Mexico/US: Hurricane Rosa arrival raises flash flooding concerns Sep. 30 /update 2

Event

Hurricane Rosa is set to hit the coast of Mexico on the morning (local time) of Monday, October 1, before moving into the Southwest US. Mexico's National Meteorological Service issued a tropical storm warning for the Baja California peninsula from Punta Abreojos (Baja California Sur) to Cabo San Quintin (Baja California), with tropical storm watches extending beyond those points. As of 23:00 on Saturday, September 29, Rosa was located 915 km (568 mi) west of Cabo San Lucas and moving northeast, with sustained winds of 155 km/h (100 mph). The hurricane is expected to weaken over Sunday and arrive as a tropical storm.

After passing across Baja California, Rosa is predicted to affect northwestern Sonora before entering the Southwest US. It is expected to bring rain of 7.6-15 cm (3-6 in) and possibly up to 25.4 cm (10 in) in Mexico and between 2.5-10 cm (1-4 in) across Arizona, southeast California, Utah, and western Colorado from Monday through Wednesday, October 3. The US National Weather Service (NWS) warned of life-threatening flash flooding and debris flows across the region, as far north as Salt Lake City.

Context

Tropical cyclones and hurricanes are common in the east Pacific from May through November, though most do not make landfall. Rainfall in desert areas frequently produces flash flooding, even at large distances from storms.

Advice

Individuals in the affected areas are advised to monitor local weather reports, anticipate flooding and transportation disruptions, avoid low-lying areas, including washes, riverbeds, and canyons, and adhere to instructions issued by local authorities. Remember that flash flooding and debris flows can occur at large distances from rainfall and that walking or driving through running water can be dangerous - 15 cm (6 in) of running water is enough to knock over an adult.