Thousands of people in Mexico, Cuba and Florida are leaving their homes to escape from Hurricane Wilma.
Wilma, which still carries lashing rain and winds of 155mph, was the strongest hurricane ever recorded. It has now weakened to a Category Four.
At least 11 people have been killed in Haiti by floods and landslides.
The storm's barometric pressure, which is a measure of its strength, was the lowest ever on record in the area known as the Atlantic basin.
The lower the barometric pressure at the centre of a hurricane, the stronger the storm.
The US National Hurricane Center expects the storm to dump up to 63cm of rain in mountainous areas of Cuba until Friday.
Mexican authorities have told tourists to leave high-risk areas along its coast, and Honduras and Nicaragua have also issued alerts.
Forecasters say the storm could hit Florida this weekend, where it could do a lot of damage.