Weather Wise

I have tried to keep track in this column with the effects of El Nino, but its true magnitude only came home to me with one line in the latest El Nino update issued by the World Meteorological Organization.

After: "El Nino continues to dominate ... severe storms in certain areas ... Kenya hard hit by flooding ... 1,500 people have died of Malaria ... ", comes the startling line: "Talara Peru received five times its normal annual rainfall in a single day."

But when the Earth's climate has received such a big jolt, what happens next?

There are three possibilities: El Nino will drag on even longer than expected (which is unlikely because there are already strong signs of its fading); it will go away and everything will return to normal; or it will be followed by its sister, La Nina, which will play a totally different game of havoc with next winter's weather.

What happened with El (I feel we've known him long enough to be on first name terms) was that warm waters in the tropical Pacific heated the air, producing currents powerful enough to change the direction of the jet stream.

When La Nina occurs, she produces an opposite, but potentially no less drastic, effect. Waters near the equator become cooler than usual from the mid to east Pacific, while the western Pacific temperatures rise. This is accompanied by high pressure in the west and low pressure in the east, resulting in storms that blow up into North America.

Roughly speaking, the areas of the United States that have been having warm weather and even droughts this winter can expect a good deal of rain if it is followed by La Nina, while this year's rain-soaked locations will be dry.

At a Workshop on Seasonal Climate in Singapore last month, experts agreed that a return to normal was the most likely of the Post-Nino scenarios, but rated it as only a 50 per cent chance. The next most likely was La Nina at 35 per cent, with a prolonged El Nino trailing at 15 per cent. The fact that they are express such predictions of vastly different weather conditions in terms of percentage expectancies shows how difficult long- term prediction really is.

It's an ill El that blows no one any good.