MEXICO CITY (AFP) - Carlos gathered hurricane strength off the Mexican Pacific coast on Saturday, as it threatened to lash the region with heavy rain.
The Category 1 storm on the five-point Saffir-Simpson scale was located about 225km south of Acapulco, the US National Hurricane Centre reported.
At 1500 GMT, it was moving northwestward at just 4kmh.
Luis Felipe Puente, head of the national civil protection service, said it was unlikely the storm would reach Category 2 strength.
The Mexican government has issued a hurricane watch from Lazaro Cardenas to Punta San Telmo and a Tropical Storm Warning from Tecpan de Galeana to Lazaro Cardenas.
Puente said authorities were on alert for heavy rains and high waves in the states of Oaxaca, Guerrero and Michoacan.
Guerrero was the worst hit region in September 2013 when twin hurricanes Ingrid and Manuel almost simultaneously struck both coasts of Mexico, leaving 157 people dead.
Carlos is the third hurricane of the Pacific storm season, following Andres, which never made landfall, and Blanca, which weakened to a tropical storm when it reached Baja California peninsula on Monday.