Higher risk of tropical cyclones this summer

File photo / NZ Herald

New Zealand and some of its neighbours have been put on alert for a higher than usual chance of tropical cyclones striking this summer.

Peak tropical cyclone season is usually from January to March.

Forecasting agencies in the South Pacific said for the coming tropical cyclone season, the risk for New Zealand was slightly higher than normal.

Niue, Samoa, the southern Cook Islands, Tokelau and Tuvalu also had an elevated cyclone risk.

However, cyclone activity for Vanuatu and New Caledonia was expected to be below normal.

The National Institute of Water and Atmospheric Research (Niwa) teamed up with the MetService and forecasters including the Australian Bureau of Meteorology and Pacific Island National Meteorological Services to compile the seasonal outlook.

"If an ex-tropical cyclone comes close to the country, the current background climate conditions suggest it has a higher probability of passing east rather than west of Auckland City," the forecasters said.

Eight to 12 tropical cyclones were expected for the 2014-15 season for the Southwest Pacific basin.

On average, New Zealand experienced at least one ex-tropical cyclone passing within 550km of the country every year.

Dr Andrew Lorrey, Niwa climate scientist, said February and March had historically been the months ex-tropical cyclones were most likely to hit New Zealand.

Dr Lorrey said people in countries with elevated risk warnings need not panic, but should stay vigilant.

"The first thing everyone should do is pay attention to their local meteorological service and national disaster management announcements," he said.

Southwest Pacific cyclones fell into five classes, with Category 5 deemed the most dangerous.

For the coming cyclone season, at least four storms were predicted to reach at least Category 3, with mean wind speeds of at least 118 km/h.

Another three may reach at least Category 4 strength, with mean wind speeds of at least 159km/h.

Forecasters said a Category 5 cyclone, with winds faster than 196km/h, was unlikely but could not be ruled out.

The most deadly cyclone in New Zealand's recorded history was Giselle, which in April 1968 caused the Wahine ship to sink with loss of 51 lives. Another three people died in other Giselle-related accidents.

An updated forecast would probably not be issued until the end of January.

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CYCLONE SEASON

* Cyclones in our region usually started at latitudes 10 to 15 South, with a "hive" in the Coral Sea and north of Vanuatu, said Dr Andrew Lorrey, Niwa climate scientist.

* These "hives" include an area of low pressure associated with a rain band called the South Pacific Convergence Zone.

* Tropical cyclones formed when cold air and warm air met. Cold air pushes warm air up. The new storm starts pulling in humid air from warm ocean water, and the winds swirl round and round, drawing in still more air.

* Tropical cyclones, typhoons and hurricanes always moved poleward -- in our case, to the south.