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| The general idea, when planning the passage between Tonga and New
Zealand, is to choose a weather window that has the most potential for favourable winds
for the longest period of time. This is very difficult to do and requires a great deal of
guesswork and luck. The distance between Tonga and NZ is approximately 1100 miles, however
sailboats almost never sail in a straight line and additional miles are inevitable. For
planning purposes we assume 120 mile days (@ 5 knots) average. Therefore this passage was
expected to be 9 days long. |
| The best weather forecasts can do is project 5 days. This is where
the guesswork and luck come in handy. What will happen after the first five days?
The weather tends to be more active the closer one approaches NZ as there is an almost
constant parade of Lows and fronts passing over the island nation. It generally is a
matter of luck to arrive off the coast and have favourable winds. |
| Typically a weather window for this passage happens when a Low
passes south of Tonga and is followed by a High in the Tasman Sea and/or south of
Australia. This is what we were waiting for and what we finally saw on NZ weather faxes and the U.S. Navy model on
the Internet. The passing of the Low means the winds will swing to the southeast, followed
by the High which will further swing the winds to the east. As the high moves north and
east, the winds should continue moving counterclockwise through northeast, north,
northwest, and finally west. The speed at which the High moves will affect how long these
favourable winds remain. If the High moves quickly and is followed by another Low then the
winds will become an unfavourable southwest and south. If the isobars are compressed
('squashed') by additional following Highs, winds may become very strong, building high
seas and generally making a passage miserable to say the least. |
| In addition to this general movement of Highs and Lows in this
part of the Pacific, small but intense Lows can develop unexpectedly within the High area
that one is sailing through. This situation can become very hazardous. Three of our
friends left Tonga in the middle of October and got caught in one of these Lows. They were
forced to heave to for 3 days waiting for the winds and seas to calm down. Their passage
took over two weeks to complete. |
| We were very lucky. We left Tonga at the end of a passing Low with
a nice high sitting in the Tasman Sea extending south to a second high below Australia. As
long as this double High remained stable, no sneaky Lows appeared, and other Lows and
fronts passing over NZ did not intensify, we had a good chance of a reasonable passage. |
| As it turned out, the High lingered, almost stalled, changed
shape, but remained in the area for twelve days causing very light winds through the
entire area. The Lows and fronts marching across NZ were pushed further to the east and
the strong winds never materialized. We motored a lot, especially through the last third
of the passage, never saw winds above 18 knots or seas above 2 metres. It took us ten
sailing days to do the passage and we sailed 1200 miles at an average speed of 5.1 knots.
We sailed on a port tack for nine days, changing to a starboard tack for the last day
only! The last twelve hours we motored against a south wind of less than 10 knots which
was the only truly unfavourable wind the entire time. |