Isaac is expected to hit the Lower Florida Keys on Sunday night as a tropical storm, packing possible 65 mph winds and torrential rains, which could cause flooding throughout the southern tip of the island chain.

The storm will hit the Keys between 8 p.m. and midnight, National Weather Service metrologist Bill South said. Winds are expected to be between 39 and 65 mph.

There is also an 18 percent chance the storm could whip into a Category 1 hurricane if it skirts the northern coast of Cuba and doesn't make landfall there; a scenario that would likely push the storm more eastward where it could strike the Upper Keys, South said.

Six to 10 inches of rain was expected to drench the Keys while the storm passes, South said.

A tropical storm watch was issued at 5 p.m. Friday for the Keys.

The high tide Sunday is at 7:32 p.m., which could add to flooding headaches, but as of Friday evening forecasters were more concerned about flooding due to torrential rainfall than by tidal surges, South said.

"We want everybody done with their shopping and storm preparations by Saturday night, so they can hunker down and safely ride it out Sunday," South said.

Earlier models had the storm taking a more westerly path and passing Key West to the west, but Friday disagreements arose among forecasters over two models that had the storm taking different paths.

Tourists will not be ordered to leave the Keys, "unless there is a drastic change in weather," said County Administrator Roman Gastesi Friday evening, after a meeting of the emergency management team.

Shelters will open at 2 p.m. today, said Gastesi: Key West High School, Stanley Switlik Elementary in Marathon and Coral Shores High School in Tavernier.

There may be power outages if lines are downed. Keys Energy Services crews will remain working in the field until sustained winds reach 35 mph, at which point all crews will be removed from the streets. If power outages occur after this time, the utility will not attempt to restore power. All restoration will take place when the storm has passed. Essential utility employees will be on standby to begin the restoration process immediately after winds subside.

After the storm, Keys Energy crews will survey affected areas to assess the damage and determine the equipment, materials, and personnel necessary to restore power. Utility crews will then begin the restoration process. To assist in this process, the utility company has a number of contracts and agreements in place to mobilize emergency supplies and additional crews from other utilities.

While tourists and residents were not ordered from their homes and hotels, dogs and cats from the Florida Keys SPCA shelter on Stock Island did find temporary new homes. The animals will stay with local residents until the weather clears.

Shelter staff on Friday had placed 84 cats and 44 dogs since starting on Thursday, said shelter director Tammy Fox.

"It's the community; we started putting out pleas," said Fox, crediting Key West residents for the quick fix.

The College Road shelter has a flood risk and simply isn't safe, said Fox. The agency has been collecting donations for a new shelter for years.

"We don't know how sturdy the concrete walls are either," Fox said. "We wants a shelter that's floodproof and can withstand Category 5 winds. We could take animals for first responders so they don't have to worry about their pets."

The Marathon Turtle Hospital remained in a holding pattern on Friday.

"We will not move the turtles because it's too stressful to do that until a mandatory evacuation is called," said Richie Moretti, hospital founder. "If Monroe County does a mandatory evacuation for tourists, at that point we close the gift shop and educational programs, put on all storm shutters and we move all turtles."

After surviving Wilma's storm surge in 2005, Moretti installed two 30,000-gallon tanks directly behind the hospital for the turtles.

"We've never lost any turtles," said Moretti, who will ride out the weather at the hospital, where 23 turtles live, including one that weighs in at 400 pounds.

The Florida Keys received a small taste Friday of what Sunday might be like.

The National Weather Service issued a severe weather alert and special marine warning for the Lower Keys Friday morning.

The National Weather Service reported 50 mph wind gusts on Duck Key and 34 mph wind gusts in Marathon. There were also severe wind gusts reported on Big Pine Key. The conditions were favorable for waterspouts and small tornadoes, but none were reported.

The weather pattern moved quickly across the Keys, Parker said. Officials were not sure if it was related to Tropical Storm Isaac.

Lower Keys Medical Center said Friday that all of its services, including the emergency room, remain open. Surgeries have not been canceled so far. Hospital ER staff urged residents to use extra caution when preparing homes and boats for the storm.

Key West International Airport will close Saturday night, said Gastesi.

This story was reported and written by staff writers Adam Linhardt, Timothy O'Hara and Gwen Filosa.