Tropical Storm Rachel is poised to strike northern Baja California or San Diego County as early as Saturday night. The National Hurricane Center has highlighted potential dangers, notably coastal flooding. Rachel, rotating offshore from San Diego, might gain strength before reaching the West Coast, which is unusual for the tropical eastern Pacific. Normally, storms lose power in these cooler waters. However, El Niño and a marine heat wave have increased ocean temperatures by 10 to 13 degrees above normal, fueling Rachel’s intensity.
Unprecedented Conditions
Climate expert Daniel Swain from UC Agriculture and Natural Resources noted on Friday that this rare event results from an early low-pressure trough off California’s coast and exceptionally warm ocean temperatures. The San Diego National Weather Service office issued a rare tropical storm watch for most of San Diego County, including cities like Chula Vista, Carlsbad, and Oceanside. This marks only the second such alert in California.
Flooding Risks
Coastal flooding is the main concern, especially for south-facing shores. The combination of high tides, higher water levels, and the incoming storm could lead to severe water intrusion and dangerous surf, with waves reaching 3 to 6 feet in some locations. On Friday, Laguna Beach faced street and sidewalk flooding. Southern California tides are expected to be 1 to 1.5 feet above average due to El Niño’s unusually warm waters.
By 9 a.m. on Friday, San Diego and La Jolla experienced tides 17 inches above forecasted levels. Similarly, tides were 16 inches higher in Santa Monica and 14 inches higher in San Francisco.
“We’ve got water that’s already high and then we’re going to have periods of high tides each morning and evening, and then on top of that, we have high surf,” said Miguel Miller, a meteorologist with the National Weather Service in San Diego.
A coastal flood advisory is in place for Ventura, Los Angeles, Orange, and San Diego counties. It warns of possible flooding in beach parking lots, boardwalks, and roads, potentially causing closures and minor coastal erosion. Cities such as Laguna Beach, Newport Beach, and Long Beach have already seen significant flooding.
Rainfall Expectations
Rachel’s remnants are expected to bring light rain to much of Southern California from Sunday morning to Monday night. However, areas like the Mojave Desert, the Inland Empire, and parts of San Diego County might see heavier rainfall. The weather service warns of a moderate, 40% chance of excessive rainfall leading to flash floods in places like San Diego, Palm Springs, and Twentynine Palms. There is a chance the San Diego River near Fashion Valley could reach minor flood levels.
Additionally, a 15% flash flooding chance exists in Oceanside, San Clemente, and Riverside. A 5% chance applies to cities like Huntington Beach and Santa Ana. Rainfall in Los Angeles County will range from a quarter of an inch to an inch, with slightly higher amounts in the San Gabriel Mountains. Orange County might see between a half-inch and an inch over the weekend, with San Diego County’s coastal areas expecting 1 to 1.5 inches.
Tropical Storm Rarity
In recent history, only two tropical storms have hit California. El Cordonazo, or the Lash of St. Francis, struck Long Beach and San Pedro in September 1939, causing significant devastation with 5.62 inches of rain over three days and 45 fatalities due to flooding. Nora in September 1997 briefly maintained tropical storm strength near the California-Arizona border, resulting in flooding in areas like Imperial County and the Coachella Valley.
El Niño Impact
Nora arrived during a strong El Niño season, linked to increased hurricane activity in the eastern Pacific and often associated with higher-than-average Southern California rainfall in winter. El Niño involves warming of central and eastern equatorial Pacific waters, causing global atmospheric changes. The National Oceanic and Atmospheric Administration predicts almost a 100% chance of a very strong El Niño this season, with an 83% chance of it being the strongest on record since 1950.
The impacts of these strong El Niños can vary. While the 1982-83 and 1997-98 events brought significant rain to Los Angeles—over 30 inches—the 2015-16 El Niño resulted in only half the typical annual rainfall. It coincided with record coastal erosion along California beaches, emphasizing the varying consequences these weather patterns can have.