Bob Blog 25 Nov



Compiled Sun 25 Nov 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.

A friendly KIWI welcome to all the visiting yachts who have recently arrived in NZ.

When you are sailing around our cruising grounds you may wish to check out our coastal weather:

Where to get NZ weather

MetService has 18 Coastal areas and 11 Recreational areas and produces marine forecasts for these compiled by a dedicated team of specialized marine forecasters. These forecasts are updated four times daily and carry an outlook covering the following three days. They are available at,

or for your mobile at

or download the MetService Marine App: see more at

or via MetPhone at


If you have access to email when at sea the you can download the text of a coastal or recreational marine forecast by sending a email to, no subject needed, with message



where NAME is the name of your desired region (e.g: brett or bay-of-plenty or lake-taupo)


Marine Radio

Taupo Maritime runs ZLM radio HF/SSB/SW stations on 2207,4146,6224, 13356 and 16531 kHz in English

Maps are sent via Radio Fax on the following frequencies 3247.4, 5807. 9459. 13550.5,16340.1

Schedules are on the MetService website

NOWCASTING: New Zealand Coastguard Weather information (Nowcasting) is available via VHF for 15 places around the North Island and 5 places around the South Island.

See the map at

or download their app: see more at

Trip planning

A lot can be said about the usefulness of for checking if it may be good to go sailing over next few days.

During the past week one of my regular readers shared with me his blog on trip planning


Weather enthusiasts are always seeking new web sites for delving into the weather, and the best I have come across I heartily recommend is

In particular, when planning for the week ahead, check out

The weather geek site contain many weather treasures , have fun browsing.

El Nino:

The latest sea surface temperature map shows an anomaly of warmer than normal seas along the equator in the eastern equatorial Pacific. This anomaly is getting stronger and when it becomes strong enough the event is called an EL NINO.


SST as seen at

Now, as we move into December we can be reminded of the origins of the naming of this tropical anomaly as El Nino. The full title is “El Nino di Navidad” or the Christ Child of the nativity. It got this name because in Peru, once every few years, rain fell over the usually very dry interior. These rains arrive along with warmers seas along the Peru coast around Christmas time and so the event was named after the festival they were celebrating (Spanish is the leading language in Peru). In moderation the rains are a blessing, and the title seems fitting. But in the past few decades an El Nino brings flooding and landslides to Peru, It also makes the anchovies harder to catch, as these fish stay in the cooler waters, and in an El Nino the top of the ocean becomes coated with warmer seas from equatorial regions, so the anchovies go so deep they are out of reach.

This incoming El Nino is already showing itself in Peru:

NIWA have stated that this summer’s incoming El Nino is likely to behave differently from normal. The warmer seas along the equatorial Pacific that make up an El Nino normally occur near South America, but this year they seem to be occurring more towards the central Pacific. This is known as a central-based El Niño, or El Niño Modoki. Modoki is a Japanese word that means “same, but different”.


The unsettled weather we have been having during November is typical of an incoming El Nino. We can use this as an indicator that the coming months may bring the Bay of Islands more days with southwest winds than normal, but there will still be plenty days with sea breezes or with northeast winds. Maybe around a third each way.


Latest cyclone activity and TCFP tropical Cyclone Formation Potential as seen at


MAN-YI is heading towards Japan and is expected to peel off to the east of Japan.

USAGI is expected to make landfall near Ho-Chi-Minh city.

Looking at the weekly rain maps, last week’s shows the tracks of MAN-YI and USAGI, and also an intense buildup of convection along the equator near 140E, just north of PNG.

This is weakening at present, but the forecast is for a robust MJO event to move into the Pacific over the net two weeks, and that may indeed increase convections along the South Pacific Convergence zone.





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


SPCZ=South Pacific Convergence zone.

The SPCZ is expected to strengthen between Solomon Islands and north of Fiji this week. There may be a tropical low forming near Vanuatu next week in early December.

The convergence zone between Samoa and French Polynesia this week is expected to weaken away.


Accumulated rainfall for next week from CZ= convergence zone.

Subtropical ridge (STR)

The STR has been shifted to around 20 to 35S and is very weak. One small High is expected to travel eastwards from New Caledonia to south of Tonga from Tuesday to Friday this week.

Tropics to New Zealand

A series of trough and lows are continuing to cross NZ, with major lows over the North Island on Tuesday 27 and Sat 1 Dec this week. There should be an interlude of relative calm on local Thursday. Also, there should be more settled weather for arriving in NZ from Mon 3 Dec

Between Tropics and Australia.

Low from interior of Australia is expected to deepen as it moves into the Tasman Sea by around Thursday and then travel to northern NZ by Saturday. This offers opportunities for sailing from Australia to New Caledonia, but closes opportunities for sailing t’other way this week.

From Tahiti to Tonga

Looks OK with easterly winds, something light. However, there is expected to be a weak trough traveling east to south of 20S reaching Tongan area around wed UTC and then Southern Cooks area around Sat 1 Dec, with light variable winds.


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

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