The state braced for flooding, with Florida Gov. Rick Scott declaring a state of emergency early Monday. Rains also pounded southern Georgia and South Carolina.
It is near the Big Bend area of Florida, the National Hurricane Center said. That region includes Florida Panhandle counties east of the Apalachicola River.
"It's a highly disorganized storm, primarily a rainmaker," CNN senior meteorologist Taylor Ward said.
It is expected to race along the U.S. East Coast, pounding the Carolinas as it heads northeast Tuesday, Ward said.
By Wednesday afternoon, forecasters said, the storm will be in the Atlantic Ocean.
"We're looking at another 24 hours of heavy rain from Florida to the coastal Carolinas before it heads out to sea," Ward said.
Colin is about 35 miles south-southeast of Apalachicola, Florida, according to the latest update from the National Hurricane Center.
It is packing maximum sustained winds of 50 mph and moving north-northeast at 23 mph.
The Florida National Guard is ready to deploy up to 6,000 people to areas affected by Colin, the governor said. The state also has a 250-person team responding to road closures and directing traffic during power outages. Parks, schools and camp activities have been closed, and state agencies are closely monitoring infrastructure and conditions.
Flash flooding fears
The rainfall could be welcome news for some as the storm replenishes aquifers in the state that have been low on water, CNN meteorologists said.
"Some of this rain could be 6 inches deep. Now many of these areas have been dry, so we'll take the rain," CNN meteorologist Chad Myers said. "You just don't want the flooding with this."
That's something to watch out for, forecasters from the hurricane center warned.
"The combination of a storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters," the center said.
Heavy rainfall could cause flash flooding, Myers said, as the storm moves across Florida, southern Georgia and South Carolina.
Tropical storm warnings are in effect from Indian Pass to Englewood, Florida, on the Gulf and from the Sebastian Inlet in Florida on the Atlantic to Oregon Inlet, along North Carolina's Outer Banks.
Making the best of it
As the storm started to roll in Monday, Cliff York and his family leaned over a wall at their beach hotel in Clearwater to take in the scene.
This isn't what they had in mind when they left Vincennes, Indiana, for a Florida vacation.
"Sounds like the weather is better in Indiana than it is here," York joked. "Maybe we just should have stayed there."
But York said they'll still find a way to relax.
"We got two sunny days in Orlando," he said. "Now we have to make the best of what we can while we're here."
Dylan Fagan, who lives in Fleming Island, Florida, near Jacksonville, said the rain came out of nowhere and blew through really quickly. He picked up this children early from day care Monday as a precaution.
Earliest third storm on record
Colin is the third tropical storm to form this year in the Atlantic. It's the earliest that three named storms have hit the region, besting the previous record -- which was set in 1887 -- by about a week.
Hurricane season officially began June 1
. But tropical systems can form during any month of the year.
This year, two named storms formed before the season's official start.
became a named storm on January 13, the first Atlantic hurricane to form in the month of January since 1938.
drenched South Carolina's coast last month.
Does it mean anything to see storms forming so early?
Not necessarily, forecasters say.
"These first three storms have been very weak systems, even though Bonnie produced a lot of rain in South Carolina," CNN meteorologist Tom Sater said. "This really means very little when it comes down to how this year may turn out."