It has been a warm, wet winter in the United States. In fact, there has never been one warmer and wetter and that is official.

The National Oceanic and Atmospheric Administration, based in Washington DC, says the average temperature nationally in January and February was 3C. Normally, it is 0C.

But though this may be bad news for the overcoat trade and good news for raincoat makers, does it matter to the rest of us? Indeed it does. Washington is not the only place suffering unusual weather conditions, and El Nino, the phenomenon responsible, may provide canny investors with the chance to make a killing in certain key commodities.

The whole world knows about El Nino by now. In broad terms, what happens is that the trade winds which normally blow from east to west across the Pacific drop away. No one knows why. Colder water, which usually comes up from the ocean depths, stays down, enabling a huge mass of unusually warm surface water to take its place. This has a major effect on global rainfall, winds and weather generally, especially around the Pacific Rim.

The present El Nino dates to May last year when meteorologists detected a sudden extreme warming of the eastern Pacific. They concluded that not only was an El Nino beginning but that it would probably at least equal that of 1982-83, which was responsible for causing $13 billion (£9.4 billion) worth of damage the phenomenon's worst ever.

The most obvious impact has been on Indonesia, which has endured one of its worst droughts. The country is the world's biggest producer of robusta coffee but may produce 40 per cent less in 1997-98; production has also been hit in Colombia, Kenya, Uganda and Venezuela, contributing to a 5.5 per cent drop in exports in the 12 months to February from members of the International Coffee Organisation. Investment funds have moved swiftly into coffee futures; the May contract reached a peak of $1,912 a tonne during trading last week, its highest since last June.

But it is in energy that investors could benefit most. North America is the world's biggest consumer of energy; about 60 per cent of global demand for heating oil alone comes from the north-east of the US.

When the US has a warm winter, this demand drops sharply and the winter just ending has broken all records in that direction. At the same time, the price of crude oil has declined by about 40 per cent since September 1997.

Overall, world demand for oil has fallen by about 500,000 barrels a day as a direct result of this year's El Nino, according to Mr Fergus MacLeod, oil analyst with NatWest Markets. And Mr Michael Wilson, a US-based geologist who specialises in tracing the correlation between El Nino appearances, energy prices and company share performance, notes: "Domestic demand for heating oil and gas has dropped by 10 to 15 per cent."

As the price of oil has plummetted, so also has the relative performance of the major integrated oil stocks in the FTSE 100 index. Shell and BP have under-performed Footsie by about 20 per cent in the past six months.

The Organisation of Petroleum Exporting Countries (OPEC) hoped to stem the slide in the oil price with an agreement at the end of March to cut oil production by a 1.25 million barrels a day. But so far it has not worked; traders are uncertain about the level of stocks and doubtful about how quickly the promised cuts may reduce the surplus. no the La Nina effect. Put simply, the more rapidly an El Nino fades away the more vigorously "normal" weather conditions re-assert themselves.

"It is, almost literally, like the sloshing of water backwards and forwards in a bath," says Dr Mike Davey, a climate prediction scientist with the Meteorological Office in the UK.

"The eastern Pacific Ocean can rapidly become much colder and that basically reverses the El Nino. There's a high probability of us now going into a La Nina, which could mean that next winter in the US could be colder than normal."

So, even with OPEC and Asian economic problems, a colder than average winter in the northern hemisphere could see oil prices strengthen considerably. "You have to decide if the present price is the result of a confluence of factors which are temporary or if it represents a fundamental change in the situation. My judgment is the former," says Mr MacLeod. Citing spells of oil price weakness in the past 12 years, when oil stocks under-performed the market by 10 to 18 per cent, Mr MacLeod says they "marked time for a period of between two and 10 months until prices turned decisively, but then outperformed by 14 to 32 per cent during the recovery phase". He feels that the time to buy oil shares is "when pessimism in the market is at a maximum".

If we are indeed moving towards the end of El Nino, he might just be right.