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

04 March 2018

Bob Blog 4 March

Compiled Sun 04 March 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.

For those who like to plan their voyages across the ocean well in advance, and decide to the nearest month when to reach where, according to the averaged weather, I recommend the NEW edition of Jimmy Cornell's "Ocean Atlas". JC has updated his popular atlas and sent me a demo copy as he asked me to review the South Pacific part. See
I particularly liked the detail that has gone into the pilot charts, and the text on various matters such as weather and currents... and an interesting chapter about the various names for the winds around the world. The passage maps make this a valuable primary resource for all cruising sailors.
Weather trend over the last month.
Sea Surface temperature anomalies as at 1st March may be seen at

The SST anomaly image still shows cooler than normal seas along the equatorial east pacific, but these are less than last month. So this La Nina is started to fade away in the Ocean.
The Tasman sea warm zone has been there since November and gave us our warmest ever measured summer. It too is starting to weaken. Cyclones during February have stirring the surface layer of the sea and mixed it with cooler temperature from underneath. This zone is still flecked with red spots as is much of the 40S latitude in the southern hemisphere. Interesting.
And the Gulf Stream off the east coast of North America is standing out as being much warmer than normal, this extra heat should energize storms over the northeast of North America.
To see how the annual weather cycle and the seasons are working out, check the average isobars for past 30 days and their anomaly isobar maps from

The "beast from the east" has only been active for the past week and doesn't stand oy=ut in these 30-day averages.
The subtropical ridge over the South Pacific is still in place much as it was in January. The 1010hP (between light and dark blue) isobar has shifted north onto southern NZ, indicating that the northward seasonal shift of the subtropical ridge is already happening, and NZ should see the return of South/Southwest winds penetrating further north during March.
The last 30 days of rainfall, and its anomaly, is seen at TRMM at

In the Pacific, both the ITCZ has an average position last month further AWAY FROM the equator than normal. This is typical of La NINA. Interestingly, the South Pacific convergence zone is somewhat north of normal (except where GITA visited Tonga, and tropical lows drenched southern parts of French Polynesia). In the Atlantic, the ITCZ is closer to the equator than normal.
TC DUMAZILE has formed in the Indian Ocean, indicating that a new pulse of MJO energy is forming there. It is off the east cat of Madagascar and expected to go southeast into the mid-latitudes and its remnants may reach 50S/Port-aux-Francais.

There is a tropical low between Fiji and Vanuatu. Some models have it deepening when it travels southwest towards Erromango/Tanna in southern Vanuatu on Wednesday/Thursday, and then recurving and travelling quickly southeastwards to east of NZ by late Saturday/Sunday 10/11 March.
To keep an eye on this feature follow Fiji Met Service at
Looking at the weekly rain maps from last week as at and the week before, we can see an increase in the intensity of the rain around Fiji to Niue, and in the ITCZ across the Pacific.
Around northern Australia, the monsoonal rain is continuing.

This week is the thirtieth anniversary of Cyclone BOLA affecting New Zealand in March 1988. It hovered off to the north of NZ for three days when the moist eastly winds on its south side hammered our Gisborne coast. It was held there by a large HIGH east of NZ. It seemed to hold onto a Cyclone category according to the Saffir-Simpson scale until it got south to around 42S (As seen at Wiki Project TC tracks at ---- but really, as soon as it left the tropics it transited into a mid-latitude depression - We dropped the word "tropical" and kept referring to it as "Cyclone Bola" to help the broadcasting media deliver the severity of the weather forecast to those at the receiving end.
As seen at
I was one of the lead forecasters on duty at the time. I can remember that we allowed TV reporters to do live interviews from our forecast room, maybe for the first time?.

SPCZ=South Pacific Convergence zone.
The SPCZ is expected to strengthen this week and a pulse of convection is likely to travel southwards with that tropical low as it moves to Vanuatu and then Southeast to east of NZ.
However, the rain accumulation map at suggests that this pulse of convection may weaken a lot as it leaves the tropics.

Subtropical ridge (STR)
HIGH to east of NZ was unbudging last week but is moving is expected to move off to the east this week. It would have been interesting if that low from Vanuatu had formed last week--- its trip to the southeast would've been blocked and it may have taken a path like Bola. However, Bola had more moisture to start with.
Next HIGH is expected to form east of Tasmania on Tuesday and travel across southern NZ on Saturday and then weaken over the North Island on Sunday, helping to direct the low from the tropics harmlessly off to east of North Island.

Around Tasman Sea
Trough over the North Island on Monday. Front reaching the South Island on Monday is expected to be drawn to the northeast on Tuesday and deepen into a secondary Low northeast of North Island on Thursday and Friday. There may be strong winds around the south and west sides of that secondary low.

Panama to Galapagos /Marquesas
Looks Ok to depart Panama from Monday to Thursday this week, after that the voyage may encounter a longer than normal period of light winds from 80W to 110W, and it may be better to wait until mid-next-week.

The cold air that reached Britain last week had been dislodged from the Arctic circle by an freak heat wave in the Arctic circle. See
If you would like more detail for your voyage, then check to see what I offer.
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