Bob Blog 5 Jan 2020



Compiled Sun 05 Jan 2020

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.


Sea Surface temperature anomalies as at start of December compared with the start of January may be seen at

Late November (below)



Early January (above)

The main changes are in the Indian Ocean and South Pacific Ocean.

The Indian Ocean has gone more into an Indian Ocean Dipole positive mode. With cool temps in the east Indian Ocean (upwelling), and warm temps in the west, this deprives Australia of rain, so the outlook is for more bushfires there next month or longer until the rain returns. Around NZ there are warm seas in the west Tasman Sea and also, (reason unknown), well to east of NZ in the central South Pacific. This is an unusual pattern and is likely to produce some unusual weather in the next few weeks.

During December there have also been some small change in the pattern around South America, but anomolies in the North Pacific remain much the same.

To see how the annual weather cycle and the seasons are working out, we can check the average isobar maps for past 30 days and their anomaly from

Average isobars for November (below)



Average isobars for December 2019 (above)

The subtropical ridge in the southern hemisphere has shifted southwards. The area below 1010hPa in the equatorial area has expanded southwards, with a zone now over Northern Australia.

Pressure Anomalies November 2019 (below)



Pressure Anomalies December 2019 (above)

There remains Higher than normal air pressure over arctic and Antarctic and this is displacing cool air to mid- latitudes. Features have moved or rearranged in the Northern Hemisphere. Features in the Southern Hemisphere are in much the same position as last month, but are repositioning—-That high pressure zone over eastern Australia encourages anticyclones. And lower pressures about and south of NZ are encouraging SW winds.

Zooming into the NZ area, and comparing monthly anomalies from last month with now, shows that the subtropical ridge STR has strengthened and shifted southwards, but the 1010 isobar is still over central NZ .

We now have a SW anomaly flow over NZ . Finally, we have an easing /lowering in the anomoly pressures over Antarctica.




December (above)


The Tropics

The latest cyclone activity report is at and TCFP tropical Cyclone Formation Potential at


TC SARAI weakened over Tonga and Southern Cooks last week.

No named storms at present, but there is high potential for TC formation over N Australia this week, and some lower potential zones around PNG


Weather Zones (see text) as expected Wednesday 00UTC showing isobars, winds, waves(magenta) STR (green), and SPCZ (red). Pink area = lightning likely (high CAPE) .


Arrow  shows  main SW winds this  week over  NZ

SPCZ=South Pacific Convergence zone.

The SPCZ is snaking across the South pacific, from Coral Sea to north of Fiji to Southern Cooks, but is rather weak this week.

Ok to do some Island -hopping this week.


Accumulated rainfall for next week from

Subtropical ridge (STR)

HIGH in the north Tasman Sea is expected to fade across northern NZ quickly on Monday as a new high travels into the southern Tasman Sea. That new high is expected to stay put and get reinforced on Thursday , then travel east across central and northern NZ on Saturday.

Tasman Sea /NZ/Aus

Troughs travelling northeast across NZ on Monday, Wednesday night /Thursday and Sat/Sun maintain a mainly SW/S flow as far as 30S to north of NZ this week. Better wind and swell for getting from tropics to NZ from late this week

For Noumea to Aus: With a blocked High in the Tasman sea, should be OK with SE winds for this route until Friday, but may be showery for the weekend and strong SE winds early next week as a low possibly deepens over Coral Sea


If you would like more detail for your voyage, then check to see what I offer.

Or Facebook at /

Weathergram with graphics is at (subscribe/unsubscribe at bottom).

Weathergram archive (with translator) is at

Contact is or txt 6427 7762212


Published by metbob

Pattern and Chaos

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