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La Nina may pose increased Pacific cyclone threat

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?!

– Philip Duncan


Ken Ring on 21/08/2010 9:10am

The public do not know that La Niña is the normal situation. Easterlies spread cooler winds west along the equator, warm up and spread north beside Japan and come down from Alaska to California as cooler NWs. On the US east coast warm currents cause surface winds to spread north from the Caribbean then east across the Atlantic and then NE as the Gulf Stream.

La Ni√±a is not really a ‘condition’, anymore than the rotation of the earth is a condition. All good things come to point of change eventually and the normal flow is unsustainable because of the build-up of sealevels, just like the pushing of water one way in a bath. About every 3 years when the sea-level difference reaches 62cms, the water flows the other way as something called the El Nino. It only does so after the previous pattern reaches a peak. That peak is really the ‘La Ni√±a episode’. Then El Nino, being a restoration back to balance, is much shorter, usually about 1.5 years. Imagine the time taken for a hand pushing the bathwater, vs allowing the water to fall back. At the moment we have El Nino finishing, as normal rain patterns return. La Ni√±a may become evident after next January, but no one has a mandate to name it so before.

To say ‘La Ni√±a is forming’ is as misleading as saying normality is forming, because normality is not something that forms – just the opposite – patterns depart from the normal. Currently meteorologists are claiming that everything is now anomalous, and there is no norm, only a succession of imaginary mysterious departures, which is why they talk of climate change. In logic, you cannot have both the notion of climate change and the notion of average, because a changing baseline is no longer a baseline.

The cyclone/hurricane season usually gets going just after El Nino ceases and well before any peaking of La Niña. That is why the hurricane season is only in early stages later this year but, as I have said before on this forum, will be much more fully applying in 2011/2012. I believe the moon is as usual the culprit, the combination of perigee and lunar equinox, because cyclones all form within 6deg of the equator and with the same lunar conditions present. There will be a tropical low in December, 4 in January, 3 in February, 7 events in March and 3 in April. Some of these will be cyclonic. The danger will be mostly over by May of 2012.

I am aware that my methods are different to those Phil uses, so I will always come up with different results. Because I use the moon my opinions are based on a cyclicity allied to tides. My longrange observations are not intended as any criticism of Phil or Ww, but as augmention of their work in extended range (which I think is superior to most). However I am worried about impending drought that I have calculated for next year and seek the ear of any forum that will allow my viewpoint, in the hope it will help those most affected. So I thank Ww for this opportunity.

Overall, 2011 should be an average to drier year in all regions except Southland, with some seriously dry conditions developing in Northland, Waikato and Bay of Plenty. These districts, for the overall year, are expected to be drier by around 20-40%, with Northland and Bay of Plenty the most affected. The remainder of the NI will also experience lower rainfall than average overall, but to a lesser degree. Careful water management now may be something for agriculturalists to consider.

karamu49 on 21/08/2010 11:04pm

Very well put Ken, I too subscribe to the notion that Weatherwatch is indeed far superior to most other forecasting. I also subscribe to Ken Rings view and keep an open mind as to the opinions and views expressed, taking these into account I then form my own views based on them and prepare accordingly. Well done to both Phil and Ken.
Of interest Ww is the only weather forecasting service inviting viewers participation during a weather event thereby allowing us to see what is happening in different centres at that time, which in my opinion is excellent.

WW Forecast Team on 22/08/2010 2:06am

Thanks very much for the feedback Karamu49 – and for your thoughts on the weather ahead Ken.

Much appreciated.

Regards – WeatherWatch weekend team

Gary on 24/08/2010 12:54am

There will definitely be a tropical low on December 4, January 3, February 7 March and April and every day in between. Cyclones form on the Inter tropical convergence zone MORE THAN 5 degrees from the equator and where the sea surface temperature is above 26.5C. They form away from the equator where the coriolis effect is strong enough to start a rotation. Currently the convergence zone is north of the equator as can be seen here There are ALWAYS tropical lows along that line, some will form into cyclones. Since coriolis is a force due to the rotation of the earth, and sea temperature is a result of the sun, the moon plays no part and there is no correlation between moon phases and cyclone formation.
Saying there will be tropical lows on particular dates is like saying there will be gales in the southern ocean on particular days. Tell me which days there won’t be any, you’ll be struggling to find one.

Gary on 24/08/2010 6:27am

Sorry my mistake, they’re not actual dates Ken was forecasting, it’s was the numbers of tropical lows. It’s still just as ridiculous, there will be a hell of a lot more tropical lows than that. Unless he means tropical lows affecting NZ, but then last time I checked, NZ wasn’t in the tropics. And the statement “Some of these will be cyclonic”, all lows are cyclonic, by definition.

Ken Ring on 24/08/2010 8:30am

I believe a cyclonic event will occur in the first week of December over Fiji, forming around new moon. It should bring extreme weather to NZ in the second week. I expect torrential rain, thunderstorms and hail. The Waikato may be particularly affected.

Gary on 25/08/2010 1:00am

Now that can be verified, the wishy washy statements you made before that can’t. So extreme weather, (torrential rain, thunderstorms and hail) in the 2nd week of December, centred around the Waikato, I’ll mark it in my calendar. Rain in Fiji during the wet season is a given.

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