Hilary threatens flooding disaster as torrential rain pushes north in California, Nevada
As Hilary pushes northward through Southern California and Nevada into Monday, an extraordinary amount of rain will trigger life-threatening flash flooding in some locations and dangerous travel conditions in many areas.
Hilary made landfall over the northern Baja California Peninsula around 11 a.m. PDT on Sunday as a hurricane and will continue to spread copious amounts of rain, gusty winds and severe thunderstorms in much of California and Nevada, as well as western parts of Arizona into Monday, AccuWeather meteorologists warn.
As of 2 a.m. Monday, Hillary had lost wind intensity and transitioned to a tropical rainstorm. Sustained winds were down to 35 miles per hour as it crossed into western Nevada.
Even though Hilary has transitioned to a tropical rainstorm, life-threatening conditions, including a flooding disaster, are the main concerns as the storm every so slowly unwinds, AccuWeather meteorologists say.
“The impact from Hilary is an extraordinary event -- one that is rare and unprecedented," AccuWeather Director of Forecasting Operations Dan DePodwin said.
In some of the desert areas and mountains in Southern California to southern Nevada, more than a year's worth of rain could fall.
A flash flood warning was issued for Los Angeles, Long Beach and Glendale, California, by midday Sunday.
As the rain continued to pour down in much of Southern California into Sunday evening, rainfall totals were ramping up quickly. As of 4 p.m., Mount Laguna had picked up 5.12 inches of rain with 3.96 inches drenching Ranchita. In Nevada, 5.50 inches had fallen on Bristlecone Trail.
In the deserts, Palm Springs has picked up at least 3.17 inches of rain as of the early morning hours on Monday. Close to 0.91 of rain fell in 1 hour Sunday afternoon. The city only typically picks up 0.43 of an inch of rain all summer. Palm Springs could potentially receive an entire year's worth of rain from this storm over 24-48 hours. The historical average annual rainfall for the desert town is just over 5 inches.
Downtown Los Angeles had picked up 2.43 inches of rain, which began around 7 a.m Sunday morning.
In addition to Palm Springs, torrential rainfall and flooding are likely in other desert cities and parks, including Las Vegas and Death Valley, which could turn into a massive lake. The heaviest rain and worst flooding is likely to stay west of Phoenix, but flash flooding is likely in metro areas along the Colorado River basin.
A general 2-4 inches of rain is forecast to fall with the likelihood of a foot of rain or more in the wettest mountain and desert locations in Southern California and west-central Nevada. A substantial amount of that rain will fall in less than 12 hours. An AccuWeather Local StormMax™ rainfall of 20 inches is projected.
High risk of infrastructure damage from California to Nevada related to excessive rainfall, flooding
Forecasters have rated Hilary a 2 on the AccuWeather RealImpact™ Scale for Hurricanes in the United States predominantly due to the high risk of life-threatening and potentially catastrophic flooding.
Dangers on the roads due to flooding, mudslides and washouts will continue to increase through Sunday night and into Monday morning. Small streams and dry stream beds will turn into raging rivers.
For this reason, AccuWeather meteorologists have assigned a high to extreme risk to lives and property.
Infrastructure in the area may not be able to handle the historic rainfall amounts.
"Across interior Southern California, road and rail line closures due to major flooding, washouts and mudslides are likely, putting a significant strain on infrastructure," DePodwin said.
While weather conditions may improve substantially on Monday over San Diego, Los Angeles and much of Southern California, the problems from the excessive rain are likely to linger. Some roads may remain blocked by high water or debris. It may take some time for airline and seaport operations to return to normal.
Some sections of major highways and rail systems may be damaged to the point where they could be closed for an extended period following the storm.
North of San Bernardino, California, a stretch of Interstate 15 was closed in both directions preemptively due to the expected heavy rainfall by the California Department of Transportation.
Evacuation warnings have been issued for some communities in San Bernardino County, California, in anticipation of the storm, the county's sheriff's office announced on Saturday.
Damaging winds, severe thunderstorms and isolated tornadoes may continue to be a problem from Hilary
Even though Hilary will not be a powerhouse in terms of winds for the United States, gusty winds are still likely to knock down trees, cause power outages and lead to minor property damage can occur, according to DePodwin.
Despite the storm losing a great deal of wind intensity since its passage into California, tropical storm-force gusts of 40 mph or greater can still be spread across parts of the Intermountain West.
Occasionally, tropical systems produce severe thunderstorms and tornadoes for a time after landfall. The risk of both will continue into Monday over the region.
Hilary was once a powerful Category 4 hurricane, but cool water and land interaction have knocked down winds
Hilary peaked in intensity Thursday night as a powerful Category 4 storm with maximum sustained winds of 145 mph, several hundred miles to the southwest of the southern tip of Mexico's Baja California Peninsula.
This image of Hilary was captured as the hurricane was near peak strength as a Category 4 storm several hundred miles off the coast of Mexico on Friday morning, Aug. 18, 2023. (NOAA Satellite)
"As Hilary moved over progressively cooler water this weekend, peak winds steadily declined," AccuWeather Tropical Meteorologist Alex DaSilva said.
Water temperatures off Southern California's coast are similar to those near Atlantic Canada this time of year and generally in the upper 50s to low 70s. The threshold for tropical systems to thrive is about 80 degrees Fahrenheit.
Friday morning, the National Weather Service in San Diego issued a Tropical Storm Watch for the first time in the local office's history. Friday evening, the watches had been upgraded to Tropical Storm Warnings for Catalina Island and areas along the California coastline from the Mexican border to Point Mugu.
A few days after AccuWeather sounded alerts about the coming deluge, on Friday morning, the National Weather Service issued a high risk of excessive rainfall for the low deserts to the eastern slopes of the mountains in Southern California. This is the first time on record that the NWS has issued such an advisory in the area, at least in the last 13 years. The high-risk zone includes Palm Springs and the Coachella Valley, California.
Hilary could hit California's agricultural region hard
The magnitude of flooding is likely to drop off substantially to the east and west of Hilary as it pushes inland over a narrow corridor of the western U.S. as a tropical rainstorm. However, enough rain is likely to fall to cause flooding over parts of California's San Joaquin Valley.
California is responsible for producing approximately two-thirds of the fruits and one-third of the vegetables produced in the U.S., according to the United States Department of Agriculture.
July through October are the busiest harvest months of the year, particularly in the San Joaquin Valley where most of the produce is grown.
In this Friday June 21, 2019 photo, the sun peaks past almonds growing on the branches of an almond tree at the Wenger Ranch in Modesto, Calif. (AP Photo/Rich Pedroncelli)
"A cool, wet spring has the harvest of many crops behind schedule," AccuWeather Agricultural Meteorologist Dale Mohler said. "Fresh fruits and vegetables may be susceptible to mold and spoilage due to excessive rain and further delays in the harvest from the storm. Cotton may be discolored, and yields may be reduced. Winds may knock almonds to the ground, where they may become moldy or rot due to the incoming rain."
A quick and significant rise along tributary streams and rivers of the San Joaquin is likely from Sunday to Tuesday. A significant surge of water may follow along the San Joaquin River as well.
On a potentially positive note, the delay in harvest may avoid a disaster in the raisin industry.
"All U.S. raisins are grown within a 75-mile radius of Fresno, California," Mohler said. "Growers may just halt the already delayed harvest, which is just getting underway, until after Hilary's rains have moved by."
If a substantial number of roads and rails are damaged in Southern California, shipping of crops and other products from California to parts of the U.S. could be subject to further delays.
Locally heavy rain and isolated flooding may extend as far to the north as Montana early this week, AccuWeather Long-Range Meteorologist Brandon Buckingham said. Thunderstorms that erupt on the fringe of the rain zone may spark new wildfires.
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