With tropical storm warnings an almost weekly occurrence this summer, scientists are working hard to determine why this year?s hurricane season is likely to be twice as dangerous as normal.

Recently, scientists at the National Oceanic and Atmospheric Administration and hurricane forecaster Dr. William Gray both said there was a 95 to 100 percent chance of 2005 being an ?extremely active? hurricane season, with over twice the average number of storms.

Only two months into the season there have already been five tropical storms and two hurricanes.

In only 12 previous years since 1851 have two or more tropical storms formed in the month of June, according to NOAA?s data, while July saw ?unprecedented tropical cyclone activity in the Atlantic basin?.

NOAA said 18 to 21 tropical storms are expected by the end of the season in the middle of November, while the average is ten. Nine to 11 of these storms are expected to become hurricanes, which is well above the average of six hurricanes.

But NOAA said an even more dangerous statistic is that five to seven of these hurricanes are expected to form into major hurricanes, packing winds of over 100 miles per hour. The average number of major hurricanes per season is two to three.

Bermuda Biological Station for Research scientists Dr. Henry Diaz and Dr. Rick Murnane said four factors have combined to make this year?s hurricane season unusually intense.

Rising sea surface temperatures in the tropical North Atlantic, weak ?vertical sheers? of air coming off the East Coast, low atmospheric pressure at the sea surface and the absence of an ?El Nino? effect have all occurred this year.

?The sea surface is warmer than it has been in the last several decades,? Dr. Murnane said.

He called this phenomenon the ?Atlantic multi-decadal oscillation?.

?The heat in the surface of the ocean is the fuel that drives the storm,? he said. ?Storms can only form over very warm water.?

He said ocean temperatures of 82.4 degrees Fahrenheit are optimal for hurricane growth.

This oscillation is expected to persist for years, he said.

?Another reason is that we don?t have much vertical sheer in the atmosphere,? he added.

Vertical sheers are waves of air that burst into the Atlantic from the North American continent, he said.

Tropical Storm Harvey, which brushed by Bermuda last week, was prevented from becoming a hurricane because the vertical sheer increased, said Dr. Diaz.

?Harvey was never allowed to reach hurricane status,? said Dr. Diaz, who is on sabbatical from the NOAA at BBSR. ?If it was not for the vertical sheer, for sure it was going to be a hurricane. It was a storm that wanted to grow.?

Dr. Murnane said another reason behind the increase in hurricanes is a ?relatively low atmospheric pressure on the sea-surface?.

Areas of low pressure tend to be associated with cyclones as the air is moving upward as opposed to downward, he said.

And Dr. Diaz said there is no El Nino to alter sea-surface temperature in the eastern tropical Pacific.

?The El-Nino diminishes the number of storms,? he said.

For Bermuda, the increase in storm estimates means that the Island is more likely to be hit. But the scientists cautioned that it remains a small target for storms compared with the Caribbean islands or the long coastlines of Florida and the other US southern states, where the odds are higher that a storm will make landfall.

?Bermuda is a small spot and gets hit by random chance,? Dr. Diaz said. ?But if there are more hurricanes around we are more likely to be hit.?

Technology also plays a role, as storms that would not even have been noticed 100 years ago are in the news and on television 24 hours a day today.

?This year Tropical Storm Brett was in the Gulf of Mexico, but was only a tropical storm for 12 hours. A hundred years ago this would not even have been recorded.?

Academia is still debating whether or not global warming is having an affect on extreme weather patterns.

Prof. Kerry Emmanuel of M.I.T. leads the side which contends that global warming is a factor in increased hurricane strength and activity.

?My results suggest that future warming may lead to an upward trend in hurricanes? destructive potential, and taking into account an increasing coastal population, a substantial increase in hurricane-related losses in the 21st century,? Prof. Emmanuel said in Nature.

However, Dr. Gray, disagrees, saying there is no evidence to blame global warming.

Dr. Gray said hurricanes are only increasing in the Atlantic but not in other parts of the world.

He said if global warming were the cause of the increase, he would expect to see more typhoons in the Pacific.

As Dr. Murnane suggests, Dr. Gray said the heightened Atlantic major hurricane activity since 1995 is from an increase in thermohaline circulation (THC) in ocean currents, which increases water temperatures.

An increase in THC since 1995 has strengthened the Inter-Tropical Convergence Zone (ITCZ) where many hurricanes are formed.