SAN JUAN, Puerto Rico – Tropical Storm Isaac churned toward the Dominican Republic and Haiti on Thursday, threatening to strengthen into a hurricane that could take a shot at Florida just as the Republicans gather for their national convention.

The storm dumped heavy rain across eastern and southern Puerto Rico and whipped up waves as high as 10 feet in the Caribbean as it moved through the region.

U.S. forecasters said Isaac could become a Category 1 hurricane Friday as it approaches the island of Hispaniola, which is shared by the Dominican Republic and Haiti. It was expected to weaken a little while crossing over Haiti and the eastern two-thirds of Cuba.

The storm was projected to head toward Florida as a hurricane by Monday, but the U.S. National Hurricane Center in Miami said some forecast models predict it could go farther west into the Gulf of Mexico, so “significant uncertainty remains about the threat Isaac poses to Florida.”

Isaac was centered 180 miles south-southwest of San Juan, Puerto Rico, Thursday afternoon, with maximum sustained winds of 40 mph. It was moving west-northwest at 16 mph, according to the hurricane center.

Haitian Prime Minister Laurent Lamothe urged people to avoid crossing rivers and to tape their windows, and said they should ask relatives overseas to wire money so they can stock up on food and water.

Above all, he said, it was important to stay calm. “Panic creates more problems,” he said.

Lamothe and other officials in Haiti, which is prone to flooding, said the government has set aside about $50,000 in emergency funds and that it had buses and 32 boats on standby for evacuations.

While Haiti’s government spent the day preparing for Isaac, others did not because they didn’t have the means. The notion of preparation in a country where the bulk of the population gets by on about $2 a day was met with a shrug.

“We don’t have houses that can bear a hurricane,” said Jeanette Lauredan, who lives in a tent camp in the crowded Delmas district of Port-au-Prince.

About 400,000 people remain in settlement camps that are mere clusters of shacks and tarps as a result of Haiti’s devastating 2010 earthquake.

Isaac also posed a threat to next week’s Republican National Convention in Tampa, where 70,000 delegates, journalists and protesters are expected.

Convention officials said they were working closely with state and federal authorities on monitoring the storm.

“We continue to move forward with our planning and look forward to a successful convention,” convention CEO William Harris said in a statement.