19 NOVEMBER 1998
LA NIÑA - MORE CYCLONES FROM THE TROPICS
The chances of a remnant tropical cyclone crossing northern New Zealand
is raised this summer and autumn, according to research by NIWA climate scientists. And
there is a very real chance that some part of New Zealand will see either the high winds
or heavy rainfall these systems produce.
"During La Niña episodes the risk of a cyclone coming south and
reaching New Zealand from the tropics increases," said senior NIWA climate scientist
Dr Jim Salinger. "On average, Northland experiences two direct hits per decade, or
one chance in five in any given cyclone season.
"In La Niña years the risk increases to one chance in two for
Northland. In past La Niña years, at least one cyclone seems to have affect some part of
New Zealand. So it is fair to expect some area of New Zealand to receive their severe
weather effects during the period between January and April," he said.
"On average, about 11 tropical cyclones form in the South West
Pacific in any one season, which runs from November to April. Of these, only one is likely
to have major hurricane intensity winds of 166 km/h or more," said Dr Salinger.
"Once these cyclones leave the tropics and head south they may change into a strong
mid-latitude storm, often with high winds and heavy rain. It is almost impossible that a
cyclone of Hurricane Mitch intensity would affect New Zealand.
"During La Niña events, the atmospheric and oceanic conditions
are more favourable for the birth of tropical cyclones in the Coral Sea. Tropical cyclones
get their energy from the warm tropical ocean. This increases the chance of finding
tropical cyclones in our neighbourhood this summer.
"This summer a strong La Niña event is expected to affect New
Zealand. In the weak La Niña summer of 1996/97 Cyclone Fergus brought over 300 mm of rain
in the far north and 242 mm at Whitianga. During Cyclone Drena wind gusts as high as 124
km/h occurred at Mokohinau Island in the Hauraki Gulf," he added.
During previous La Niña seasons, 4 cyclones affected New Zealand in
1996/97, 2 in 1988/89, 2 in 1975/76, 2 in 1973/74 and 1 in 1970/71.
Last month NIWA announced that because of the La Niña event, more
tropical cyclones would occur in Melanesia this year, but fewer would occur in Polynesia.
For further information:
Tel: 09 375 2053
after hours 09 527 3939