SAN FRANCISCO (KGO) -- Tropical Storm Hilary has officially moved into Southern California, bringing heavy rain to many areas and raising concerns about severe flooding and potentially destructive winds across the region.
Hilary roared along Mexico's Baja California peninsula Sunday and, as expected, was downgraded to a tropical storm with wind speeds at 70mph. By 11 a.m., Hilary made landfall as a tropical storm over the northern part of the Baja California Peninsula in Mexico.
As Tropical Hilary headed to the region, a 5.1 earthquake struck the area Sunday afternoon, according to the USGS.
It was upgraded from a 5.0. The quake occurred just after 2:40 p.m. near Ojai on the Sisar fault in Ventura County, the USGS said.
Hilary is no longer a hurricane, but it is still carrying so much rain that forecasters said "catastrophic and life-threatening" flooding is likely across a broad region of the southwestern U.S.
The Mexican cities of Ensenada and Tijuana remained directly in the tropical storm's path, and meteorologists warned that despite weakening, the storm remained treacherous.
There will be a threat of flooding rains across Southern California from Sunday through Tuesday. The U.S. National Hurricane Center issued a tropical storm watch on Friday, the first time that has ever been done.
Hurricane Hilary has been downgraded to a tropical storm hurricane from a Category 1 Sunday morning as evacuations in at-risk areas continue to be issued, according to the Associated Press.
Tropical storm warnings are in effect for more than 42 million Americans in Southern California, as Hilary is expected to be the first storm of its kind to hit the region since Nora in 1997.
Rain started to reach the southern regions of California and Arizona later Saturday and continues into Monday.
Flood watches and warnings are in effect from Southern California and Arizona to Oregon and Idaho.
FLASH FLOOD WARNING FOR LA AREA
The National Weather Service issued a Flash Flood Warning including Los Angeles, until 7:45 p.m. PDT.
A Flash Flood Warning was just issued for parts of Los Angeles, including Downtown Los Angeles, Long Beach, Glendale and parts of Ventura County through the evening hours.
California Governor Gavin Newsom declared a state of emergency for much of Southern California on Saturday ahead of Hurricane Hilary making landfall, ABC News reported.
"California has thousands of people on the ground working hand-in-hand with federal and local personnel to support communities in Hurricane Hilary's path with resources, equipment and expertise," the governor said in a statement.
There are currently "more than 7,500 boots on the ground deployed" to help local communities the governor's statement continued.
The impacts of the storm are expected to begin Saturday evening lasting through Monday, according to the statement.
VIDEO: Officials give update on CA's Hurricane Hilary response, preparedness efforts
Officials as far north as Los Angeles scrambled to get the homeless off the streets, set up shelters and prepare for evacuations.
More than 7,500 people-- from first-responders to support staff-- are ready to go.
That includes hundreds of California National Guardsmen and women.
Cal Fire is on standby as well with hundreds of engines in position.
It will have teams ready for any potential swift water rescues and prepared to search urban areas.
If you're traveling, United Airlines issued an alert saying flights could be affected Sunday until Monday.
Major League Baseball games in Southern California -- have been postponed.
The rain could produce flooding and slides particularly in areas with burn scars.
On Saturday, Hurricane Hilary "has sped up a bit, along with a slight shift eastward in its track," as it gained speed, moving toward Baja California, according to the National Weather Service Saturday morning. "This results in Sunday morning through Sunday evening being the time frame of most impact, along with slightly weaker winds."
It is then expected to continue northward up the peninsula, raising fears that its heavy rains could cause dangerous flooding in the border city of Tijuana, where many homes in the city of 1.9 million cling precariously to steep hillsides.
Hilary will rapidly weaken as it enters cooler ocean waters and interacts with the mountain terrain of Baja California Sunday.
The current track has Hilary moving into Southern California late Sunday into Monday as a tropical storm. Life-threatening and potentially catastrophic flooding is possible. For the first time ever, Tropical Storm Warnings have gone up for Southern California.
No tropical storm has made landfall in Southern California since Sept. 25, 1939, according to the National Weather Service.
Hurricanes require ocean temperatures above 80 degrees to survive. Hilary is currently sitting in 85-degree water and will remain in those warm waters through Saturday. As Hilary moves closer to Baja California, ocean temperatures will quickly cool into the 70s and eventually the 60s along the California coast.
That temperature drop may not seem like a lot but ocean temperatures in the 70s will essentially kill Hilary and water in the 60s will never support a tropical system. Thus, we see a very rapid weakening as the system approaches the California-Mexico border.
HEAVY RAIN THREAT IN SOCAL
The moisture from Hilary will bring the possibility of excessive flooding in Southern California.
The National Weather Service issued a flood watch that will be in effect starting at 11am tomorrow through Monday evening across San Diego and Los Angeles counties. Rainfall amounts of 3 to 6 inches, with isolated amounts of 10 inches, are expected across portions of southern California and southern Nevada, which would lead to significant and rare impacts. Elsewhere across portions of the Western United States, rainfall totals of 1 to 3 inches are expected.
Rough surf and strong winds will also impact Southern California.
CENTRAL VALLEY IMPACTS
Rainfall is expected in parts of the Central Valley Sunday night into Monday morning.
Most parts of the Central Valley experienced a precursor to Hilary's arrival when rain and thunderstorms arrived Saturday night, knocking out power and trees throughout cities like Fresno and Clovis.
High winds are something to consider as wind speeds are expected to be over 20 mph throughout the Valley.
Central Valley residents coming from and heading to Southern California should expect rough driving conditions through the Grapevine at I-5.
The Grapevine is expected to have 2-4 inches of rainfall and winds up to 20-30 mph, with gusts up to 45 mph.
BAY AREA IMPACTS
The current track of Hilary keeps the bulk of the moisture in Southern California and the Sierra but, we still have a possibility of seeing isolated showers here Sunday and a chance of showers Monday. Remnants of Hilary will bring higher humidity and tropical cloud cover between Sunday and early next week.
We will monitor the track of this storm and any small shifts would mean an increased chance of rain here. That is something we will fine-tune in the coming days.
ABC News and the Associated Press contributed to this report.
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