Updated at 7:40 a.m. ET: Tropical Storm Isaac dumped heavy rains on Haiti on Saturday, threatening floods and mudslides in a country where hundreds of thousands of people remain homeless more than two years after a devastating earthquake.

Lashing rains and high winds were reported along parts of Haiti's southern coast and in the Haitian capital of Port-au-Prince, where more than 350,000 survivors of the 2010 earthquake are still living in fragile tent and tarpaulin camps.

Intermittent power outages affected the greater Port-au-Prince area in the early hours of Saturday as Isaac bore down on the impoverished Caribbean country.

At 5 a.m. ET, the U.S. National Hurricane Center issued a hurricane warning for the Florida Keys, including the Dry Tortugas, the west coast of Florida from Bonita Beach southward and Florida Bay.

It also issued a hurricane watch notice for Florida’s east coast from Golden Beach southward.

The NHC also said the Bahamas government had issued a hurricane watch for Andros Island.

The NHC's notice at 5 a.m. said Isaac had maximum sustained winds of 60 mph, down from 70 mph earlier Saturday, and was about 150 miles southeast of Guantanamo, Cuba.

'Life-threatening flash floods'
The Weather Channel reported that bands of heavy rain triggered flooding in Puerto Rico through Friday, even with Isaac's center well to the southwest. A bridge collapse and mudslide was reported early Friday. Power outages were also reported. The U.S. Virgin Islands were also affected.

The Weather Channel said heavy rainbands on the cyclone's eastern flank were expected to continue to hammer Haiti and the Dominican Republic.  

Follow Isaac's path with our storm tracker

Storm total rainfall of 8 to 12 inches is possible, with up to 20 inches locally, The Weather Channel said. Additionally, 4- to 8-inches of rainfall, with isolated incidents of 12 inches, was possible in Jamaica.  

"Life-threatening flash floods and mudslides will likely result from that amount of rain," it warned.

Aid workers prep Haiti's tent city residents for Isaac's onlsaught

Isaac's march across the Caribbean comes as U.S. Republicans prepare to gather in Tampa, on Florida's central Gulf Coast, for Monday's start of their national convention ahead of the November presidential election.

The convention is still expected to proceed as planned but Gulf of Mexico operators began shutting down offshore oil and gas rigs on Friday ahead of the storm.

But the biggest immediate concern was heavily deforested Haiti.

On Friday, the government and aid groups evacuated thousands of tent camp dwellers but many Haitians chose to remain in their flimsy, makeshift homes, apparently out of fear they will be robbed, said Bradley Mellicker, head of disaster management for the International Organization for Migration (IOM).

"There's a lot of people who are resisting because they are scared of losing what little they have now," Mellicker said.

Churches, schools are shelters
About 3,000 volunteers from the government's Civil Protection office were dispatched across Haiti, warning people about flood and landslide risks, and about 1,250 shelters -- schools, churches or other community buildings -- that have opened their doors to house people seeking refuge from the storm.

But Red Cross officials said the number of shelters could be grossly inadequate and Prime Minister Laurent Lamothe acknowledged Haiti had "limited means" to ensure public safety.

Red Cross and IOM representatives joined government officials in trying to evacuate 8,000 of the "most vulnerable people," including 2,500 sick and disabled, from 18 tent camps in low-lying coastal areas of Port-au-Prince.

Live updates and analysis from weather.com
Transcript of weather.com experts answering Isaac questions 

Many Haitians, most of whom scrape by on less than $1 per day, consider disaster an inevitable part of life in the poorest country in the Americas.

"We live under tents. If there's too much rain and wind, water comes in. There's nothing we can do," said Nicholas Absolouis, an unemployed 34-year-old mechanic at one camp for homeless people on the northern edge of the chaotic capital.

"There are still too many people living in the camps. There's a good chance that those might be destroyed with the passage of the cyclone," said France Hurtubise of the International Federation of Red Cross and Red Crescent Societies in Haiti.

Flooding could also help reignite a cholera epidemic, which has killed more than 7,500 people in Haiti since the disease first appeared in October 2010, foreign aid workers said.

Could hit New Orleans
On its current path, forecasters said Isaac would hit Cuba and the southern tip of Florida before making landfall anywhere from the Florida Panhandle in the northwestern part of the state to Alabama and as far west as New Orleans.

A tropical storm warning was issued for the entire coast of south Florida on Friday, and a hurricane warning also went into effect in the Florida Keys.

Isaac has drawn especially close scrutiny because of the Republican Party's convention, a four-day meeting during which former Massachusetts Governor Mitt Romney will receive the party's presidential nomination.

Party officials insist the convention will go ahead, even if they have to alter the schedule. But NHC meteorologist Rick Danielson said Tampa could potentially be hit by coastal flooding and driving winds or rain.

"There is still a full range of possible impacts on Tampa at this point," he said.

Danielson said it was very hard to project intensity before Isaac passes over mountainous Cuba on Saturday and Sunday and enters the Florida Straits. But the Florida Keys, the island chain off the southernmost part of the state, were definitely in harm's way.

Reuters contributed to this report.

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Updated at 11 p.m. ET: Tropical Storm Isaac strengthened on Friday as its lashing rains took aim at flood-prone Haiti, but it was not expected to become a hurricane until it barreled into the Gulf of Mexico early next week. 

On its current path, forecasters said Isaac would hit Cuba and the southern tip of Florida before making landfall anywhere from the Florida Panhandle in the northwestern part of the state to Alabama and as far west as New Orleans.

Forecasters put the entire coast of south Florida under tropical storm watch as of 5 p.m. EDT (2100 GMT) on Friday.

But the biggest immediate concern was heavily deforested Haiti, where the U.S. National Hurricane Center (NHC) said the full force of the storm was expected to be felt later Friday.  

Isaac could pass near Florida's Gulf Coast early Monday just as the Republican National Convention is scheduled to start in Tampa. 

Winds at tropical storm strength extend 185 miles out from Isaac's center, the U.S. National Hurricane Center said in an afternoon advisory, making it a very wide storm.

On exiting Haiti, Isaac's center should cross Cuba on Saturday, and then pass south of the Florida Keys before making landfall as a Category 1 hurricane overnight Tuesday somewhere between New Orleans and Tallahassee, NBC meteorologist Al Roker said Friday on TODAY. Warm waters in the Gulf of Mexico will be "energy for the storm" as it makes its way across the gulf, he added.

In related developments Friday:

• The U.S. embassy in Haiti sent an e-mail to American citizens in the country warning that flights into and out of Port-au-Prince have been suspended due to Isaac.
• Oil and gas producers in the Gulf of Mexico started preparing as Isaac's track looked to skirt the heart of the U.S. offshore energy producing zone. BP said it would shut down its giant Thunder Horse platform, the world's largest. Royal Dutch Shell, Chevron and Apache Corp. said they would evacuate some workers from their Gulf platforms with no production impacts. Other offshore drillers were likely to shut production in coming days as the storm approaches.
• The U.S. military moved 22 F-16s from Homestead Air Reserve Base in Florida to Fort Worth, Texas. Three F-15s from the base are on alert to move to Jacksonville if necessary.

South Florida could see a few twisters and heavy rain -- some 5-10 inches Sunday and into Monday, weather.com experts said in an online chat with readers Friday.

Florida has not been hit by a major hurricane since 2005 and officials are concerned that residents there have become complacent.

Aid workers prep Haiti's tent city residents for Isaac's onlsaught

"I think it's a challenge of getting people to understand their risk and make sure they’ve got a plan," said Craig Fugate, administrator of the Federal Emergency Management Agency.

With more than 19 million people living across the Sunshine State, Fugate wants every Florida resident to have enough supplies to last 72 hours and to know when to evacuate.

Click this image to get to our Atlantic storm tracker.

"I think the most dangerous thing is when people keep waiting to see what the next forecast is even if they’re in an evacuation zone. They say, 'Oh, it’s just a Category 1 storm or a minimum hurricane.' We’ve seen significant impacts from tropical storm force winds and rain," Fugate added.

In the Florida Keys, where there are few routes available for evacuation -- U.S. 1, Key West International Airport, and the Florida Keys Marathon Airport -- Mayor Craig Cates said his biggest concern was the storm's timing. Cates said he would need at least 36 hours to begin evacuations of tourists and residents.

"If it (Isaac) comes straight on to Key West, we’re worried about the damage that could happen in Key West. If it goes further up the Keys, it could damage power lines and we could get affected," Cates said. "Even if it hits further up the state, we have got to be prepared with our generators and our supplies. Being on an island, we understand that."

Forecasters with The Weather Channel think the evacuation decisions could come quickly. It is anticipated that watches will be issued for South Florida and the Keys by Friday night. In the event of an evacuation, Cates told The Weather Channel that tourists would leave first, followed by special needs citizens. 

Live updates and analysis from weather.com
Transcript of weather.com experts answering Isaac questions 

Florida Gov. Rick Scott said state officials are working with convention organizers, who will ultimately make the call on a delay or cancellation of the event.

State officials announced Thursday that they will wait to make decisions about moving supplies until after Isaac passes Cuba. FEMA has already placed food and generators in Jacksonville.  

Isaac is forecast to remain a tropical storm after crossing the Dominican Republic and Haiti and then passing over Cuba into the Florida Straits.

The National Hurricane Center warned it was "important not to focus on the exact track because of forecast uncertainties and the fact that Isaac has a large area of tropical storm force winds."

Follow Isaac's path with our storm tracker

Isaac was expected to dump between 8 and 12 inches of rain over parts of Haiti and the Dominican Republic, and up to 20 inches in a few areas. That poses a significant threat to Haiti, which is highly prone to flooding and mudslides because of its near-total deforestation.

Haiti, the poorest country in the Americas, still has about 350,000 people living in tents or makeshift shelters more than 2-1/2 years after a devastating earthquake that took more than a quarter of a million lives.

Red Cross workers toured crowded tent camps of Haitians left homeless by the 2010 quake to warn about Isaac.

Authorities in the Dominican Republic evacuated people living on the banks of rivers, streams and areas vulnerable to landslides in preparation for the approach of Isaac, whose effects were beginning to be felt with showers in the south of the country.

Weather.com and Reuters contributed to this report.

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