Tropical Storm Rosa diminished from a Pacific hurricane over the weekend, but will still bring strong winds and unsafe rip currents to southern California on Monday, the National Hurricane Center (NHC) said.
The center of the Category 1 storm was 355 miles southwest of Punta Eugenia and 550 miles south-southwest San Felipe, the NHC said in its 5 a.m. PDT update.
Rosa is on track to hit the Baja California Peninsula Monday with flooding rains.
Rain chances will rise in the Valley tonight and rain looks to consume the Valley Monday morning through Tuesday night.
Rain is expected to begin Sunday afternoon in southeastern California and Arizona, where 2-4 inches is likely to fall.
"The big concern is the moisture and how much rainfall we're going to get", said Andrew Deemer, meteorologist for the National Weather Service in Phoenix.
Forecasters warned that swells generated by Rosa will affect portions of the southwestern Mexican coast through Tuesday, causing life-threatening surf and rip current conditions.
Rosa, which is now a Category 3 storm, weakened slightly off Mexico's Pacific Coast on Friday.
The center of Rosa was expected to approach Baja California Monday, but is forecast to weaken to a tropical storm by that point.
Hurricane Rosa is shown from a National Oceanic and Atmospheric (NOAA) GOES East satelite over the eastern Pacific Ocean on September 27. In issuing the flash flood watch, officials also said to be wary of flooding in burn scars from recent wildfires.