Tropical Storm Dolly formed off Mexico's northeastern coast on Tuesday and headed toward landfall in Tamaulipas state, threatening to spark floods and mudslides, forecasters said.

The storm packed maximum sustained winds of 85 kilometers per hour (50 miles per hour) as it churned in the Gulf of Mexico, some 140 kilometers (85 miles) southeast of the town of La Pesca, according to the US National Hurricane Center.

Dolly was moving west-northwest at 26 kilometers per hour and could strengthen before making landfall overnight, the center said.

The storm is expected to produce between 150 and 250 millimeters (six and 10 inches) of rainfall in Tamaulipas and the neighboring states of Veracruz and San Luis Potosi, according to Mexico's National Weather Service.

The service urged ships to take extreme precautions due to high waves.