MEXICO CITY: Tropical Storm Cristobal is creeping along just inland over Mexico's Gulf coast state of Campeche, threatening to cause flooding the next few days before a predicted turn northward toward the US.

The storm's sustained winds weakened to 45 mph (75 kph) after it moved inland Wednesday near the oil town of Ciudad del Carmen. The US National Hurricane Center said it was expected to weaken into a tropical depression by Thursday, but then begin strengthening once it moved back over the Gulf of Mexico on Friday.

Cristobal was forecast to be out in the central Gulf on Saturday and could be nearing the U.S. Gulf Coast by Sunday, the hurricane centre said. It added that current conditions "will not be very conducive" for further strengthening as the storm moves away from Mexico.

The Mexican army evacuated 138 people in Campeche after floodwaters threatened homes, and police in Campeche reported water washing across highways.

By late Wednesday, the storm was nearly stationary about 20 miles (35 kilometres) south of Ciudad del Carmen.

Cristobal formed Tuesday from the remnants of the Pacific Tropical Storm Amanda that had caused deadly flooding and landslides in Central America. At least 22 deaths in El Salvador and Guatemala were blamed on the storm.

Cristobal was the earliest third named storm of an Atlantic hurricane season on record. In 2016, Tropical Storm Colin formed in the Gulf on June 5.