Tropical storm Dolly lashed Mexico's northeast coast on Tuesday night, the U.S. National Hurricane Center (NHC) said, bringing torrential rain and life threatening flash floods.

Dolly was blowing maximum sustained winds of 72 km/hour, but having made landfall the storm was expected to lose strength by Wednesday evening, NHC said.

Dolly, which formed in the southern Gulf of Mexico early on Tuesday, has already forced the closure of two of Mexico's three major crude oil export terminals.

According to national water authority Conagua it was whipping up waves of up to 4 metres along the coast.

Storm could shut oil refineries

State oil giant Pemex said in a statement that it was watching Dolly's progress and if needed it would suspend its operations in the eastern states of Veracruz and Tamaulipas, including the Francisco Madero refinery, the country's smallest.

Cayo Arcas port had been shut since Sunday afternoon while the Dos Bocas hub was closed early on Monday, the Communications and Transport Ministry said. Mexico's third major oil export terminal at Coatzacoalcos remained open.

Dolly, the fourth named storm of the 2014 Atlantic hurricane season, was about 40 kilometres south-southeast of Tampico in northeastern Tamaulipas state, the NHC said.

Dolly was moving west at 14 km/hour, the NHC said. The storm is expected to bring up to 38 centimetres of rain across areas of Tamaulipas and Nuevo Leon states.

"This rainfall is expected to cause life-threatening flash floods and mud slides in areas of mountainous terrain," the NHC said.

2nd storm forms in Pacific

Meanwhile, Tropical Storm Norbert formed on Tuesday off southwestern Mexico, and was about 515 kilometres southeast of the southern tip of the Baja California peninsula, the NHC said.

Norbert was headed further out to sea, churning north-northwest at 13 km/hour, the NHC said, blowing maximum sustained winds of 72 km/h. The NHC expected it to reach hurricane strength on Thursday.

Mexico suffered its worst floods on record last September when tropical storms Manuel and Ingrid converged from the Pacific and the Gulf of Mexico, killing more than 150 people and causing damage estimated at around $6 billion.