The past four years have seen the most extreme hurricanes since records began, according to analysis by Professor William Gray, an atmospheric scientist based at Colorado State University. If the pattern is sustained, he argues, severe winds will continue to blow stronger and more frequently than ever - and the pattern is likely to be sustained for decades. This year there have been 10 hurricanes and three "intensive" hurricane systems, with winds at more than 110mph - almost twice as many in both categories as normal.
The hurricane "season" climaxed with Hurricane Mitch, the fourth most powerful storm ever seen in the Caribbean, which killed 10,000 people, devastating Nicaragua and Honduras. The US government described Mitch as "the worst disaster we have seen in this hemisphere".
Prof Gray's team - which also includes a senior US government meteorologist - predicts that next year there will be nine hurricanes and four intense ones. The latter are particularly important, says Prof Gray, because "they cause the majority of hurricane-spawned destruction". Although they make up only about one quarter of all major storms, they are responsible for 80 per cent of the damage and loss of life.
The scientists estimate that next year the Caribbean and the United States' Atlantic coast will be twice as likely - and the US Gulf coast one-and- a-half times as likely - to be hit by one of these intense hurricanes.
"Our concern is that because of the population build-up along the US east coast, property damage could be severe," adds Professor Gray.
Since 1995, the scientists say, there have been 33 hurricanes and 15 intense ones, making the period the "most active four consecutive years of hurricane activity on record". The effect is all the more dramatic because the 25-year period up to 1994 was unusually "quiescent".
The scientists base their predictions for next year on studies of a whole series of weather phenomena, ranging from the temperature of the Pacific Ocean to rainfall in the West African Sahel, which have proved to be good indicators of hurricanes in the past. The "La Nina" cold current in the Pacific goes with hurricanes in the Atlantic. It began to take hold last year and the scientists expect that it will persist through the next hurricane season. Wet years in the Sahel are also linked with Atlantic hurricanes: more rain fell than usual this year, and this too is expected to continue. Stratospheric winds, which change direction every few years, are expected to go on blowing from the west, which produces hurricanes. And global warming is also thought to make the storms worse as they draw extra energy from warmer seas.
The most important factor, scientists believe, is the North Atlantic Conveyor Belt Current, which carries warm water from the Caribbean to east of Greenland as the Gulf Stream, and takes a deep cold water current back again.
When it is strong, they say, there are plenty of hurricanes. They believe it strengthened between 1994 and 1995 and is now more forceful than for 30 years. The strength of the current may well continue, bringing more intense and frequent hurricanes "for two or more decades".Reuse content