Bracing for high winds, strong waves and downpours, Acapulco, the biggest city in the southwestern state of Guerrero, closed its port, and school classes were suspended in the state for Monday, local government authorities said.
Shelters for people at risk from the rainfall were opened, and the advancing weather front knocked down trees and fences in parts of the state, authorities added.
Acapulco's airport was still open on Sunday afternoon.
Meanwhile on the other side of the country, a low pressure system in the Gulf of Mexico that could become a tropical storm in the next two days was producing showers on the coast of Guatemala, Belize, and Mexico's Yucatan peninsula, the NHC said.
By mid-afternoon Carlos was 121km west-southwest of Acapulco, blowing maximum sustained winds of 113kmh with higher gusts, and moving northwest at around 10kmh), the Miami-based center said.
Carlos was a Category 1 hurricane on Saturday, but was downgraded to a tropical storm after weakening overnight. By Monday, Carlos is expected to become a hurricane again.
The NHC projections showed it could hit the coast near the industrial port of Manzanillo by Tuesday morning, before moving toward the tourist resort of Puerto Vallarta the next day.
Rain from Carlos is expected to fall in the states of Oaxaca, Guerrero, Michoacan, Colima and Jalisco, with 15 inches (38 cm) possible in some areas through Tuesday, the center said.
A hurricane watch was in effect from Punta San Telmo to Manzanillo, with storm warnings also out in Guerrero.
