Hurricane Kate roared across Cuba yesterday into the open waters of the Gulf of Mexico, taking aim at the Gulf Coast. It was the seventh tropical storm to reach hurricane strength this year but only the 16th to form in the last half of November since hurricane records were first kept in the late 1800s.

Hurricane experts said Kate formed so late in part because the cold northerly November winds that normally discourage tropical storms have not materialized this year and in part because the jet stream that blocks hurricane motions in the upper atmosphere has not moved south, as it usually does in November.

If Kate should make landfall in the United States this late in the year, it would also make history. Only three November hurricanes have touched land in the United States. And only one has touched down later than the Gulf-bound Kate. That was Nov. 30, 1925, when an unnamed hurricane struck Tampa, Fla.

"Normally, the waters in the Gulf of Mexico and the northern Caribbean get cooler by the middle of November, but this year they're slow to cool," Robert Sheets, deputy director of the National Hurricane Center in Coral Gables, Fla., said in a telephone interview.

"The formation and movement of this hurricane is unusual because the weather up north is unusual," he added.

Sheets said Kate's appearance makes her the seventh hurricane and the 11th tropical storm to be formalized with a name to form off the southeastern United States this year, a slightly higher than average number for hurricanes and tropical storms.

"We get an average of 1.5 to 2 hurricanes striking the continental U.S. each year," Sheets said. "What's unusual this year is that we've already had five, not counting Kate. We've had Bob, Danny, Elena, Gloria and Juan."

At 3 p.m. yesterday, the eye of the newest hurricane passed over Havana. The storm pounded Cuba with 100 mph winds, knocking out telephones, electricity, gas and television. About 300,000 people were evacuated throughout the island, Cuba's official news agency, Prensa Latina, reported. Wire services said the hurricane was felt from the northern tip to Cienfuegos on the south coast, with nine-foot waves crashing into the waterfront at Havana.

As the storm moved into the Gulf of Mexico, it whipped Key West with 105-mph gusts, knocking down power lines and submerging roadways. Last night, the storm, about 150 miles west-southwest of Key West, appeared headed west-northwest at 15 to 20 mph.

Concern will shift from the Keys to the Gulf Coast today, National Hurricane Center director Neil Frank said last night. "We expect a turn to the northwest . . . maybe toward the Alabama, Mississippi, northwest Florida coast," he said.

"This is not a superstorm, but people should take it seriously," Frank said. "People can get killed in a storm like this."

Hurricane warnings in effect for South Florida were lifted for all but the lower half of the Florida Keys.

Thousands of people left Key West, the southernmost of the keys, moving out along U.S. 1 along the 150-mile-long "Overseas Highway" to the mainland. Schools were closed as were most businesses, except for Key West bars promoting hurricane parties. At one, bartenders unveiled still another rum cocktail -- "Kiss Me Kate."

Forecasters said their efforts to track the hurricane were hampered by Cuba's refusal to allow U.S. weather-reconnaissance aircraft to enter Cuban airspace.