MIAMI - Late-season Tropical Storm Otto is strengthening in the southwest Caribbean and forecasters say it could become a hurricane in the next few days.

The U.S. National Hurricane Center in Miami said the storm had top sustained winds of 60 mph (95 kph) Monday night and was moving south at 2 mph (4 kph) about 210 miles (335 kilometers) east-southeast of San Andres Island, Colombia.

The center says the government of Colombia has issued a tropical storm watch for San Andres Island.

Forecasters say more strengthening is expected and hurricane status could be reached Tuesday. They also say heavy rains associated with the storm could fall in Panama and Costa Rica later this week.