UPDATE 4-Arlene to drench large parts of central Mexico
* Arlene expected to drench much of central Mexico
* Storm path over Tamaulipas, oil refineries
* Storm could approach hurricane strength at landfall (Recasts, updates with details of news conference)
MEXICO CITY, June 29 (Reuters) - Large parts of central Mexico face torrential rains once Arlene, the first tropical storm of the Atlantic hurricane season, makes landfall early on Thursday.
Mexican emergency services recommended communities in the storm's direct path evacuate and state oil monopoly Pemex [PEMEX.UL] was on alert for possible impact to refineries and other facilities in the storm's path.
Still, the storm -- likely to strengthen toward hurricane strength overnight -- will probably not hit major offshore oil fields directly, according to forecasts from the U.S. National Hurricane Center.
Mexican authorities said the storm was expected to be 435 miles (700 km) wide and drench parts of central Mexico with up to 60 inches (150 cm) of rain by Saturday, affecting areas as far away as the Pacific coast.
Arlene, moving west, had maximum sustained winds of 50 mph (85 kph) and was located about 95 miles (155 km) east of the fishing town of Tuxpan in Veracruz state on Wednesday afternoon, the NHC said, adding that it was likely to approach hurricane strength at landfall.
Landfall is expected near Tuxpan early on Thursday and local emergency services said about 200,000 people were exposed to the storm's worst impact.
"Everyone in an area which is at risk is urged to seek safe ground," Laura Gurza, a rescue official with the Interior Ministry, told a news conference.
Mexico's government extended its Gulf Coast hurricane watch from La Cruz southward to the beach area Barra de Nautla in Veracruz, which is about 200 miles (320 km) south of Tampico, where Pemex has its 190,000-barrel-per-day Madero refinery.