Weather Watch: La Nina may pose increased Pacific cyclone threat

Drena's huge seas pounded the Ports of Auckland container terminal in 1997. File Photo / NZ Herald

The Pacific Islands may be facing an increased threat of a Tropical Cyclone this coming cyclone season as scientists around the world confirm La Nina is in the early stages of forming.

La Nina is the opposite of El Nino, when warmer waters shift to our part of the world - and warm water is the main fuel for low pressure systems. During La Nina we see more lows forming north and north west of New Zealand.

I'm a firm believer that any lows that form in the northern Tasman Sea or the Coral Sea always pose serious threats to New Zealand, so the fact that we're heading into La Nina means those in the north may see a continuation of the big rain systems we've been seeing over the past few weeks.

It also increases the risk of tropical cyclones hitting our South Pacific island neighbours, such as Vanuatu, Fiji, Samoa and the Cook Island - but decreases the threat to Tahiti.

La Nina increases the chances of tropical storms forming on our side of the International Dateline and often puts New Zealand at a slightly increased risk of seeing a named storm come our way. It's certainly been a long time since we had a direct hit. My memory may be wrong but I believe it was the summer of 96/97 that saw Fergus, Drena and Gavin affect New Zealand.

NIWA and the other scientific organisations involved in predicting La Nina and El Nino events have up to 80% confidence that La Nina is forming right now (and certainly current weather patterns back this up) but they believe it will ease in early 2011.


The problem with discussing La Nina and El Nino is that it's not a weather forecast. It's a climate prediction. So while we expect more lows, perhaps bringing more rain to eastern parts of the North Island, it's pretty hard to say summer will be a wetter one, or your January holiday isn't going to be so good. One big high at the right time could see dry weather for several weeks in the slower moving summer months.

It's about overall statistics based on previous events. New Zealand, being the narrow mountainous nation that it is, sometimes completely bucks the trends. We were in La Nina a couple years ago that saw widespread droughts from Northland to Southland. It's clear to see why it's hard to forecast accurately long range for New Zealand when you see just how tiny we are and how large highs and lows are - often several times the size of our country.

Our location in the roaring 40s also throws a spanner in the works.

Sigh....who would be a forecaster here?!