Hurricane Hilary has prompted historic weather alerts in California as millions across the Southwest begin to see initial impacts from the storm.
The worst effects are expected to impact the region over the next 48 hours, as the cyclone unleashes catastrophic, life-threatening flooding.
On Saturday, the hurricane weakened to Category 2 cyclone and that trend is expected to continue with landfall on the Mexican coast within the next 24 hours, according to the National Hurricane Center (NHC).
California Gov. Gavin Newsom declared a State of Emergency for Southern California ahead of the storm's worst impacts.
More than 42 million people are under the first-ever Tropical Storm Warning that has been issued in Southern California. It covers areas along the coast from Los Angeles to the U.S.-Mexico border, including San Diego. It also extends inland to places such as Victorville, San Bernardino, Palm Springs and Mount Laguna.
Parts of the Southwest were already being impacted Saturday by moisture from Hurricane Hilary, resulting in the issuance of Flash Flood Warnings and the closure of some roadways.
Heavy rain has already caused problems Saturday. The California Department of Transportation closed Highway 98 in Ocotillo, near San Diego, due to flooding and debris on the road.
In Palm Springs, California, firefighters say they distributed 20,000 more sandbags to residents as preparations continue. Authorities said residents living along the flood channel there have been repeatedly cautioned about the imminent risk to their lives by police helicopters circling every 90 minutes Friday.
In anticipation of the heavy rainfall, the San Bernardino County Sheriff's Office issued evacuation notices for residents in Oak Glen, Forest Falls, Mountain Home Village, Angelus Oaks, and NE Yucaipa.
These areas are known to flood during heavy rainfall events and have been the recipients of debris flows and of mudslides.
Additionally, the Los Angeles County Sheriff's Office has asked residents and visitors to leave Catalina Island ahead of rough seas and high winds.
Some sandbag locations ran low on supplies in San Diego, but CAL FIRE pledged to keep preparation efforts going as long as possible.
The Air Force Reserve "Hurricane Hunters," assigned to the 403rd Wing at Keesler Air Force Base in Mississippi, departed Saturday morning to fly weather reconnaissance missions into Hurricane Hilary to collect weather data that improves NHC's forecasts.
"By flying into the storm, crews are able to locate the low-pressure center of the storm and collect data that assists with movement and intensity forecasts," said Lt. Col. Steve Burton, 53rd WRS mission commander for the weather deployment. "The data we collect can improve a forecast by anywhere from 15-25%."
The unit will continue to fly missions into the storm throughout the weekend and possibly into Monday, said Burton.
"A lot of folks who will be impacted by the storm may not have a lot of experience with tropical cyclones," FEMA Deputy Assistant Administrator Colt Hagmaier told FOX Weather.
Most deaths from hurricanes and tropical storms occur due to inland flooding, especially when people drive through flooded streets.
"So it's really important that people have a plan of how to get out if they need to, that they listen to their local officials, and they don't drive through standing water," Hagmaier said.
The State of California says it has pre-positioned swift water rescue teams and vehicles to respond where flooding could be the worst.
