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By Alex Johnson

A tropical depression prosaically named "No. 9" was expected to strengthen into a tropical storm and rake across central Florida's Gulf Coast later this week, forecasters said Tuesday.

Nine's maximum sustained winds were near 35 mph Tuesday evening as it swirled in the middle of the Gulf of Mexico. But it's expected to become a tropical storm later Tuesday night or early Wednesday, the National Weather Service said.

The weather service said early indications were that the system will make landfall Thursday night or early Friday somewhere between Tampa and Cape San Blas. Cape San Blas is on Saint Joseph Bay midway through the Panhandle, about 45 miles southeast of Panama City Beach.

Tropical Depression 9 is expected to make landfall Thursday night or early Friday between Tampa and Cape San Blas, Fla.National Hurricane Center

A hurricane watch was issued Tuesday afternoon for the Gulf Coast from the Anclote River to Indian Pass in Florida. A tropical storm watch was in effect from west of Indian Pass to the Walton/Bay County line.

At the moment, the system isn't projected to top out as much more than a fairly strong tropical storm, with maximum winds of about 60 mph, said Ari Sarsalari, a meteorologist for The Weather Channel.

But that's still enough to generate "some storm surge, some rain issues and also, of course, some wind damage," Sarsalari said — and thunderstorms were already arriving on the coast from the system's extreme northern and eastward reaches Tuesday afternoon.

Two people suffered minor injuries when lightning struck a building they were leaning against in Tampa, NBC station WFLA reported, while some street flooding was reported in Key West.

Drivers make their way in the rain Tuesday along Interstate 95 in Miami.Wilfredo Lee / AP

In Collier County, the Naples Pier was closed for time Tuesday afternoon because of heavy rain, wind and reports of hail, NBC station WBBH of Fort Myers reported. The sheriff's office reported significant street flooding in East Naples and urged motorists to drive with extreme caution.

Meanwhile, Duval County Public Schools canceled all after-school activities for Thursday because of the approaching storm.

Gov. Rick Scott urged people all along the Gulf Coast to make sure they had plenty of food, water and medicine on hand.

"Don't wait until after it happens," Scott said at a news briefing, where he announced that 8,000 National Guard members are on standby in case they're needed.

Residents fill sandbags Tuesday in Hillsborough County, Fla., ahead of the arrival of Tropical Depression 9.WFLA-TV via NBC News Channel

"Hopefully, we will not have a hurricane this season, knock on wood," the governor said. "But we are going to have storm surges, we are going to have flooding, we have the potential of tornadoes, and we're going have rip currents.

"Everybody has to be prepared," he stressed.

Only a few hours earlier, the thinking had been that the storm would be the second punch of a Labor Day Weekend double whammy, because first Florida and the Carolinas would have to deal with Tropical Depression 8 out in the Atlantic.

Related: Labor Day Weekend Washout Feared for North Carolina Coast

But Eight was drifting away from North Carolina's Outer Banks on Tuesday evening, the National Hurricane Center said, and by 8 p.m. ET, all advisories connected to it had been canceled.

"The storm has made that turn and is heading back out to sea with what, I think, will be minimal impacts," said Greg Fishel, chief meteorologist for NBC station WRAL of Raleigh, N.C.