Tropical Storm Ernesto picked up strength on Monday in the Caribbean and was expected to reach hurricane force later in the day, threatening the coasts of Belize and Mexico, US weather forecasters said.
The Miami-based National Hurricane Centre (NHC) said Ernesto was packing winds of 105km per hour winds as it powered across the Caribbean toward Central America.
"Strengthening is forecast and Ernesto could become a hurricane by tonight," the center said in a 1500 GMT bulletin. "Ernesto could become a hurricane by tonight."
It said a hurricane watch was in effect for the entire coast of Belize, while parts of the Yucatan Peninsula's east coast were under a hurricane warning. The Mexican beach resort of Cancun, located further north on the Yucatan peninsula, was under a tropical storm watch.
Ernesto was expected to pass north of the coast of Honduras late on Monday and Tuesday and then reach the east coast of the Yucatan early on Wednesday.
The NHC warned that the storm would trigger a "dangerous storm surge" where it makes landfall, raising water levels by up to 1.2m above normal tide levels.