High risk of tropical cyclones for NZ
South pacific faces 8 to 10 storms this season
By MICHAEL FIELD - Fairfax Media | Friday, 26 September 2008

Climatic conditions this summer give New Zealand an increased risk of being hit by a tropical cyclone, NIWA says in a forecast.

"There is just over a four out of five chance of an ex-tropical cyclone passing within 500 kilometres of the country sometime between November and May, with the highest risk districts being Northland and Gisborne," NIWA says.

"By the time such systems reach New Zealand they are no longer classified as tropical cyclones, but can still cause strong winds and heavy rainfall."

The most common months for ex-tropical cyclones to affect New Zealand are January to March.

New Zealand is at an increased risk because of the neutral El Nino/Southern Oscillation (ENSO) conditions.

Across the Pacific the coming tropical cyclone season, from November 2008 - May 2009, will see a normal risk of cyclones.

There is a reduced risk in parts of French Polynesia.

"There is a good chance that the first tropical cyclone of the coming season in the South Pacific region may occur before the end of December, which is normal during neutral seasons."

They expect on average eight to ten cyclones over the entire South Pacific region during a neutral ENSO season.

Peak cyclone occurrence is usually from January to March.

In seasons with similar climate backgrounds, several tropical cyclones usually occur in the region between Vanuatu, New Caledonia, Fiji, and Tonga, while a few affect other areas.

In an average season about half of the tropical cyclones that develop reach hurricane force with mean wind speeds of at least 64 knots (118 km/h).

From here.