Bob Blog 6 June 2021

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.

Compiled Sunday 6 June

First some great news.

Max of has fixed the links to weather map images that are small enough to be able to be accessed when you are at sea by sending emails to even if you are using winlink on a UHF radio.

WeatherMap coming from Fiji Met Service:
–> 3AM FST Surface Map available daily from 05.00am Fiji time
–> 6AM FST Surface Map available daily from 09.30am Fiji time
–> 09AM FST Surface Map available daily from 11.00am Fiji time
–> 12PM FST Surface Map available daily from 03.00pm Fiji time
–> 03PM FST Surface Map available daily from 05.00pm Fiji time
–> 06PM FST Surface Map available daily from 08.30pm Fiji time
–> 12AM FST Surface Map available daily from 03.00am Fiji time

WeatherMap from New Zealand Met Service update every 6 hours, normally at 02-08-14-20 UTC TIME:
–> Last Analysis Pressure chart Actual time
–> +30 hours pressure forecast chart
–> +48 hours pressure forecast chart
–> +72 hours pressure forecast chart


Sea Surface temperature anomalies from


The only highlight of note is a warm blob in the 40 latitudes in the Northeast Pacifc. La Nina has gone, and eastern equatorial Pacific is now near normal.

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 past few weeks (below)


The subtropical ridges in both hemispheres have shifted north. It has intensified in the southern hemisphere and in North Pacific and North Atlantic but weakened over interior of Europe (as per normal). The north Indian low has got below 1010… the Indian monsoon has started in the past few days and is a few days late. The Antarctic High has intensified to over 1030.

Pressure anomolies for past few weeks (below)


A belt of high pressure has shifted from East Eurasia /North Pacific to cover north America. And across the north Atlantic toards Spain. A High/Lo couplet in the southeast Pacific has drifted westwards, bringing more easterly winds than normal to NZ.

Zooming into the NZ area

Last few weeks (below)



A month ago (above)

The subtropical ridge has sifted north as shown by the 1015 isobar. An interesting trough has formed in the Southern Ocean near 120. The intensification of the Antarctica high is probably due to the dark cold of winter.

The Tropics

The latest cyclone activity report is at and Tropical Cyclone Potential is from


In the past week TC BLANCA briefly formed off west of Mexico. There is still a moderate zone of potential development there, and a weak zone east of Philippines and in China sea.


Weather Zones Mid-week GFS model showing isobars, winds, waves(magenta), Rain (Blue),

STR (Subtropical Ridge), SPCZ (South Pacific Convergence Zone) and CAPE9 (in pink)


CAPE mid-week as seen by ECMWF and GFS from


SPCZ=South Pacific Convergence zone.

The SPCZ is expected to be rather thin and weak, stretching from Solomon Islands across Coral Sea to Samoa.

A passing trough is expected over Southern Cooks to French Polynesia next few days.

Another passing trough is expected over Tonga on local Tuesday reaching Southern Cooks by end of the week. and southern Cooks by end of the week.


Rain Accumulation next five days from

Subtropical ridge (STR)

HIGH over 1030 east of the South Island is lingering near 45S 170W until mid-week then travelling north to 30S and fading, and likely to be joined by another High near 45S by mid-week, then the combo travels off to the east along 40S.

No highs in the Tasman Sea this week. A good week for getting from Australia to Fiji.

Aussie/Tasman/NZ troughs

LOW has formed just north of Northland and is expected to linger there until mid-week.

Another low is expected to deepen offshore of Sydney by mid-week and move across central Tasman and reach central NZ early next week.

Another low is expected to form near 25S by end of the week in the passing trough over Southern Cooks.

Panama to Galapagos/Marquesas

Winds in Panama are expected to turn southerly this week, and the ITCZ is likely to visit. West to SW winds between Panama and Galapagos, with and east-going current. It’s the end of the season for sailing into the Pacific.


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