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

01 April 2018

Bob Blog 1 April



Compiled Sun 1 April 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.

Weather trend over the last month.

Sea Surface temperature anomalies as at end of March may be seen at

The SST anomaly image is much the same as t beginning of March, it still shows cooler than normal seas along the equatorial East Pacific, but somewhat weaker.

The Tasman sea warm zone, which has been there since November and which has been breaking records, is still there.  Looks like it may prolong autumn over NZ.

And the Gulf Stream off the east coast of North America continues to stand out as being much warmer than normal; this extra heat has energized storms over the northeast of North America, bringing regular winter snow and floods to Boston. Looks like there are more to come.    

South Pacific Cyclones during March have started near Vanuatu area. HOLA wen t SE, LINDA went south, IRIS went SW and bounced off the jetstream and is now in the coral Sea. And the most recent, JOSIE, has brought killing rains to western Fiji and is expected to go SE then SSE.


The cyclones we have so far this season my be seen on  time line at .


To see how the annual weather cycle and the seasons are working out, take a look at the average isobar maps from

The low pressures over Europe has encourages cold easterly winds, and the above maps show that this anomaly stretches from Siberia to Boston.  Ouch.

The anomaly map shows that lows are likely to form in the Micronesia to Hawaii area.

The subtropical ridge over the South Pacific has stayed in much the same place and intensified, typical or early autumn.  The 1015hP (between blue and white) isobar now covers all of South Australia and Tasman Sea.   Isobars southwest of NZ are closer together, an indication that the westerly winds of the roaring 40s are intensifying.


The last 30 days of rainfall, and its anomaly, as seen at TRMM, are at

In the Pacific, the drier than normal zone along the equator is typical of a La Nina episode.



IRIS lost its upper clouds in a jetstream last week, but its lower circulation was able to hold together and was diverted northwards over warm Coral Sea.  It has rejuvenated, and the label IRIS is good enough to refer to this entity as it may re-intensify. It is expected to meander SW then NW this week but not expected to make landfall. It contains squally rain.


JOSIE has been bringing heavy rain to Fiji in the days leading into Easter and was named on Easter Saturday.  Its rain has brought a death toll of at least 2, and 3 missing in Fiji so

It is expected to travel SE and fade well to east of New Zealand.


JELAWAT formed over Micronesia during last week and is traveling NE into the North Pacific.

A comparison of the weekly rain map from last week with the previous week shows the path of the cyclones and some heavy rain north of Hawaii.  The “equinoctial convergence zone” between south-of-Galapagos and north-of-Marquesas is still there.  See



SPCZ=South Pacific Convergence zone.

The SPCZ is reforming on the back end of JOSIE, covering southern coral sea and northern Vanuatu /Fiji. with an arm extending to Southern Cooks.

Another tropical Low is likely to form over Vanuatu on Thursday/ Friday and follow JOSIE to south of Fiji during weekend of 7 and 8 April.


Subtropical ridge (STR)

HIGH over northern NZ today Sunday is expected to travel off to the east between 35 and 40S.  

New HIGH is expected to travel across southern New South Wales on Wednesday and stall in the central Tasman Sea for the remainder of the week.  This High should steer JOSIE clear of NZ.


Around Tasman Sea

Between those two Highs, a FRONT is expected to travel over South Island on Monday and fade over North Island on Tuesday.  A more intense front is expected to travel over NZ early next week around 9 and 10 April.


Panama to Galapagos /Marquesas

Today’s data is showing that the recent period of good winds for departing Panama is now expected to be replaced by light winds from around mid-week.   The coming period of light winds may last for a while, at least until end of next week.

The “equinoctial” convergence zone continues to straddle 5S from about 90W to 120W. Something to avoid.


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