Tropical Storm Colin picked up speed over the Gulf of Mexico on Monday as it headed toward Florida's northwest coast, unleashing thunderstorms and flooding while the state's governor activated the National Guard ahead of its landfall.

The storm, about 35 miles from the Florida coast as of 8 p.m. Eastern time, barreled toward land at 23 miles per hour, more quickly than it moved earlier in the day, the U.S. National Hurricane Center in Miami said.

The combination of the storm surge and high tides threatened flooding in coastal areas across the U.S. Southeast, with the storm expected to make landfall below Florida's Panhandle on Monday night.

A tropical storm warning was extended to the Outer Banks of North Carolina. On its forecast path, Colin would churn across southeastern Georgia early on Tuesday and later in the day menace the North and South Carolina coasts.

As Colin blasted 50-mile-per-hour winds at Florida, tornado warnings were issued across the state. The storm was forecast to dump as much as 8 inches of rain on parts of the state, the hurricane center said.

Florida Gov. Rick Scott, who had declared a state of emergency in 34 of the state's 67 counties, said more than 6,000 Florida National Guard members were activated and ready for deployment. Fast-moving squalls, tornadoes, flooding and property damage resulting from the fierce winds remained threats into the night, and far beyond the storm's immediate path, forecasters warned.

A statement from Scott's office warned residents to be wary of rip currents and the possibility of 10-foot waves along the Gulf Coast.

"It is critical that all Floridians use caution and remain alert," he said in the statement.

In the St. Petersburg beach town of Gulfport, roads were already flooded. One resident used a kayak to float down a thoroughfare past a waterfront cafe that stayed open, allowing people used to severe weather to witness the storm.

"This is a mild tempest," said Trace Taylor, a local writer lunching on onion rings. “What’s there to be afraid of? It’s just water and it’s not that bad."

More than 20,000 customers were without power ahead of the storm making landfall, local utilities reported.

The storm also threatened crops in Florida, the country's biggest citrus producer, which sent U.S. orange juice futures on Monday to their highest in more than two years.

Colin is part of a brisk start to the Atlantic hurricane season that runs through Nov. 30. Over the U.S. Memorial Day holiday weekend, the Carolinas were lashed by heavy rain and winds from Tropical Storm Bonnie.