With Hurricane Hilary strengthening to Category 4 status in the Pacific Ocean off the coast of Baja California as it makes its way toward Southern California, a first-of-its-kind tropical storm watch was issued Friday – then upgraded – across San Diego County.
The watch, which indicates that “tropical storm-force winds are possible somewhere within this area within the next 48 hours,” is the first ever issued in Southern California, according to the National Weather Service.
By 9 p.m., forecasters had upgraded the storm watch to a Tropical Storm Warning.
A tropical storm has not made landfall in California since 1939, forecasters said.
The warning covers essentially the entire county, including coastal areas, deserts, mountains and valleys. The difference between a watch and a warning, according to the NWS, is that a warning “is issued when sustained winds of 39 to 73 mph or higher” are expected in 36 hours or less.
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The NWS noted that the hurricane will weaken as it moves north, devolving to a tropical storm as it reaches Southern California over the weekend, but it will still pack a punch, with “life-threatening and potentially catastrophic flooding” in some desert, mountain and foothill areas, along with powerful winds Sunday into Monday.
Forecasters warned that the storm could have a number of major impacts, including:
- Flooding that might prompt evacuation orders
- Heavy rain that could turn small streams, creeks, canals, arroyos, and ditches into “dangerous rivers,” leading to potentially destructive runoff in mountain valleys that could raise the risk of rock slides, mudslides and debris flows
- Flooding of streets and parking lots that will make driving conditions dangerous and potentially prompt road and bridge closures
Moisture from the storm is expected to start impacting the region as early as Saturday.
“Widespread heavy rainfall is expected for Saturday into Monday with the most widespread and heaviest rainfall expected for Sunday night,” according to the National Weather Service.
The exact path of the storm remained in flux Friday, with forecasters noting that even slight shifts in its track could dramatically impact rainfall totals.
“Regardless of the exact track and intensity of Hilary, which could continue to change in the coming days, it will bring a substantial surge in moisture into Southern California, with heavy rainfall and a high potential for flash flooding, especially for the mountains and deserts,” according to the National Weather Service.
Forecasters said mountains in Riverside and San Diego counties could see 4 to 8 inches of rain, possibly up to 10 inches on some eastern slopes, between Saturday and Monday. Lower desert areas could receive 5 to 7 inches. Coastal areas are anticipated to get between and inch and an inch-and-a-half of rain, with valleys getting 1.5 to 2 inches.
The NWS issued a flood watch that will be in effect from Saturday morning through Monday in the San Diego County mountains, deserts, valleys and coastal areas, along with the Riverside County mountains and valleys, the Coachella Valley and San Gorgonio Pass near Banning.
Forecasters said the heavy rains could result in excessive runoff that might flood rivers, creeks and streams and cause debris flows in recent burn areas.
“In addition to the rainfall and flooding threat, another concern is the potential for strong east winds Sunday and Monday,” according to the NWS. “The wind threat will be more dependent on the track of Hilary. Should Hilary have a more westerly track, the wind threat would likely be greater, and if the track is more easterly, the threat would be less.
“The combination of heavy rainfall, the potential for flash flooding, and strong winds could very well make this a high-impact event for Southern California.”
The city of San Diego was preparing for Hilary by placing “no parking” signs in low-lying or flood-risk areas, especially crossings around the San Diego River. Stormwater Department crews will also be cleaning storm drains and inlets with a history of debris buildup, street sweeping to reduce trash and pollutants from entering waterways, and monitoring 15 pump stations and more than 46,000 storm drains citywide for any issues.
Sandbags are also available in limited supply and can be picked up at 10 recreation centers centrally located in each City Council District. Residents with identification showing proof of residency can receive up to 10 empty sandbags.
Go to the city’s storm preparedness web page for a list of the locations and other information about how to avoid flooding and storm damage.
City News Service and Reuters contributed to this article.
Updated at 11 a.m. and 9:10 p.m. Aug.18, 2023
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