REGION — 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 today 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. A tropical storm has not made landfall in California since 1939, forecasters said.
The watch covers essentially the entire county, including coastal areas, deserts, mountains and valleys.
The NWS noted that the hurricane will weaken as it moves north, devolving into a tropical storm as it reaches Southern California over the weekend, but it will still pack a punch, with heavy rain likely to prompt flash flooding in some mountain and foothill areas, along with powerful winds Sunday into Monday.
Forecasters warned that the storm could have 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; and
— 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.”
More storm resources for North County here.
