Bob McDavitt's ideas for sailing weather around the South pacific

25 January 2020

Bob blog 26 jan




Compiled Sun 26 Jan 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 subsolar point (Overhead sun)

Recently I’ve been noticing the reflection of the sun in satellite imagery across the South Pacific as in images from

This is the subsolar point or the latitude of the overhead sun or the solar declination.

AT this time of the year the subsolar point is in the southern tropics and drifting north , it will reach the equator at the equinox in March.


Here is a table of its values for later part of January. Each date is at 00 UTC ( close to local noon in the South Pacific , and a negative latitude indicates southern hemisphere.

Jan 17date (2020) -20degrees 53minutes 11.3seconds

Jan 18 -20:41:27.6

Jan 19 -20:29:20.3

Jan 20 -20:16:49.6

Jan 21 -20:03:56.0

Jan 22 -19:50:39.9

Jan 23 -19:37:01.5

Jan 24 -19:23:01.2

Jan 25 -19:08:39.4

Jan 26 -18:53:56.6

Jan 27 -18:38:53.0

Jan 28 -18:23:29.0

Jan 29 -18:07:45.2

Jan 30 -17:51:41.7

Jan 31 -17:35:19.1


The Tropics

The latest cyclone activity report is at and TCFP tropical Cyclone Formation Potential at

Cyclones DIANE and ESAMI are in the Indian Ocean and a tropical depression is located near Niue in the South Pacific, with a moderate potential of developing briefly into a tropical cyclone in next 12 hours. This system is expected to weaken from tomorrow.



SPCZ=South Pacific Convergence zone.

The SPCZ is slowly rebuilding in the Coral sea and northern-Vanuatu area this week. There is also a persistent convergence zone over southern Cooks extending to the east/southeast.

There is a tropical depression near Niue tonight, it may briefly become a cyclone, but is expected to travel slowly off the south then southwest and weaken from tomorrow.


Subtropical ridge (STR)

HIGH is expected to stall around /east of northern NZ for the coming week.

Another High in the Tasman sea today is expected to travel slowly around northern NZ by Wednesday.

A third high is expected to enter the central Tasman Sea on Thursday and then onto northern NZ by the weekend.


Tasman Sea /NZ/Aus

For Northern NZ: Remaining high and dry with light winds and sea breezes. Maybe a SW wind and some showers on Wednesday.

Foe the South Island: trough on Monday/Tuesday followed by a few days of SW wind s then another trough by the weekend.

As for Noumea to Australia: Mainly SE/E winds, then NE near Aus coast so OK.

As for Sydney to NZ: trough net few days, then looking Ok from Thursday but will need to go SE to get around a High.


From Panama to Galapagos/Marquesas:

Northerly winds to around 4N. Then an active ITCZ and SW winds from 4N to 2N (will need some waypoints), then S /SE winds as far as Galapagos area, As for getting to Marquesas, not enough data for entire voyage but what data we have is looking OK .



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