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

06 September 2015

Bob Blog 6 Sep 2015



Issued 6 September 2015

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.


Weather anomalies in August as seen at

and at show there was a  very strong sub-tropical ridge over the Australian bight and to south and east of NZ, with increasing intensity in the troughy conditions across the tropical North pacific (around 5 cyclones

in 4 weeks) and also over Tahiti to Cape Horn.   Typical El Nino conditions are solidly in place. 

The troughy conditions that were over Solomon Islands have shifted east towards Tuvalu.  There are slight above normal pressures over most of Asia showing a stuttering Monsoon, but Myanmar/Burma stands out as lower than normal pressures and has had floods and landslides last month killing over 100 and affecting over one million people.


Outgoing Longwave radiation OLR is a parameter that can easily be measured by satellites.  It is inversely proportional to cloud cover (OLR is highest over clear skies) So blue readings in the map correspond to bubbly clouds and yellow /red readings are mellow /quiet/cloud free areas.

From we can see that maps of last month’s OLR readings show that convection has been strong in the equatorial and tropical north pacific.

There was a period in early August of strong convection over Solomon Islands, and then rather quiet convection in the South pacific during mid and late August.



There are five tropical cyclones at present FRED is located in mid North Atlantic and weakening:

GRACE is to the SE of FRED and heading for Dominica in the Caribbean Islands.

KEVIN is off the Mexican west  coast

JIMENA is to the north of Hawaii:

And KILO is to the NW of Hawaii, heading for the Japan area The weekly rain maps over the past two weeks as seen at

show a weakening in the rainfall in the South pacific during the past week.



SPCZ=South Pacific Convergence zone.

Nothing organised at present.  Main band extends from Solomons area to northwest of Fiji and is expected to travel south this week and visit Vanuatu by Saturday and Fiji on Sunday/Monday and maybe Tonga on Tuesday

15 Sep local.  Minor branch between Tuvalu and Tokelau is expected to be strongest around local Thursday 10 Sep. Avoid.


STR= Sub-tropical Ridge

The HIGH that is in the Tasman Sea on Sunday 6 UTC is expected to travel east along 30S, crossing northern NZ on Tuesday. It is a weak HIGH and does not have a squash zone on its northern side.

Next HIGH (now crossing South Australia) is likely to be more intense and move into the Tasman Sea on Thu 10 UTC, then travel rather slowly NE,

crossing northern NZ on Wed 16 Sep UTC.  

This HIGH is likely to have a squash zone of strong SE winds on its northern side in the Coral Sea from Friday to Sunday.

Such a slow-moving HIGH offers a good opportunities for sailing to/from NZ/Australia or across the Tasman Sea in quiet conditions.  This may be the last such opportunity for a few months, as El Nino conditions often bring strong SW winds to the Tasman Sea area especially during Sep to November.



The Low we had over last weekend is still intensifying to SE of NZ on Monday, affecting Chatham Islands.

Tuesday is expected to be the day this week with sunshine and light winds,  but a frosty start in many inland places.

On Wednesday a LOW is expected to form in mid-Tasman Sea.  This is expected to intensify as it crosses NZ on Thursday along with strong northerly winds, and further deepen to east of the North Island on Friday/Saturday/Sunday—a typical event sometimes called an “olde man Southerly’ lasting three days and bringing intense rainfall to eastern North Island.


See my yotpak at for terms used.

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