Tropical storm Raymond neared hurricane strength as it swirled towards Mexico's Pacific coast on Sunday, threatening to dump heavy rain on the beach resort of Acapulco, which is still recovering from destructive floods last month.
The Miami-based National Hurricane Center said Raymond was expected to become a hurricane later on Sunday, and Mexico has issued a tropical storm watch from Acapulco in Guerrero state to the port of Lazaro Cardenas further northwest.
Raymond is likely to get close to the coast late on Monday or on Tuesday, then begin to meander, the NHC said.
Mexico has no major oil installations in Raymond's path.
Mexico suffered its worst flooding on record when tropical storms Manuel and Ingrid converged from the Pacific and the Gulf of Mexico in mid-September, killing more than 150 people and causing estimated damage of around $6 billion.
The Mexican government said it was monitoring conditions closely from the state of Chiapas in southern Mexico to Jalisco in the west, and that local authorities were ready to evacuate people from vulnerable areas if necessary.
Over the next few days, Raymond may cause life-threatening flash floods and mudslides, the NHC said.
Up to 15 cm (6 inches) of rain could hit the coast, Mexico's national meteorological service (SMN) forecast.
Complicating matters for Mexico is a cold weather front currently in the Gulf of Mexico off the state of Veracruz that could interact with Raymond to intensify the flood risk. SMN said the cold front could produce up to 5 cm (2 inches) of rain in northeastern, eastern and central parts of the country.
Acapulco was one of the places worst hit by last month's chaos, as torrential rains put the city's airport under water and stranded thousands of tourists.
The flooding, landslides and displacement of thousands of people caused by the storms have also heightened the risk of diarrheal illness. Mexico is experiencing its first local transmission of cholera in just over a decade.
Over the past seven weeks, more than 170 cases of cholera have been confirmed in the country, including one death.
By mid-afternoon on Sunday, Raymond was churning about 155 miles (250 km) southwest of Acapulco and moving north-westward at about 6 mph (10 kph). The storm was generating maximum sustained winds of 70 mph (113 kph) with higher gusts, the NHC added.