The U.S. Gulf Coast was under threat from Tropical Storm Isaac Sunday afternoon after it drenched the Florida Keys and was strengthening, forecasters said. After sweeping Haiti, where at least three people were killed, and then dousing Cuba, at 2 p.m., Isaac was 50 miles south-southeast of Key West, moving west-northwest at a quick 16 mph. It had sustained winds of 60 mph that extended 205 miles from the center, the National Hurricane Center in Miami said. \"Some strengthening is forecast during the next 48 hours, however the likelihood of Isaac becoming a hurricane before it reaches the Florida Keys is decreasing\" the forecast said. Computer models suggest Isaac will hit the western Florida Panhandle Tuesday as a Category 2 hurricane with sustained winds of at least 96 mph near Panama City, AccuWeather.com reported.. Hurricane watches were extended earlier in the day northward along the Gulf coast as far as New Orleans, the forecasters said. Coastal storm surges coupled with tides could produce sea levels as much as 7 feet above normal, the center said. The center said as much as 12 inches of rain could deluge the Keys Sunday and also warned of dangerous surf and rip current conditions. \"Tornadoes are possible today over central and southern Florida, with the greatest threat over southern Florida and the Keys,\" the center said. Keys emergency management officials in Monroe County issued an appeal for residents and tourists to respect the dangers Isaac will pose. \"You\'ve chosen to remain in the Keys during this storm and the only safe place for you to be is indoors,\" Emergency Management Director Irene Toner said. \"Stay off roads and don\'t go outside.\" The county announced municipal offices, courts and schools would be closed Monday. Elsewhere, organizers of the Republican National Convention in Tampa announced Saturday the convention activities Monday were canceled and events would begin Tuesday because of Isaac\'s threat. Heavy rain was expected to begin in the Tampa area Sunday and gusty winds would begin early Monday, the National Weather Service said.