Large swathes of central Mexico were facing torrential rains as Arlene, the first tropical storm of the Atlantic hurricane season, hit the coast at sand barrier Cabo Rojo early Thursday.
Mexican officials advised communities in the storm's path to evacuate and state oil monopoly Pemex was on alert for threats to its refineries and other facilities.
However, the U.S. National Hurricane Center said Arlene would probably not become a full-fledged hurricane, and is not likely to hit major offshore oil fields directly.
Arlene hit land south of Tampico, where Pemex has its 190,000-barrel-per-day Madero refinery. Pemex said the refinery was operating as usual but it had taken the precaution of securing tankers and smaller boats at the adjoining port.
Mexico's government extended its Gulf Coast hurricane watch from La Cruz southward to the beach area Barra de Nautla in Veracruz, about 200 miles south of Tampico.
Bigger inland refineries in Salamanca, producing 245,000 bpd, and Tula, with 315,000 bpd capacity, were also in the storm's forecast path.
Mexico is a top oil exporter to the United States and almost all its exports are shipped from the Gulf of Mexico.
Mexican authorities said the storm was expected to be 435 miles wide and drench parts of central Mexico by Saturday, affecting areas as far away as the Pacific coast. Around 20 states were likely to be hit, authorities said.
Arlene, moving west, had maximum sustained winds of 65 mph and was 45 miles north of the fishing town of Tuxpan in Veracruz state on Thursday morning, the NHC said.
Strong winds and rain of 4 to 8 inches are expected to batter the eastern states of Tamaulipas, Veracruz and eastern San Luis Potosi and reach Mexico City by Friday. In mountainous areas as much as 15 inches may fall, the NHC said.
"These rains could cause life-threatening flash floods and mudslides," the center said.
Mexico's northeastern Atlantic coast is popular with local tourists for its beaches but many poor coastal towns lack flood defenses.
"Everyone in an area which is at risk is urged to seek safe ground," Interior Ministry rescue official Laura Gurza said on Wednesday.
The rains could bring some relief to farmers in the area who have been suffering from a prolonged dry spell.
Hurricane Beatriz, the second tropical storm of the Pacific season, hit Mexico last week but did no major damage.
