This NOAA satellite image shows shower and thunderstorm activity developing around an area of low pressure spinning in the Gulf of Mexico
A tropical storm warning was issued Sunday for Alabama to the Florida Panhandle as Debby lashed parts of the Gulf Coast with wind and rain.
The National Hurricane Centre in Miami said Sunday morning that Debby was about 190 miles (310 km) east-southeast of the mouth of the Mississippi River. It said the storm warning has now been issued from the Mississippi-Alabama border eastward to the Suwanee River in north Florida, reports The Associated Press.
Debby's top sustained winds had increased to about 60 mph (95 kph). The storm was moving toward the northeast at 6 mph (9 kph).
Although a forecast track was still uncertain, the hurricane centre said people from Texas to Florida should remain alert to Debby's movement.
At least one tornado linked to the storm touched down Saturday in southwest Florida, but no injuries were reported. Heavy squalls pounded parts of that state. However, despite warnings in the Panhandle, Debby hadn't totally dampened vacations.
Thousands of people were on the beach at Pensacola Beach, Fla., on Sunday morning. Many used their phones to take photos of huge waves crashing into the concrete supports of a fishing pier. There wasn't any rain yet; just gusty winds and dark, fast-moving clouds.
Few people were in the water. Red flags warned tourists to stay out of the surf, and lifeguards cruised the sand on all-terrain vehicles, blowing whistles at anyone who got near the waves.
Workers with rental companies used pickup trucks to gather chairs and umbrellas as a precaution against an unusually high tide.
Forecasters said Debby could reach hurricane strength sometime over the next few days. Meanwhile, up to 10 inches of rain were possible along the coast, with isolated amounts possibly reaching 15 inches.
It was the first time four tropical storms have been recorded before July 1 during the Atlantic hurricane season since record keeping began in 1851. Alberto was the first storm this year. It formed off the South Carolina coast on May 19, almost two weeks before the hurricane season officially began June 1.
Debby forced the suspension of 8 percent of the region's oil and gas production.