Thunderstorms covered the Dominican Republic. Rivers burst their banks in dangerously deforested southern Haiti, where gusts uprooted a palm tree and flung it into a mud hut, injuring two people who were hospitalized in southern Les Cayes town.
Dennis grew to a Category 2 hurricane Thursday morning, becoming the third storm to threaten petroleum output in the Gulf of Mexico. Private forecaster AccuWeather put the storm right into U.S. oil and gas producing facilities.
Oil futures rose sharply Wednesday on concerns about Dennis but were down nearly $2 Thursday morning at $59.35 a barrel, as a series of terrorist blasts in London led investors to abandon riskier investments.
The hurricane follows Tropical Storm Cindy, which made landfall late Tuesday in Louisiana and hindered oil production and refining. On Thursday, remnants of Cindy hit parts of the Carolinas, prompting flash flood and tornado watches.
The Cayman Islands were on hurricane watch, and the southern Florida peninsula was on tropical storm watch, expecting severe conditions within 36 hours. Forecasters at the U.S. Hurricane Center in Miami said the storm could strike the United States on Sunday or Monday.
"It is possible that Dennis may become a major hurricane," the center warned.
Lead forecaster Martin Nelson said it was the first time the Atlantic hurricane season had four named storms this early since record-keeping began in 1851. The season runs from June 1 to Nov. 30.
By Thursday morning, Dennis's sustained wind reached nearly 105 mph with higher gusts, the U.S. National Weather Service said. The storm, the first hurricane of the Atlantic season, could dump 20 inches of rain over mountains in its path, including Jamaica's coffee-producing Blue Mountains, forecasters said.
Tropical storm force winds from Dennis's outer bands had already reached eastern Jamaica. "Regardless of landfall, Jamaica will have impacts ... practically all day and into the evening hours," warned forecaster Dave Roberts of the U.S. National Hurricane Center in Miami.
Last year, hurricanes Frances, Ivan and Jeanne tore through the Caribbean with a collective ferocity not seen in many years, causing hundreds of deaths and billions of dollars in damages.