KEY WEST, Fla. (AP) — Tropical Storm Isaac gained fresh muscle Sunday as it bore down on the Florida Keys and forecasters warned Isaac could grow into an extremely dangerous Category 2 hurricane as it begins tracking toward the northern Gulf Coast.
Isaac's drew new strength early Sunday during a warm-water crossing of the Florida Straits after causing weekend havoc in Cuba, where it downed trees and power lines, and after leaving four dead earlier in Haiti.
On Key West, locals followed time-worn storm preparedness rituals while awaiting the storm after Isaac swamped the Caribbean and shuffled plans for the Republican National Convention. Forecasters said the storm was expected to reach the archipelago later Sunday or Sunday night at or near hurricane strength.
"Currently Isaac is a tropical storm that's expected to become a hurricane as it reaches Key West ... then it will move into the Gulf of Mexico and is expected to strengthen" further, said Meteorologist Jessica Schauer with the U.S. National Hurricane Center in Miami.
"Our forecast is that as the system moves northward it is forecast to strengthen to a Category 2," she said, adding an ultimate landfall is possible on the northern Gulf Coast late Tuesday night or early Wednesday morning.
"Definitely the northern Gulf Coast should be preparing for a hurricane right now," she added, speaking with The Associated Press by telephone.
A Category 2 hurricane is capable of top sustained winds of 96-100 mph (154-177 kph). Schauer cautioned that Isaac also poses a threat of destructive storm surges though she noted forecasts extending out as far as Tuesday or Wednesday are subject to greater uncertainty.
Thus, she said, a wide swath of the Gulf Coast, including the thousands of people gathering for the Republican National Convention in Tampa set to begin Monday, should remain alert to the storm's progress.
Forecast models show Isaac likely won't hit Tampa head-on, but it could have lashed the city with rain and strong winds just as the convention was ramping up. A tropical storm warning was extended north of Tampa Bay.
Convention officials said they would convene the convention briefly on Monday, then immediately recess until Tuesday afternoon, when the storm should have passed. Florida Gov. Rick Scott, a Republican, declared a state of emergency and canceled his plans to attend convention events on Sunday and Monday.
As of 5 a.m. EDT, the storm was centered about 205 miles (330 kms) east-southeast of Key West, according to the U.S. National Hurricane Center in Miami. Isaac had strengthened in recent hours, with maximum sustained winds of 65 mph (100 kph) while crossing open water.
Forecaters said a hurricane hunter plane found the top sustained winds had increased from about 60 mph (95 kph) just hous earlier.
Isaac was then forecast to move over the southeast Gulf of Mexico on Monday. It was moving to the northwest toward the Keys at 18 mph (30 kph). Tropical storm-force winds extended outward up to 205 miles (335 kph) from the center, giving Isaac a broad sweep as it passed.
A hurricane warning was in effect for the Keys, including the Dry Tortugas and for the west coast of Florida from Bonita Beach south to Ocean Reef, among some other areas, authorities said.
Meanwhile authorities said a new hurricane watch has been issued from the mouth of the Mississippi River — not including the New Orleans metro area — eastward to Indian Pass., Fla.
From Key West, a steady line of cars moved north along the Overseas Highway, the only road linking the Florida Keys, while residents boarded up windows, laid down sandbags and shuttered businesses ahead of the approaching storm. Even Duval Street, Key West's storied main drag, was subdued for a weekend, though not enough to stop music from playing or drinks from being poured.
"We'll just catch every place that's open," said Ted Lamarche, a 48-year-old pizzeria owner visiting Key West to celebrate his anniversary with his wife, Deanna. They walked along on Duval Street, where a smattering of people still wandered even as many storefronts were boarded up and tourists sported ponchos and yellow slickers.
"Category None!" one man shouted in a show of optimism.
When it hits, winds will be "enough to knock you over," National Hurricane Center spokesman Dennis Feltgen said.
The Keys were bracing storm surge of up to four feet, strong winds and the possibility of tornadoes. The island chain's two airports closed Saturday night and volunteers and some residents began filing into shelters.
"This is a huge inconvenience," said Dale Shelton, a 57-year-old retiree in Key West who was staying in a shelter.
Isaac has already left a trail of suffering across the Caribbean.
The storm's center made landfall Saturday near the far-eastern tip of Cuba, downing trees and power lines. In the picturesque city of Baracoa, the storm surge flooded the seaside Malecon and a block inland, destroying two homes.
At least four people were reported dead in Haiti, including a 10-year-old girl who had a wall fall on her, according to the country's Civil Protection Office. The government also reported "considerable damage" to agriculture and homes. Nearly 8,000 people were evacuated from their houses or quake shelters and more than 4,000 were taken to temporary shelters.
The Grise River in Haiti overflowed north of Port-au-Prince, sending chocolate-brown water spilling through the sprawling shantytown of Cite Soleil, where many people grabbed what possessions they could and carried them on their heads, wading through waist-deep water.
Scores of tents in quake settlements collapsed. In a roadside lot in Cite Soleil, the dozens of tents and shelters provided by international groups after the earthquake were tossed to the ground like pieces of crumpled paper, and the occupants tried to save their belongings.
Associated Press writers contributing to this report were: Bill Barrow in Tampa; Trenton Daniel and Evens Sanon in Port-au-Prince, Haiti; Peter Orsi and Anne-Marie Garcia in Havana; Fernando Gonzalez in Baracoa, Cuba; and Ezequiel Abiu Lopez in Santo Domingo, Dominican Republic.