SOUTH PACIFIC WEATHER INFORMATION

Sandy and Sidney Van Zandt

(Sandy (call sign N1EIL) and Sidney, whose home base is in Connecticut, are cruising longterm aboard their 39ft cutter Sequel.)

We left Fort Lauderdale in December 1990, cruising through the Bahamas and on to Panama where we transited the Canal in March 1991. We crossed the South Pacific by way of the Galapagos, French Polynesia, Tonga and Fiji, and then sailed on to Opua in New Zealand's Bay of Islands, arriving in November 1991. There we spent the 91/92 cyclone season, and after a very enjoyable `summer' we left New Zealand in late May and headed back to Fiji. We are currently (September 1992) in New Caledonia and expect to be heading for the southern Queensland coast of Australia about mid-October.

The myth of steady south-east trade winds all the way across the Pacific is great for dreams, but is quite far from reality. We have had lots of good sailing out here in the Pacific, but we have had to utilize available weather information and a fair amount of good luck. In actuality, the factors that one deals with are:

1. Doldrums

2. Lows and Highs moving eastward across the Pacific from Australia, the Tasman Sea, and New Zealand where the lows often intensify

3. Reinforced or augmented trade winds

4. The South Pacific Convergence Zone and its interaction with cold fronts and troughs which develop.

Dealing with the doldrums (the Inter-Tropical Convergence Zone or ITCZ) is pretty well described in various sources on passage planning. We waited in the Las Perles Islands in the Gulf of Panama until the ITCZ moved north and then left for the Galapagos (short wait and fast passage).

Regarding the location and intensity of the South Pacific Highs, the closer the spacing of the isobars and the further north they are, the more the trades are reinforced. We might have 10 to 20 knots when the Highs were weak, further south and somewhat stationery, but experienced 25 to 35 knots or more when a High was strong and further north. Between 5S and 10S we did not feel very much `reinforcement' of the trades.

As we moved south of 10S we became aware that our `trades' sometimes shifted from south-east to east to north-east, gradually getting lighter and then often dying out altogether by the time the wind got to the north. It didn't take long to relate this phenomenon to the passage of a cold front further south, though for many of us who have lived in the Northern Hemisphere and are accustomed to the veering of wind during the cycle of a frontal passage it takes a while to begin thinking in terms of the mirror image patter of the Southern Hemisphere. A diagram taped at our nav station as a constant reminder helped in the transition.

When we reached the Tuamotus (15S to 17°S) we found the passage of these fronts was a regular occurrence. The wind would go into the south-west after the frontal passage, blow hard, and then gradually back south and south-east, giving us reinforced trades as a strong High filled in. Not liking to motor we often took advantage of these, and had some very quick but rough passages. We had three reefs in the main and very reduced headsails for seven of the nine days during the 1300 miles from Bora Bora to Tonga.

The South Pacific Convergence Zone was something we had never heard of before we got to the Pacific. (It is not to be confused with the ITCZ, or doldrums). In the winter it is a convergence which starts up around the Solomons (5°S 155°E) and stretches east-south-east to about Tahiti (20°S 150°W). It wanders roughly along that line but is constantly in motion, often causing real problems when it is very active and/or when a cold front or trough interacts with it.

In August and September 1991 violent conditions affected boats on two occasions that we heard of. Four boats westbound from Bora Bora a day after we had left in early August ran into 70 knots, sustained for four hours, and one boat registered over 100 knots during the worst of it. She was rolled to 135° after the seas built up, took a lot of water, and suffered considerable damage. Her crew pulled things together and made it to Tonga a few days after we did, where they were able to affect more permanent repairs. In Bora Bora winds over 60 knots were registered, and five boats ended up on the beaches or reefs during the mayhem. (Many anchorages there are very deep - 80 to 90ft - with questionable holding).

The second incident occurred north of Vava'u in Tonga. Four boats were enjoying a night sail in a pleasant 12 knot breeze from the north-east when they ran into 70 knots from the south-west in a matter of moments. In both cases there was no forecast to indicate this sort of weather approaching. Looking into it, however, I found that the boats were very near the forecast position of the South Pacific Convergence Zone.

In the first case (near Bora Bora) there were strong reinforced trades from the south-east, and we could see an incredible electrical storm behind us which we can only assume was the convergence. It never overtook us, but certainly hit the boats 150 miles astern as we were to learn on the radio the next morning. In the second case, the convergence was probably drawing the `pleasant' 12 knot north-easterly into it and they were unlucky enough to run into a VERY active part of the convergence, indicated by the violent shift to the south-west. After the incident west of Bora Bora we started making sure we had a pretty good idea where the South Pacific Convergence Zone was located, as this seemed to be the only place where really violent conditions might be encountered.

There are many times in the Pacific when you do not have nice clean sea room. The Tuamotus are a prime example, with many low atolls often accompanied by swift and irregular currents between them. Everyone who cruises out here is aware of how many boats end up on reefs. Satellite navigation may not have improved the situation, as many people rely on its accuracy and reliability and take chances that one would never consider when relying solely on celestial navigation.

Where to get weather information? The following are the sources which we used. We do not receive weather charts constantly with our weatherfax or listening to every spoken forecast, but when we are planning or making a passage, or when in an anchorage which would become exposed in the event of a wind shift, we try to keep very much on top of the weather. We also, of course, watch the sky and WIND DIRECTION which usually `tells the tail' if you listen!

As anywhere else, it is necessary to separate adiabatic (land and sea breezes) and local phenomenon effects which generally occur near the high islands from the general shifting of wind due to the approach of a frontal system. The steady direction of the South Pacific Trades is south-east. When the wind shifts to the east and north-east, particularly with diminishing velocity, then you had better be looking for a frontal system moving towards you from the south-west or west. When the velocity decreases at it moves north or north-west, the chances are pretty good that the frontal passage is going to be pretty fresh when the wind shifts to the south-west. When the wind is blowing out of the northern quarter, you want to be thinking ahead about shelter from the south-west and south.

Weatherfax

Many boats are now equipped to receive weatherfax charts. The following are the stations we have used in the Pacific, running from east to west. All frequencies are Upper Side Band, though the frequency actually used depends on the time of day and the distance from the station. All times given are UTC, and all schedules are daily.

NMC San Francisco : 4346, 8682, 12730, 17151.2 and 22527 kHz - transmits a schedule at 2019. We tried to get maps from this station with irregular success (due to poor signal strength). Their tropical analysis covering 30°N to 20°S and east of 160°W showed the ITCZ, which helped in getting out of the Gulf of Panama.

KVM 70 Honolulu, Hawaii : 9982.5, 11090, 13627.5, 16135 and 23331.5 kHz - transmits a schedule at 1147 and 2347. The charts we found most useful were their Tropical Surface Analysis transmitted at 0041, 0641, 1241 and 1841, which cover from 30°N to 50°S and from 110°W to 120°E. They proved to give the most useful information from Panama to the Galapagos and west to the Marquesas (140°W). However they do not show cold fronts, so we used ZKLF (see below) when we could get it reliably. (KVM 70 never seems to start automatically - we have always had to start their maps manually. ZKLF and AXM always start automatically).

ZKLF Wellington, New Zealand : 5807, 9459, 12550 and 16340.1 kHz - transmits a schedule at 0445 and 1645. At 0330 and 1530 they transmit a Surface Analysis for the South West Pacific (5°S to 60°S, 130°W to 170°E) which we used from about 130°W and found extremely useful. It often, but /not always, shows the South Pacific Convergence Zone. The symbol for the convergence should be a line of long dashes, though sometimes it appeared to me that they showed the convergence as a northern extension of a front rather than the dashed line of the convergence. It was then that clarification from Arnold or Tony's Net (see below) was very helpful.

ZKLF also transmits a Surface Analysis of the Tasman Sea at 0300, 0945, 1500 and 2145. This is very useful when sailing between New Caledonia, Fiji, Australia and New Zealand.

AXM, Melbourne, Australia : 5100, 11030, 13920 and 19690 kHz - prints a schedule at 0115. We found the Surface Analysis transmitted at 0210, 0815, 1430 and 2015, which covers from 10°S to 50°S and from 90°E to 165°E (Eastern Indian Ocean to New Caledonia), gives a good picture of what is moving across the Australian continent and into the Coral and Tasman Seas.

Spoken Weather Reports in Plain English

To supplement the weatherfax charts we like to get someone else's opinion and analysis of what is going on. Boats which do not have weatherfax often rely on one or more of the following - all that is needed is a good short wave receiver or transceiver.

Arnold's Net (ZK1DB) : 1431 kHz (20 metre Ham band) at 0400 - from Rarotonga, Southern Cook Islands, gives South Pacific weather information. He repeats, at easily copied speed, the weather situation as reported from Nandi, Fiji, which plots the position of the South Pacific Convergence Zone. He then repeats the weather from Papeeti, Tahiti, and finally from New Zealand. In each case there is an area forecast for the different island sub-groups. If you are a Ham operator you can talk to Arnold afterwards to clarify any points of particular interest.

Tony's Net (ZI1ATE) : 14315 kHz (20 metre Ham band) at 2100 - from New Zealand. There are always plenty of relay stations available. Don (VK4NN) who is probably more easily heard than any other station is usually on from 2040 onwards. Hams can call in and give their positions and request weather information. At about 2130 or so John (VK9JA) from Norfolk Island (Tasman Sea), or Harry (KL7NZ) from the American yacht Whalesong will come up, take the positions of those boats wanting weather, and then go off to another clear frequency (often 14302.5 kHz) and give a synopsis of weather for the South West Pacific including the South Pacific Convergency Zone, plus forecasts for the various positions where boats are located, as well as island groups. While it is nice to be a Ham and to talk to these folks it is not essential - often a boat that may be in the same general area will be getting information which is equally applicable to you.

Keri Keri Radio - John and Maureen Cullen in Keri Keri, on New Zealand's Bay of Islands, provide an excellent service for which you pay a very reasonable fee of $75 NZ per year ($40 US), advance payment not needed. They use the Marine SSB frequencies, so no Ham license is necessary. When on passage westwards from Tonga to Australia and south to New Zealand it is best to listen to Keri Keri on 4417 kHz from 0700 to 0730, or 4445 kHz from 0730 to 0830. After a day or so of listening you will understand their system and can give them a call, and they will put you on their roll call. They will then call your boat name, take weather information from you (set format), and give you a forecast for the next 24 hours at your location.

A great many of the boats going to or from New Zealand use Keri Keri Radio, and John's forecasts have proved to be very good. He will also relay messages to you which have been received by phone, fax, letter or radio and will make replies as per your instructions.

Pacific Maritime Mobile Net : 14313 kHz (20 metre Ham band) at 0400 - run by Fred (KH6UY) from Honolulu, Hawaii. (Sometimes uses 14300 if 14313 is busy). The warm-up session is from 0400 to 0430, followed by the roll call at 0430 for boats on passages all over the Pacific, each of which give a position and weather report. By participating, you are adding one more bit of weather information. Non-hams can get a good idea of the weather simply by listening.

There are many other sources of weather information such as local forecasts given on commercial or state stations in the various island groups. We have only used these in Fiji, which seems to have a good weather service and broadcasts in English. Tahiti may be good, but you have to understand French. Arnold give you the Tahiti forecasts on 14318 kHz in English at 0400.

We have found the sources listed to be reliable as to time of transmission and accuracy. Unlike the Caribbean, where NMN (Virginia) repeatedly tells you there are `no significant features' for the Eastern Caribbean, that is simply not the case in the South West Pacific. There are plenty of active features, and it is nice to be aware of them.

(2444 words)