Mexican officials prepare for rain threat as Tropical Storm Sonia heads for Pacific coast.

This NOAA satellite image taken Sunday, November 03, 2013 at 02:00 PM EDT shows Tropical Storm Sonia approaching the southern Baja Peninsula with maximum winds of 45mph. Low pressure system over the Northwest with areas of snow showers. Rain showers are seen over New Mexico. (AP PHOTO/WEATHER UNDERGROUND) (The Associated Press)

MEXICO CITY – Officials on Mexico's storm-struck Pacific coast braced for the possibility of heavy rains with the arrival of fast-moving Tropical Storm Sonia, which was projected to hit the mainland by early Monday.

The U.S. National Hurricane Center said Sonia was centered about 60 miles (96 kilometers) south-southwest of Culicacan late Sunday.

The storm had maximum sustained winds of 40 mph (65 kph), the same as earlier in the evening. It was heading north-northeast at 18 mph (29 kph).

Sonia could weaken some before coming ashore, and was likely to dissipate rapidly once over land, the center said.

Ismael Checa Landeros, civil defense director for Sinaloa, the state in the storm's path, said it was likely to hit near Culiacan, Navolato and Elota, all areas hit in September by Hurricane Manuel.

The government of Sinaloa state said school classes were canceled for Monday in five municipalities that could be affected by the storm. Sixty shelters were being opened in case anyone had to evacuate their homes.

Checa said officials were on alert but had not yet decided if anyone would need to be evacuated.

In the resort town of Los Cabos in Baja California, officials opened a shelter for possible evacuees and said the port had been closed to small craft.

The U.S. hurricane center said the storm could produce up to 6 inches (about 15 centimeters) of rainfall in Sinaloa and Durango states, with isolated areas getting as much as 10 inches (25 centimeters).