July UTC and deepen as it gets further SE.

And a small but rather intense passing trough/tropical low os expected to form over Wallis/Futuna are on Thu/Fri UTC and travel over Vava’u are on Fri UTC and Niue/Southern Cooks area on Sat UTC. Avoid.


Accumulated rainfall for next week from

Subtropical ridge (STR)

New HIGH is expected to spread into the Tasman sea on Mon/Tue and then travel NE across northern NZ on Wed/Thu and further NE next weekend.

Around Tasman Sea, NZ to tropics.

Looks Ok for a voyage for NZ to tropics any day this week.

Small low is expected to form off Queensland coat on Monday and fade in situ by Thursday. Strong disturbed westerly flow is expected to spread east from Tasmania/southern New Wales from Wednesday, reaching South Island of NZ by Friday.

TROUGH that crossed NZ on Sunday is expected to deepen into a LOW over Chatham Islands on Monday UTC that is expected to go NE on Tuesday/Wednesday UTC and then east/southeast. Avoid this Low.


Australia to tropics

Not this week, too much head wind. But an opportunity may be appearing around Sat 7 July.

Tahiti to Tonga

A dose of strong SE winds is expected to affect northern parts of this area on Monday and Tuesday UTC. And on Fri/Sat UTC a small but intense low/passing trough is expected to affect the Vava’u to Niue area. Next week may be better.

Galapagos to Marquess

Se to E winds, mostly less than 20 knots. To use available currents, go to 2S 95W and then 5S 120W and then direct.


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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