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BLOG : INCREASED RISK OF TROPICAL CYCLONES THIS SUMMER

6/08/2007 12:00pm

Floods in the North, droughts in the South: La Nina

Last spring it was El Nino…this spring it’s La Nina, that’s the consensus from Jim Salinger at NIWA, along with Australian and American climate scientists. He says the probability of La Nina developing in the next two or three months is about 55%, which means by November we’ll have an active La Nina weather pattern. Granted 55% doesn’t sound like much, but when you compare it with the 10% probability of El Nino forming again, you realise they’re pretty good odds.

So what does La Nina mean for you?

Well that simply depends on where you’re living. Places like Northland, Auckland, Coromandel, Bay of Plenty and Gisborne/Hawke’s Bay can all expected more rain. That doesn’t mean your camping holiday is going to be rained out… it just means bigger rain events are likely with hopefully long sunny breaks in between. If you live on the South Island’s west coast, of if you live in Central Otago or Southern Canterbury, it could mean a drier than normal summer. But there are two things that all of New Zealand will have in common – more north easterly winds and slightly warmer temperatures.

The Threat to NZ

Keep in mind though that this La Nina event will be weak…so we’ll only experience a lmild version of La Nina conditions. But while a stronger La Nina back in 2000/2001 spawned no tropical cyclones that hit New Zealand, the risk is still high this summer. More lows will develop in the Coral Sea, between north east Australia and New Caledonia. This is the breeding grounds for our biggest storms and while we were lucky to be missed last time, that doesn’t mean this year we’ll be even safer. Certainly the risk is significantly higher than last summer.

The last direct hit was Cyclone Drena over 10 years ago in January 2007. I roughly looked back over the past 30 years or so and noticed NZ gets a direct hit cyclone about every 7 or 8 years…so in some sense we’re overdue…not that Mother Nature knows that. Jim Salinger agreed that it’s been quiet over the past decade but that you never know when one will strike.

Predicting Tropical Cyclones

Personally I ignore predictions of cyclone numbers. They predict numbers in America (and NZ), for eg in America “10 or 13 Hurricanes this season”. But they’re constantly getting it wrong! Last year, following the hurricane season that formed Katrina, forecasters were quick to point out that 2006 would be not quite as severe but still a major season. Only one dismal storm made landfall and only a handful formed out at sea. This year, another doom and gloom prediction for America…so far nothing has happened and many forecasters have changed their outlooks. That’s like saying in January “the All Blacks will win every game this year”… then as they start losing some, saying that “now they might not win all of their games this year”. Our weather partner in the USA weather.com doesn’t do cyclone predictions simply for that reason, it’s anyone guess. But you can predict if the conditions are weak or strong for growing big storms…and this year, while weak-ish, they’re still significantly higher than last year.

There is an increased threat of a tropical cyclone hitting New Zealand this Summer and an increased threat of more storms like the ones that have hit Northland. They will definitely form out to sea…the question is, will they make it to New Zealand…well unfortunately the best forecasters in the world can’t predict that this far out…so only time will tell.

WEATHER NEWS HEADLINES:

– Slightly cooler temperatures today and tonight across New Zealand thanks to the south westers.

– Could be a change to easterlies over the North next week… indicating a possible low in the northern Tasman

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