Tropical Storm Colin churns toward Florida

Experts: Storm has maximum sustained winds of 40 mph

Just days after the official start of hurricane season, a tropical storm is churning toward the Florida coast.

Officials on Sunday warned that the cyclone, which is currently located about 460 miles (735 kilometers) southwest of Tampa, Florida, had strengthened from a tropical depression into a tropical storm.

A U.S. Air Force reserve unit "hurricane hunter" aircraft determined the storm had maximum sustained winds of 40 mph, the National Hurricane Center said.

It's heading north at about 9 mph, forecasters said.

The storm is expected to make landfall Monday, but already it's threatening to bring heavy rainfall over portions of the state, the hurricane center said.

That could be welcome news for some as the storm replenishes aquifers in the state that have been low on water, CNN meteorologist Tom Sater said.

Flooding is also possible.

"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.

Earliest third storm on record

Colin is the third tropical storm to form this year in the Atlantic. And it's the earliest third storm on record to form in the Atlantic Basin.

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.

Alex became a named storm on January 13, the first Atlantic hurricane to form in the month of January since 1938.

Bonnie 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," Sater said. "This really means very little when it comes down to how this year may turn out."