Coming right behind Tropical Storm Cindy, which made landfall late Tuesday in Louisiana, Dennis has helped push oil and gas prices sharply higher.
Packing sustained winds near 70 mph, the second storm of the Atlantic season could dump up to 10 inches of rain over mountains in its path, including Jamaica's coffee-producing Blue Mountains, according to the U.S. National Hurricane Center in Miami.
"It is a minimal hurricane right now" though its winds were four mph under the official hurricane strength, said the hurricane center's lead forecaster Martin Nelson.
Heavy rain and a storm surge flooded low-lying streets along the Gulf Coast on Wednesday as a weakening Tropical Storm Cindy pushed inland, leaving more than a quarter-million homes and businesses from Louisiana to Alabama without electricity.
Cindy's top sustained winds had weakened from 50 mph to 35 mph by midmorning and it was downgraded to a tropical depression. It was expected to continue its decline while pushing through Alabama, said the National Hurricane Center in Miami.
Cindy's sustained winds earlier of 70 mph brought squalling rains and heavy downpours, reports Dave Cohen of CBS radio affiliate WWL-AM. Thousands of people were left with no electricity. Throughout metropolitan New Orleans, trees and power lines were down and debris was scattered.
But it was water that caused problems in Mississippi's coastal Hancock, Harrison and Jackson counties.
"We have recorded 3 to 4 inches of rain and we have a storm surge of 4 to 6 feet above normal tide. We have a number roads that flooded with rain water that presents a travel hazard," said John Edwards, a spokesman for the Harrison County emergency operations center.
Officials said the high water affected only areas that normally are prone to flooding.
By midmorning Wednesday, officials in Mississippi's coastal counties said water was draining from flooded streets and low-laying areas.
Fishermen returned to boats along the coast Wednesday but were already keeping watch on the next weather system, Tropical Storm Dennis.
Dennis, a larger and more powerful storm, could hit Florida as early as Friday, reports CBS News Correspondent Lee Cowan, and forecasters say it could well head back into the Gulf of Mexico and make a beeline for Louisiana and Mississippi early next week.