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

26 July 2015

Bob Blog issued 26 July



Issued 26 July 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.


Prof Valentina Zharkova from the UK’s Northumbria University pointed out recently at a symposium in Wales that the recent low sunspot activity was pointing to a downward trend consistent with a longer-term beyond the 11-year cycle. “The model predicts that the magnetic wave pairs will become increasing offset during Solar Cycle 25, which peaks in 2022. Then during Cycle 26 (~2033) the two waves will become exactly out of synch, canceling each other out. This will cause a significant reduction in solar activity…. We predict that this will lead to the properties of a ‘Maunder minimum’ ”.

The ‘Maunder Minimum’ was a period of almost no sunspots between 1645 and 1715, It wasn’t long for the mainstream media to pick this up and come out with sensational headlines such as “Predictions from the model suggest that solar activity will fall by 60 per cent during the 2030s to conditions last seen during the ‘mini ice age’ ” (Royal Astronomical Society).

That 60% drop is referring to the fractional difference between the sun’s maximum and minimum output. In fact our sun, in spite of these ups and downs, has only varied by 0.1 per cent in its output during the past 2000 years. Some people are associated the ‘Maunder Minimum’ 1645-1715 with the mini ice age 1300-1870, but the mini-ice age started earlier, finished later, and is generally attributed to a period of volcanism on planet earth.

As Prof. James Renwick of Victoria University in Wellington explains “This effect is unlikely to bring on the type of cold conditions seen from 1645 to 1715. The big difference now is that there is a lot more greenhouse gas in the [Earth's] atmosphere than there was in the 1700s."

For a full review of the media miss-hype check out


Perhaps we should instead be devoting all this time and effort to something of more immediate importance, such as a study of the intensity of anticyclones – are they getting higher?

The anticyclone in the Tasman Sea mid last-week was large and had a central pressure of 1036 hPa.

This anticyclone is now east of NZ and the computer models are having a hard time dealing with it; they want to re-intensify it to over 1040 when it is south of French Polynesia by Wed 5 Aug, as seen at



Out west, HALOLA is now in its third week and a tropical depression near southwest of Japan.

There are a few tropical depressions around but the activity of the past two weeks now seems to be subsiding this week.


The year is turning: This week marks the start of the ‘dog days’ of the northern summer, when the northern continents normally get the hottest day of the year as the dog star Sirius rises just before dawn. Because it takes long clear nights to make a frosty mornings, we in New Zealand may already have had our coldest morning of the year (but our coldest day-time temperature also usually occur in late July/early August).


The weekly rain maps over the past two weeks show an increase in intensity in the convection across Tuvalu and Tokelau, also along the ITCZ, and a burst of activity in the Asian Monsoon.


Weekly rain signatures for past two weeks, are seen at




SPCZ this week is expected to stretch from south of Solomon Islands to Tuvalu to Tokelau to Northern Cooks. It is active at present (squally) and looks likely to cross the Bora Bora and Papeete region on local Tuesday (Wednesday UTC).  Avoid.

There is a possibility that a tropical depression may form near the Solomon Islands area late this week, with heavy rain and squalls. Sad to report.


STR= Sub-tropical Ridge

The High that was in the Tasman Sea mid last-week is now east of NZ travelling slowly east along 40 to 45S.

A new High is expected to move from inland Australia into Tasman Sea along 30S starting mid-week and cross northern NZ on Thursday and Friday. There is a squash zone of enhanced SE wind on the north side of this high and in the Coral Sea



A passing front on Monday and a trough of Tuesday then a decreasing SW flow on Wednesday. Light wind sin the passing High on Thursday and Friday. Then another front in the north on Saturday/Sunday.


Travelling Westward from French Polynesia:

Wait form the SPCZ to come and go, hopefully all on Tuesday local, and then there appears to be an OK voyage to the west for a week or so.


Departing from Australia to the tropics this week:

The squash zone on north side of that Tasman High makes Brisbane to Noumea very difficult for first part of the coming week. A trough moving into the Tasman early next week may offer the correct weather pattern for a while.


Departing from Northern NZ going north.

A departure on Thursday seems to have the best pattern for a trip northwards from northern NZ this week.


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