Debby updates: Flash flooding, tornadoes target DC, Mid-Atlantic, Northeast

While still a tropical storm, Debby is nearing hurricane strength, producing maximum sustained wind speeds up to 70 mph.

Debby will continue to intensify rapidly overnight as it travels northward over the Gulf's warm waters. It is forecast to become a hurricane tonight. It is expected to strengthen to at least a strong Category 1 hurricane before making landfall along Florida's Big Bend region Monday morning (around 7 a.m. ET), producing sustained wind speeds near 85 mph and wind gusts reaching over 100 mph possible.

Located about 90 miles southwest of Cedar Key, Florida, the storm continues to impact the Florida Gulf Coast with heavy rainfall, storm surge, powerful winds and even spin-up tornadoes.

A reported wind gust of 56 mph was reported in St. Petersburg, with two tornadoes reported in central Florida.

A 60-mph wind gust was also reported near Sarasota, Florida.

Numerous reports of flooding from heavy rainfall and surges have also been submitted up Florida's Gulf Coast.

The Tornado Watch covering much of northern and central Florida and southern Georgia has been extended until 6 a.m. ET on Monday.

Once Debby moves over land, it will weaken. However, the lack of a steering current will cause the storm to slow down considerably. While its exact track remains questionable, model guidance suggests the storm will drift over the Atlantic or Southeast coastline late Monday night into Tuesday before meandering back over Georgia and the Carolinas. Interaction with the Atlantic could reenergize Debby, but that will greatly depend on the storm's path.

Even though Debby's track and timing remain uncertain later this week, there is high confidence that it will bring historic rainfall and significant flooding across portions of the Southeast.

Rainfall ranging between 6 to 12 inches is possible from Florida's Big Bend region through southeastern Georgia and into the Carolinas. Parts of coastal Georgia and South Carolina will be in the bullseye for the heaviest rainfall. There, widespread totals between 10 to 20 inches are possible, with some places even seeing up to 30 inches locally. Because of this, significant urban and river flooding is anticipated.

Rainfall aside, hurricane and tropical storm force winds will continue to whip across Florida and will likely intensify Sunday night into Monday as the storm moves closer to the coast -- with areas just south and east of the storm's eyewall seeing the strongest gusts early Monday morning.

Storm surge will also worsen along Florida's northern and central Gulf coast tonight into Monday morning, with the highest surge expected between Suwannee River and Ochlockonee River (6 to 10 feet).

All tropical alerts remain unchanged from the last update.

-ABC News meteorologist Shawnie Caslin Martucci

As of 5 p.m. ET on Sunday, Tropical Storm Debby still has winds of 65 mph and is forecast to undergo rapid intensification into a hurricane overnight, according to the National Hurricane Center.

Debby is expected to make landfall as a hurricane in Florida’s Big Bend region on Monday morning around 7 a.m.

Rain is expected to be the most impactful element from this storm, affecting a wide area over an extended period of time.

"Across portions of southeast Georgia and South Carolina, 10 to 20 inches of rainfall, with local amounts to 30 inches, are expected through Friday morning," the National Hurricane Center said. "This potentially historic rainfall will likely result in areas of catastrophic flooding."

An evacuation order was issued Sunday for residents of Alachua County, Florida, residing in mobile homes, manufactured homes and recreational vehicles ahead of the arrival of Debby, which is forecast to be a hurricane when it makes landfall on Monday.

People living in areas close to rivers and lakes, and low-lying areas that tend to flood in Alachua County are also encouraged to evacuate, according to a statement issued by county officials.

Gainesville is the largest city in Alachua County

"We encourage residents affected to find alternative housing with friends, family or short-term rentals," according to the county's statement.

Alachua County is opening three shelters for residents in need.

-ABC News' Bill Hutchinson

A tornado watch was issued Sunday afternoon by the National Weather Service as Tropical Storm Debbie moved northward in the Gulf of Mexico parallel to Florida's Gulf Coast.

At 2 p.m. Sunday, the National Hurricane Center said Debby was still a tropical storm with winds of 65 mph and forecasted to bring severe weather, including heavy rain, to coastal communities Sunday afternoon.

A tornado watch is in effect for much of Florida through Sunday evening.

Debby is expected to become a hurricane Sunday evening and will likely make landfall sometime between 7 a.m. and 8 a.m. Monday in the Big Bend area of Florida's Panhandle.

Once Debby makes landfall, the storm is expected to slow down and essentially stall over the Southeast, dropping potentially historic amounts of rainfall as it moves into Georgia and South Carolina.

A hurricane warning is in effect for the west coast of Florida from the Ochlockonee River southwest of Tallahassee to the Suwannee River northwest of Gainesville.

-ABC News' Daniel Amarante