A blizzard slammed into the northeastern United States on Friday, snarling traffic, disrupting thousands of flights and prompting five governors to declare states of emergency in the face of a fearsome snowstorm.

As Tropical Storm Isaac continued to churn out of eastern Cuba, forecasters from the National Hurricane Center issued a hurricane warning Saturday for the Florida Keys, the Gulf Coast from Bonita Beach south to Ocean Reef, and Florida Bay. The storm is expected to approach Sunday as a Category 1, 75- to 80-mph hurricane across the Lower Keys and Florida's southwestern tip.

Tropical Storm Isaac formed in the Atlantic Ocean and churned toward the Caribbean Sea on Tuesday afternoon, and it could become a Category 1 hurricane by Thursday, forecasters at the National Hurricane Center said. Late Tuesday afternoon, Isaac was 500 miles east of Guadeloupe in the Leeward Islands and moving west at 17 mph.

Hurricane Ernesto came ashore on Mexico's Caribbean coast near the border with Belize late Tuesday, after hundreds of tourists left beach resorts and fishermen abandoned low-lying villages to avoid the threat of damaging rain and wind. Ernesto had sustained winds of 85 mph (140 kph).