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Isaac Lashes Haiti, Heads for Florida Keys and Gulf Coast

Tropical Storm Isaac could strengthen into a hurricane as it approaches the U.S. Gulf Coast, and the movement of two weather systems over the U.S. mainland will determine where the storm goes ashore next week.

The movement of the low pressure systems could cause Isaac to move a little more westward, said Keith Blackwell, meteorologist at the University of South Alabama’s Coastal Weather Research Center in Mobile.

“This could keep it heading more northwest and not really recurving, and increasing the risk that it will hit a little farther west — Alabama, Mississippi, or southeastern Louisiana,” Blackwell said. “New Orleans will really have to watch this.”

As of 5 p.m., the center of the storm was just off the northern coast of eastern Cuba. It was moving northwestward at abouut 20 mph (32 kph), and its strongest winds were blowing at about 55 mph (88 kph).

The storm lashed Haiti and eastern Cuba with high winds and heavy rain earlier today and will move into the Straits of Florida — which separate Cuba, the Bahamas and the Florida Keys — by early Sunday morning. The storm is expected to intensify in the Straits and could become a minimal hurricane with winds exceeding 74 mph (119 kph) as it approaches the Keys late Sunday night.

Once past the Keys, Isaac will encounter conditions favorable for strengthening as it makes its trek to the Gulf Coast. Hurricanes draw their strength from ocean water that has been heated to at least 80 degrees Fahrenheit (27 degrees Celsius), and in most areas of the Gulf, the water temperature is about 86 degrees Fahrenheit (30 degrees Celsius). And upper level winds that could disrupt the storm’s momentum and cause it to weaken will be minimal, which also could allow it to strengthen.

“The possibility of this thing becoming a major hurricane (with winds exceeding 110 mph, or 177 kph ) is going up,” Blackwell said.

Residents of the Keys — a low-lying string of islands stretching about 150 miles (241 kilometers) from the southern tip of the Florida Peninsula into the Gulf of Mexico — were getting ready for Isaac Saturday as many tourists left the islands.

Jeff Pinkus, a resident and former mayor of Marathon, the second-largest city in the Keys, said a “steady stream of traffic” was moving northward on U.S. 1, the only highway from the islands to the mainland. Shelters also have opened for residents who want to ride out the storm in a secure building, Pinkus said.

Despite the departure of visitors, the economic impact of Isaac may not be as severe as it might have been because emergency management officials did not order a mandatory evacuation of tourists, Pinkus said.

“It takes hours for the tourists to leave and months for them to come back, so I’m sure all the businesses, restaurants and hotels are thrilled that a mandatory evacuation was not called,” Pinkus said. “I’m sure there will be a party atmosphere tonight on Duval Street in Key West.”

Meanwhile in Tampa, NBC News reported Saturday that Republican National Committee Chairman Reince Priebus  announced that the Republican National Convention, scheduled to begin Monday, will be postponed until the danger from Isaac is past. The storm is expected to be in the Gulf of Mexico offshore from Tampa Monday afternoon.

Although the center of the storm is not expected to cross Tampa, it could be close enough to cause some problems there, said Jeff Houck, who writes for the Tampa Tribune. As Isaac passes, it could push a mound of water into Tampa Bay, which Houck described as “a three-sided bathtub.” If the storm moves slowly and happens to arrive at high tide, there could be some flooding around the arena where the convention is being held, Houck said.

“It’s going to be wet, definitely wet,” Houck said.

Willie Drye has been writing about hurricanes and other topics for National Geographic News since 2003. Read more about Tropical Storm Isaac on his blog, Drye Goods.