Hurricane Rina weakened Wednesday but held its course for a direct hit on Mexico's tourist beaches, where evacuation orders were issued for vulnerable coastal areas.

Residents reinforced windows and 1,000 emergency shelters were set up in preparation for Thursday evening when Rina is expected to come crashing ashore over tourist hotspots such as Cancun, Playa del Carmen and Cozumel.

Cuba was also being urged to prepare for high winds and heavy rains over the weekend as Rina curls off northward into the Caribbean.

The Miami-based National Hurricane Center said Rina had "significantly weakened" with maximum sustained winds of 85 miles (135 kilometers) per hour, as opposed to 110 miles (175 kilometers) per hour overnight.

Now only a category one storm on the five-point Saffir-Simpson scale, US experts said they expected it to weaken further before making landfall on Thursday night.

NHC spokesman Dennis Feltgen told AFP that "the storm may have peaked," but warned that Rina remained "dangerous" and could still cause fatalities and destruction.

The US State Department has warned Americans living or on vacation in the area to prepare for the storm, and perhaps consider leaving Mexico as flights could be disrupted once the storm starts to bear down.

"Identify local shelter, monitor local media reports, and follow the instructions of local emergency officials," it said in a travel warning.

"In some areas, adequate shelter from a severe hurricane may not be available to all who choose to stay."

A Nicaraguan naval vessel that disappeared on Sunday with 29 people on board during an evacuation mission ahead of the storm was found on Tuesday with all occupants "safe and sound," officials said.

Nicaraguan President Daniel Ortega had ordered the ship to remove people from flood-prone coastal areas, but contact was lost after four sailors had picked up 25 indigenous Miskito fishermen.

Rina is the sixth hurricane and 17th named storm of the Atlantic hurricane season, which runs from June 1 to November 30. After passing near or over Mexico's Yucatan, it is forecast to weaken as it spins toward Cuba and Florida.

Feltgen said Florida was not likely to be hit hard as the storm could peter out by the time it nears the US mainland.

US space agency NASA was taking no chances and evacuated a crew of astronauts from an underwater lab off the coast of Florida where they were training for a possible trip to an asteroid.