FORECASTERS were predicting months ago that this would be a bad year for hurricanes, but the number of storms is unprecedented.

With three months of the hurricane season remaining, the risk of more devastating storms is extremely high. All the ingredients for a deadly series of hurricanes are in place. Sea temperatures are at their highest recorded levels in “Hurricane Alley”, the stretch of tropical seas that spawns hurricanes across the Atlantic, the Caribbean and the Gulf of Mexico.

Hurricanes feed off ocean waters of at least 26.5C (80F), and the warmer the water, the better for hurricanes. The waters also need to be about 50m (150ft) deep, because storms churn up seas so violently that they can drag up cold water, which kills the storm.

Hot, humid air wafting off a warm tropical ocean is the fuel that drives tropical storms and hurricanes. As the wet air rises, it cools and condenses into huge thunderclouds, at the same time unleashing a phenomenal amount of heat that powers the hurricane. An average hurricane has the energy of 10,000 nuclear warheads.

Another key ingredient is gentle winds miles above. If the winds are too strong, or hit the storm head on, they topple the clouds and decapitate the storm. This is called wind shear, and this summer the wind shear values are up to 40 per cent below normal.

The lack of any El Niño this year has helped. This climate phenomenon arises in the Pacific but sends high-level winds across the Atlantic and kills off hurricanes. Hurricanes are also susceptible to dust storms off the Sahara, but there have been few this year.

Compounding all this, the weather patterns are steering tropical storms straight for Florida. Normally a large area of high atmospheric pressure, the Bermuda-Azores High, sits over the Atlantic and allows the sea to bake under the tropical sunshine. The hurricanes spin around the edge of it.

This summer, the Bermuda High has reached far to the south and west, and is steering hurricanes towards Florida and the Gulf of Mexico, which explains the track of Hurricane Katrina. The same system has also been dragging warm tropical air northward into the Midwest, leading to a very hot and sticky summer.

Climate experts are debating whether global warming is also to blame, but the remark-able intensity of this season’s hurricanes can be blamed partially on global warming helping to heat the seas.

And the outlook for the next 15 years is grim. A cycle of hurricane activity goes round every 20 to 50 years. Since 1995, activity has been growing stronger and will probably continue to do so until about 2020 — and the threat of the most intense hurricanes, categories 3 to 5, is especially high.

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