San Diego County was bracing Thursday for what is expected to be a significant surge of monsoonal and tropical moisture with widespread heavy rainfall thanks to Hurricane Hilary, which was gaining strength as it moves north off the coast of Baja California and could still pack a wallop when it reaches Southern California.
The brunt of the storm is anticipated in the county Sunday into Monday, with a high potential for flash flooding in the mountains and deserts.
Hurricane Hilary could be the first to hit San Diego in more than 100 years. The last time that happened was in 1858.
It is nearly as rare for a named storm to hit the county, according to Alex Tardy a National Weather Service Meteorologist in San Diego, who said that has only happened a few times.
“1976 Kathleen. 1977 Doreen. 1997 Nora.” Tardy said. “So, there’s not many that we can look back at historically that even have a forecast coming right at us.”
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A Pacific storm off the coast of California and a heat wave in the Midwest are creating an alley for Hilary to move straight toward San Diego.
Hitting land and colder ocean water would weaken the storm, but the system is widely expected to bring strong winds and drench San Diego.
“And we’re not used to rain in August,” Tardy said. “We usually have almost no rain in August. And we haven’t seen much rain overall for weeks, if not months.”
The exact path of the storm remained in flux Thursday, 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 received 5 to 7 inches. Coastal areas are currently anticipated to get between an 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.
NWS officials said flood watches could be issued as early as Thursday in anticipation of the heavy rains.
"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."
San Diego Gas & Electric (SDG&E) is bracing for the storm’s arrival.
Utility crews are preparing in case the wind and rain bring down power lines or cause power outages.
“We’re not only just making sure that we’re staffed up and that our crews have the resources they need,” said Alex Welling, a communications manager at SDG&E. “Making sure that they have all their vehicles, their tools, any necessary equipment that they might need to make repairs. But, they’re also on alert.”
Welling says efforts to make the grid more resilient in the face of a rising wildfire threat will help during storms.
Because high winds from Santa Ana conditions can drive wildfires, SDG&E says it has invested more than $3 billion to make the power system more resilient.
The utility has replaced wooden power poles with steel, put some lines underground and added thicker insulation to wires.
Hilary is unlikely to still be packing hurricane strength by the time it reaches Southern California, but it could still be classified as a tropical storm. The NWS noted that the only time a tropical storm made landfall in California in the 20th Century was in September of 1939.
There is about a 15% to 20% chance of tropical storm force winds over the coastal waters Sunday night through Monday, not counting possible strong winds from thunderstorms, forecasters said.
A south-southeast swell produced by Hilary has some potential to bring high surf to south facing beaches Sunday and Monday. There will also be a chance of lightning late Saturday through Monday.
