Weathergram 12 Aug 2012



Issued 12 August 2012

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 of weather maps, so please fine-tune to your place. Dates are in UTC unless otherwise stated.

The Ocean:  Seas surface temperature anomalies around the Galapagos continue to sneak above normal indicating we are on the verge of a new El Nino episode, but we are NOT there yet.

The Atmosphere: The Southern Oscillation Index or SOI is now dipping again. Its 30-day running mean rose during July from -1.21 to +0.27 and has dropped to -0.65 on 12th August. So the atmosphere is in neutral territory.

This dichotomy between atmosphere and ocean is leading to some unusual weather patterns.

Monsoon is entering the Western North pacific and continues to be more active than normal ,

Tropical cyclones:  Things were tragic last week in the NW Pacific with HAIKUI, and there are some other disturbances starting up in the region. There is also a new tropical Low spawning in the Atlantic and there are two disturbances off west coast of Mexico. Still busy.

In the South Pacific, the Convergence Zone SPCZ continues to be fairly quiet. There has been a weak CZ from Solomons to the southeast and this occasionally extends to Vanuatu or sometimes Fiji depending on passing mid-latitude lows and jet streams.  Water-vapour satellite imagery shows Australia to be a source of dry air that goes eastwards, evaporating a lot of tropical features. The main Convergence Zone CZ seems to be located between 5 and 10S from 175E to 160W. This is abnormal and is leading to some great opportunities to sail west from French Polynesia towards Tonga without being molested by the SPCZ for those seeking an easy passage. There is no guarantee this scenario will be around by the end of the month, but it looks good to go this week.



Map for GFS model for Wed 15 Aug oo00UTC with features given in text.(click to expand)


The STR is sticking to its northern latitude position along 20 to 30S and having a slowly intensifying time this week.

The Highs are expected to hug Australia until around Tue 21 Aug and after that one may venture into Tasman Sea.

One small cell should zip across the north Tasman sea on Thu 15/16 Aug and fade east of the dateline on Fri/sat/sun 17/18/19 Aug.

NZ/Tasman Sea

We continue with a procession of lows moving across the Pacific, without much opportunity for a high to fit in between them until mid-next week; this is a typical winter pattern.

The Low crossing NZ on Mon/Tue 13/14 Aug is likely to be followed by a disturbed westerly flow on Wed to Fri (15-16-17 Aug), then a prefrontal northwest flow on Sat 18 August and another low on Sun/Mon 19/20 Aug.

Traveling towards New Zealand this week:

If you can time it, then that wed to Sat gap is the best time this week to approach NZ.

The terms used are more fully explained in my Yacht Pack .

More info at and

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