A satellite image of Hurricane Hilary as it churns toward Baja California.
(Via National Oceanic and Atmospheric Administration)
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Hurricane Hilary brings high risk of flooding for SoCal coast, deserts, mountains

Hurricane Hilary, gaining ferocity on its march toward Southern California, had strengthened to a Category 4 storm as of Friday morning and is expected to make landfall in Baja California on Friday night. The storm is forecast to track inland and, as of early Friday, have little impact on Santa Cruz County.

Hurricane Hilary, gaining ferocity on its march toward Southern California, is expected to bring pounding rain and a “distinct risk” of flash floods, forecasters say.

The storm, gaining strength off the southern tip of Baja California, was rated Category 4 and was expected to strengthen before reaching landfall in Mexico on Friday night. However, the cooler water will weaken the storm significantly by the time it reaches San Diego County, according to meteorologist Brandt Maxwell of the National Weather Service.

“Right now it’s looking like we’ll still have a tropical storm when it moves into Southern California, but it’s going to be weakening pretty quickly,” Maxwell said.

The storm is expected to impact Southern California starting Sunday evening through Monday, bringing rainfall amounts heretofore unheard of during the summer months. As of early Friday, it was forecast to move inland and have little impact on Santa Cruz County and the San Francisco Bay Area.

a map shows forecast impacts of Hurricane Hilary on the western United States
(Via National Weather Service)

“The most important thing will be the heavy rain, which will be widespread, and there’s a distinct risk of flash flooding,” Maxwell said of the forecast for Southern California.

A flood watch is set to take effect along the coast from Ventura to San Diego County from Sunday evening through Monday night. Inland counties such as Riverside, San Bernardino and Imperial will also have a flood watch in effect this weekend through Monday. Rainfall amounts will vary significantly, with desert cities such as Palm Springs and Yuma, Ariz., expected to receive up to 5 inches in a matter of days.

“Generally speaking, coastal areas from Los Angeles to San Diego will likely get at least 2 inches of rainfall total, with the emphasis being Sunday through Monday,” Maxwell said.

Mountain areas are expected to receive the highest amount of rainfall, particularly along east-facing slopes, as the storm approaches from the south. Maxwell estimates parts of Southern California could see 5 to 10 inches of rain.

The storm will also see heightened winds from the northeast and east, though forecasts remain uncertain as to what speeds the winds will reach.

“It won’t be consistent,” Maxwell said. “Some mountain areas will be much windier than others.”

a map shows forecast impacts of Hurricane Hilary on the western United States
(Via National Weather Service)

Maxwell emphasized that the most important thing Southern California residents could do was prepare for the potential for floods, especially those living near areas susceptible to flooding, like a canyon or floodplain.

“If you’re near a burn scar, there could be debris flow from heavy rains,” Maxwell said.

Adam Roser, a meteorologist with the National Weather Service in San Diego, said Hilary is moving into two different systems: a weak trough of low pressure off the coast of Southern California and the relentless ridge of high pressure that’s hovered over Texas and moved across the southwest U.S. this summer.

“Hilary is kind of going to squeeze through there, and it really depends where those pressure systems are going to be situated,” Roser said.

Jamie Rhome, the deputy director of the National Hurricane Center, expects more detailed forecasts for the storm’s impact on Southern California to be available Friday.

“It’s going to be a big rainmaker,” he said. “I don’t care if the peak winds are 50 mph or 30 mph. … Those rains are most likely to spread over [somewhere] in the southwestern U.S. and cause flooding problems.”

This story originally appeared in Los Angeles Times.

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