August 20, 2023 Storm Hilary batters California after making landfall in Mexico

As Southern California braced for a highly unusual summer storm Sunday afternoon, residents were struck by a much more familiar phenomenon: a magnitude 5.1 earthquake, according to the US Geological Survey.

The epicenter of the quake was in Ojai, between Santa Barbara and Ventura, and it occurred along the Sisar fault, USGS data showed.

There were no immediate reports of damage, the Ventura County Sheriff said in a social media post. County aviation units later reported no damage after flying over the Lake Casitas and Matilija dams and the city of Ojai.

Shaking was felt throughout Los Angeles and surrounding communities, according to a USGS tool that allows residents to self-report their experience.

There were no initial reports of injuries or structural damage in Los Angeles, according to the city's fire department. First responders from all 106 stations are in "earthquake mode," surveying their areas and looking for damage to power lines, transportation infrastructure, apartment buildings and large gathering sites.

About 50 miles away in Valencia, the quake felt like a slow roll, lasting about 20 seconds. Residents reported a slow-rolling effect in the Hollywood area, as well.

At least two aftershocks — measuring 3.1 and 3.6 — followed the initial quake.

Earthquake expert Dr. Lucy Jones said it appears to have been preceded by a small foreshock sequence that began Saturday morning.

USGS seismic reports are preliminary and are sometimes adjusted.

Gov. Joe Lombardo issued a state of emergency for Nevada due to Tropical Storm Hilary, according to a news release.

The declaration follows Lombardo’s decision to activate 100 National Guard members to southern Nevada earlier this week in preparation for the storm.

The Federal Emergency Management Agency has also deployed staff to the state to support its response.

CNN’s Colin Jeffery contributed to this report. 

Southwest Airlines and Frontier Airlines have suspended flights to and from Ontario International Airport, it announced online.

Southwest is suspending all flights from 12 p.m. PT Sunday through 10:30 a.m. PT Monday. Frontier has suspended all flights Sunday and Monday, the airport added. 

Officials told passengers to reach out to their airlines for updated status on their flights. 

Ontario International Airport is located in San Bernardino County, about 40 miles east of Los Angeles.

San Diego officials are bracing for the full effects of Tropical Storm Hilary to hit in the next several hours and have strategically placed resources throughout the area to quickly respond to rescues, power outages and downed trees, officials said in a Sunday news conference.

The storm is about 90 miles from the US border and about 115 miles southeast of downtown San Diego, the National Hurricane Center said at 2 p.m. local time (5 p.m. ET).

Some areas of San Diego County have already seen 3 to 4 inches of rain and are expected to see three times that much as the storm moves through, NOAA meteorologist Alex Tardy told media. The county’s desert and mountains can expect five to 10 inches of rain.

The storm “already gathered its strength, its moisture, and its rain and wind, and that’s coming our way,” Tardy said, noting that some rock slide and debris flows are already occurring.

Rural areas are expected to get hit the hardest by the storm, and first responders are coordinating across different agencies, San Diego County Sheriff Kelly Martinez said.

Gloria urged San Diego’s population of 1.3 million residents to stay at home, and said he hopes major issues that develop this evening will be handled by morning.

With Tropical Storm Hilary barreling toward the United States, over 300 flights have been canceled at Las Vegas’ Harry Reid International Airport on Sunday.

According to the tracking website FlightAware, 21% of the flights scheduled to depart from Harry Reid today have been canceled — that's a total of 165 flights.

Additionally, 23% of the flights — a total of 170 flights — that were scheduled to arrive at the airport on Sunday have also been canceled, the website notes.

Extra rescue boats and crews are stationed on Catalina Island in case there is a need to get people out, Los Angeles County Supervisor Janice Hahn told CNN Sunday.

Officials urged visitors and vulnerable residents to leave Saturday, and the last scheduled boat taking people off the island has left, Hahn said.

Officials from the sheriff’s office and rescue boat crews are now staying on the island to help if needed.

The biggest concern on Catalina, a popular vacation spot located off the coast of Southern California, is that it only has one power plant, Hahn said. If the plant flooded, it could cause a massive power outage to the entire island.

“Being on an island 26 miles from the mainland makes it a little more difficult if we really need to help them out,” she added. 

Hahn said the county is also concerned about getting the city's homeless population to higher ground. Hahn said the sheriff’s office is going tent by tent, encampment by encampment, to alert those in the area along the LA River that they should evacuate.

An evacuation order has been issued by the Mohave County Sheriff’s Office for areas of Lake Mead National Recreation Area, according to a Facebook post by the department.

The recreation area's facilities and public areas have been closed, according to the park’s website.

Lake Mead National Recreation Area is the largest national recreation area in the United States. Located in both Nevada and Arizona, the park is 1.5 million acres, the website says.

Las Vegas and surrounding areas are under a state of emergency due to Tropical Storm Hilary, as declared by Clark County Manager Kevin Schiller.

The county made the official proclamation to ensure additional resources will be available if needed, it said in a tweet.

Lake Mead National Recreation Area – just 30 miles east of the city – is closed to all recreational use, according to an alert on its official website. The lake and its surrounding wilderness are popular boating, hiking and camping destinations.

Hilary’s core is only a few hours away from crossing into California and conditions are starting to worsen.  

Flash flood warnings were issued for more than 9 million people in downtown Los Angeles and surrounding areas as heavy rain came down.

Rainfall totals in Southern California’s highest terrain have already eclipsed 2 inches, with the worst yet to come.  

Rain that has been falling since the early morning hours is only going to get heavier throughout the afternoon and evening once Hilary moves through Southern California.

Rainfall rates in Hilary’s heaviest bands could reach a staggering 2 to 4 inches per hour through Sunday evening, the National Weather Service in San Diego warned. This is enough to flood areas used to tremendous rainfall, but could be disastrous in mountainous and desert areas.  

Winds have gusted up to 78 mph in the Southern California mountains even before Hilary enters the state. The strongest winds from Hilary in the US will occur late Sunday afternoon through Sunday evening.