Forecasters with the National Weather Service in Miami also are expecting thunderstorms through the afternoon and evening. Other possibilities, rip currents, strong winds up to 60 mph, hail, flooding and waterspouts.
"Conditions are favorable for the formation of tornadoes," said CBS4 meteorologist Michael Smith.
Because of the rough weather, Miami-Dade school have canceled outdoor activities.
Principals are monitoring the weather radio for severe weather alerts and coordinating rainy day dismissal procedures.
CBS4's chief meteorologist Craig Setzer explains:
Everything is being spawned by an area of low pressure in the northern Gulf of Mexico that is helping to pump in moisture to the area. Mixing that with the unstable air and a cold front sweeping through the area and the ingredients for severe weather are set.
At least two periods of stormy conditions are expected today with spotty heavy thunderstorms developing after noon containing heavy rain and some hail.
The second band of activity will be a large squall line of storms with the possibility of damaging winds late in the afternoon and evening. There will be a threat of brief tornadoes with the heaviest storms this afternoon.
The overall storm direction of the first round will be from southwest to northeast while the squall line will race from the west coast across South Florida.
Rain chance is 70 percent on Thursday. Rain chance will decrease to 50 percent on Friday and turn sunny and cooler on Saturday.
Information on the tornado watch can be found on the National Weather Service advisories.