Bob Blog 8 March 2020



Compiled Sun 08 March 2020

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.


The Madden Julian Oscillation is a burst of extra convection that can trigger cyclones. It visits the South Pacific for around 10 to 20 days once every 4 to 6 weeks.

One way of showing a passing MJO is to look at the forecast for OLR or outgoing longwave radiation. When the tropical convergence zones are active the sky is full of cloud and this blocks the outgoing radiation from getting away to outer space, so OLR is low and coloured blue (for bubbly). When skies are clear radiation can escape to outer space and OLR is high, and coloured orange or (mellow) yellow.

A constructed analogue forecast of future values of the OLR, using the MJO, show that we are expected to have a phase of low OLR (blue values) over the next few weeks, and that means an active South Pacific convergence zone and increased cyclone risk gradually spreading east.


As seen at


The Tropics

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


There is an increasing risk of Cyclone formation in the northern Australia to Coral Sea region this week.


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



SPCZ=South Pacific Convergence zone.

The SPCZ is expected to become more active in the Coral Sea and stay much the same from Tuvalu to Tokelau to Fiji to Southern Cooks.

A tropical low is expected to form over Gulf of Carpentaria by Wed and move into the north Coral Sea by Saturday. Another Tropical Low may form in the Coral Sea by Friday and move onto New Caledonia this weekend. These lows may become tropical cyclones and should move ESE.

There is an increasing risk for more tropical cyclones in the coming fortnight.


Accumulated rainfall for next week from (isobars are for Sunday night).

Subtropical ridge (STR)

HIGH east of NZ is expected to fade on Monday.

High moving across Tasmania on Tuesday is expected to travel along 40S across the Tasman Sea and then stall near NZ on sat.

Tasman Sea /NZ/Aus

Trough crossing NZ on Monday followed by a southerly flow on Tuesday.

Another trough/Low may form NE of NZ by Thursday and travel SW onto northern NZ on Friday 13th and then move off to the SE.

Another trough is expected to cross Tasmania on Friday and then move into the Tasman Sea this weekend.

As for Noumea to Australia. This may well be affected by a tropical cyclone in Coral sea.

As for sailing east across the Tasman: it may be possible south of 35S after trough with a Wednesday or Thursday departure, so long as possible cyclone in Coral Sea follows its forecast.

From Panama to Galapagos/Marquesas:

North to northeast winds to 5N this week, then a good current and light winds to Galapagos.

To get to Marquesas this week shows that SOUTH of Galapagos is now the way to go (the winds north of Galapagos are expected to become light an d occasional westerly this week)

The ITCZ has a gap in it between 89W and 79W but does bloom at times just north of Galapagos.


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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