(Adds Pemex statement, updates storms' locations, rainfall)
MEXICO CITY, Sept 2 (Reuters) - Tropical storm Dolly was expected to make landfall on Mexico's northeast coast on Tuesday night, the U.S. National Hurricane Center (NHC) said, bringing up to 15 inches (38 cm) of rain and life-threatening flash floods.
In a statement, Mexican state oil giant Pemex said it was keeping an eye on Dolly and if needed would suspend its operations in the eastern states of Veracruz and Tamaulipas, including the Francisco Madero refinery, the country's smallest.
The severe weather has already forced the closure of two of the major crude oil export terminals used by Pemex.
The 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 miles (64 km) east-southeast of Tampico in northeastern Tamaulipas state, the NHC said.
Dolly was blowing maximum sustained winds of 45 miles per hour (72 km per hour) and moving west at 10 mph, the NHC said. The storm is expected to bring up to 15 inches of rain across 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.
Mexico's national water authority Conagua said Dolly will likely cause waves of up to 4 meters (13 feet) along the country's northeastern Gulf of Mexico coastline.
However, the NHC said Dolly, which formed in the southern Gulf of Mexico early on Tuesday, was expected to weaken on hitting land.
Meanwhile, Tropical Storm Norbert formed on Tuesday off southwestern Mexico, and is about 145 miles (233 km) west of the major Pacific port of Manzanillo, the NHC said.
Norbert is churning north at 9 mph (14 kph), the NHC said, blowing maximum sustained winds of 45 mph. The NHC expected it to strengthen over the next 48 hours.
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. (Reporting by David Alire Garcia and Gabriel Stargardter in Mexico City and Debasis Mohapatra in Bangalore; Editing by Lisa Shumaker)