The deadliest single twister North America has seen so far this year ripped through the Mexican town of Ciudad Acuña with great violence. The tornado flipped over buses, tossed cars, and damaged nearly 400 homes.

“There’s nothing standing, not walls, not roofs” in a square-mile area, city spokesman Edgar Gonzalez told the Associated Press.

At 7 a.m. on Monday, a tornado emerged from an isolated supercell just south of the Texas-Mexico border in a city with a population of about 150,000 residents. Most of the border region was hit with rain and hail, but Ciudad Acuña bore the brunt of this severe weather outbreak. The National Water Commission (Conagua) in Coahuila estimates that the tornado’s wind speed reached up to 137 mph. The tornado spawned from the same set of storms that drenched the Houston area over the weekend.

Over 100 tornadoes were reported by the NOAA Storm Prediction Center over the holiday weekend, but this one, with wind speeds similar to those in an EF-3, was by far the deadliest, killing at least 13 people according to the Associated Press. Five people remain missing.

Weather Underground’s Bob Henson describes how unusual the very strong tornado is for a location this far south. “No F5/EF5 events have ever been confirmed this far south in the U.S. or Mexico, and shows that only 10 of 555 U.S. tornadoes rated F4 or EF4 between 1950 and 2014 occurred near or south of 30°N,” Henson writes. “The strong subtropical jet streams associated with El Niño typically bring very cold upper-level air, which enhances instability, and the powerful jet-level winds help ventilate the rising air within thunderstorms.”