The National Weather Service (NWS) issued a flash-flood watch Friday for large parts of the south-central U.S. state of Texas that are home to more than 10 million people, due to storms expected to drop as much as 37.5 centimeters of rain in some areas through the weekend. The warning stretches from the border with Mexico north through San Antonio and into the Dallas area, a region where heavy rain and flooding in May killed more than 20 people and caused extensive damage. "Heaviest rains are expected late tonight through Saturday night, with the heavy rain threat expected to shift east on Sunday," the NWS said. Nearly 100 flights were canceled at the Dallas/Fort Worth airport, one of the country's busiest, by mid-morning Friday. Storms hit western Texas on Thursday night, causing floods about 475 kilometers northwest of Austin, the state capital, and causing numerous road accidents in the cities of Abilene and Odessa. The Texas storms are caused by a high-altitude weather pattern that is beginning to interact with Hurricane Patricia, which threatens Mexico from the Pacific Ocean, the NWS said. Patricia strengthened into a potentially catastrophic category-5 hurricane as it moved toward Manzanillo and Puerto Vallarta, having grown at an "incredible rate" in the past 12 hours, the World Meteorological Organization said Friday.