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

02 August 2015

BOB Blog 2 Aug



Issued 2 August 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.


30 day anomaly map may be seen at

This shows that weather anomalies remained the same throughout July as they were in June, with a very strong sub-tropical ridge over Australia, Tasman Sea /NZ, and troughy conditions over Solomon Islands and Tahiti.  Lower than normal pressures across the North Pacific vaguely tie in with the large number of tropical depressions and cyclones there last month.

The 30 day anomaly map for 1 Aug shows not much of a signal over Asia, and indeed this year’s Asian monsoon has been progressing in a stuttering fashion.

Indian Monsoon index is seen at

SOI (the atmosphere)

The SOI (Southern Oscillation Index) measures the (normalized) air pressure difference between Tahiti and Darwin.   With Darwin having higher than normal pressures, and the preponderance of Tahitian troughs, it is no surprise that SOI has been so negative lately.

SOI may be seen at

This current El Nino is expected to intensify until around November and then weaken, but it is not expected to drop below its current strength until around March 2016 , as shown at a figure from the International Research Institute (IRI) for Climate and Society (updated 14 July 2015).


There are two tropical cyclones at present GUILLERMO is Hurricane force and heading to affect northern part of Hawaii later this week; by then it is expected to weaken to storm force.

 And SOUDELOR is heading for Taiwan

The weekly rain maps over the past two weeks show the intense rainfall from these tropical cyclones, and even more intense and widespread rainfall from a tropical depression near east end of Solomons Islands.

Weekly rain signatures for past two weeks, may be seen at



SPCZ=South Pacific Convergence zone.

Depression to NW of Fiji is 01F and is expected to travel south between Fiji and Vanuatu then SSE to reach Kermadecs by Friday.  It may intensity on Monday and then weaken. It is worthwhile avoiding.  Associated trough should travel across Tonga on local Friday and early Saturday.

SPCZ this week is expected remain from Samoa to near the Tahiti area.  Moisture traveling along the SPCZ helped form a deep Low at 35S to south of French Polynesia over the last few days,  and this is expected to travel off to the east this week, and another Low is expected to form near 30S to south of French Polynesia later this week and travel off to the SE.


STR= Sub-tropical Ridge

The HIGH that was over northern NZ over the last few days has reduced to a ridge that extends to a High in the southern ocean and this ridge is expected to travel east along 30S this week to east of NZ.

Next high from Australia is not due in the Tasman Sea until Sat or Sunday 8/9 Aug.


One front is expected to cross South Island on Monday and North Island on Tuesday/Wednesday.  The next is expected to be more intense, connected to a Low below 980 hPa in the southern Ocean, and is expected to cross the South Island on Wednesday and the North Island on Thursday.  And then a cold and squally front associated with another low below 980 is expected to cross the South island on Friday and the North Island on Saturday.

Departing from Australia/NZ to the tropics this week:

>From Wednesday the swells over the Tasman Sea and to north of NZ are expected to be over 3 metres (and up to 6 or 7 metres) so it is more comfortable to stay put.


See my yotpak at for terms used.

See my website for information on tailor-made voyage forecasts– Feedback to

Tell anyone you like that to subscribe they should email me.

Weathergram text only (and translator) is at

Weathergram with graphics is at, click FOLLOW at bottom right to subscribe.

To unsubscribe send a reply email saying LEAVE.



1 comment:

Majid Vijah said...
This comment has been removed by a blog administrator.

Blog Archive