Heat is the engine that drives a hurricane, the fuel that forms it over the Sahara Desert this time of year and the force that makes it grow as it moves across the warm, late-summer waters of the Atlantic Ocean and the Caribbean Sea into the even warmer waters of the Gulf of Mexico.

Hurricane Elena actually spawned near the mountains of Niger in the southern Sahara. She began as no more than a dusty swirl of hot, dry air that was carried into the upper atmosphere by the eddies that roll air around the mountains of Africa in a never-ending circle.

Only 10 percent of the low pressure swirls that begin in the Sahara make it to the Atlantic, only 10 percent of those become organized tropical depressions and only 10 percent of those become hurricanes.

Elena quickly joined the 10 percent of the 10 percent club and marched so fast out of Africa that weather forecasters at the National Hurricane Center in Coral Gables, Fla., said they had never seen a storm move across the Atlantic as fast.

"This thing came off Africa running like a deer. It's amazing," said the center's Hal Geerish. "The river of air that's steering it was moving at 35 miles per hour, which is faster than any storm we can remember."

Elena is one of at least 100 "tropical waves" that cross the Atlantic each hurricane season.

By the time it touched land in Puerto Rico, Elena had become a tropical storm. Land masses tend to dissipate circular storms like Elena but it marched across Puerto Rico, Haiti and Cuba without slowing, developing hurricane winds of 75 miles an hour while it was still tangled up in the mountains of southeastern Cuba.

Sucking up more heat energy from the Gulf Stream, Elena moved on Thursday into the Gulf of Mexico where the relatively shallow waters had reached a summer-high temperature of 87 degrees.

At the same time, Elena's steering winds had inexplicably slowed to 15 miles an hour. That sounds good but it is not. When a hurricane slows over a warm shallow body such as the Gulf, it can only gather strength.

Elena's 85-mph winds rose Thursday to 100 mph, and by 3 p.m. Friday, the fifth hurricane of the season was still sitting over the Gulf 130 miles west of Florida panhandle city Pensacola.

"The longer it stays over those warm waters, the worse it's going to get," the Hurricane Center's James Lynch said yesterday.

"This storm is right at the threshold of becoming a major hurricane."

It is difficult to predict the direction of a hurricane, especially one moving as slowly as Elena.

Elena's birth in late August is near the peak of the average hurricane season, early September. Weather records show that two-thirds of the more than 470 hurricanes tracked since 1900 occurred in August and September.

Elena's path out of the Caribbean, across Cuba and then northwest toward the upper Gulf coast is along what Floridians call "Hurricane Alley."