Tropical Storm Rachel is forecasted to hit northern Baja California or San Diego County by Saturday night. The storm is poised to create significant threats, especially coastal flooding. The National Hurricane Center has cautioned that Rachel might strengthen before reaching the West Coast. This is atypical for tropical storms in the eastern Pacific.
Usually, these storms weaken in cooler waters. However, El Niño conditions and a marine heat wave have elevated ocean temperatures 10 to 13 degrees above average. This warmer environment is ideal for Rachel’s growth. UC Agriculture and Natural Resources climate scientist Daniel Swain noted the uniqueness of this event during a briefing on Friday.
Potential Flooding Areas
On Friday, the National Weather Service in San Diego issued a rare tropical storm watch for most parts of San Diego County. This includes cities like San Diego, Chula Vista, Carlsbad, and Oceanside. It’s the second tropical storm watch for California ever issued.
The region faces significant coastal flooding risks, especially on south-facing shores, due to high tides and the storm’s approach. Swells may cause water intrusion and dangerous surf conditions between 3 to 6 feet, along with rip currents.
Laguna Beach residents experienced flooded streets and sidewalks on Friday. Weather officials had anticipated tides in Southern California being 1 to 1.5 feet above normal because of El Niño conditions.
By 9 a.m. Friday, tides were 17 inches higher in San Diego and La Jolla, while Santa Monica and San Francisco saw tides 16 and 14 inches higher, respectively. According to meteorologist Miguel Miller, several factors are coinciding to exacerbate flooding risks, including high tides and large surf.
A coastal flood advisory is in place for Ventura, Los Angeles, Orange, and San Diego counties until Tuesday afternoon. This advisory warns of flooding in beach parking lots, boardwalks, and roads with isolated road closures likely.
Rainfall Expectations
The remnants of Rachel are expected to bring light rain to Southern California from Sunday morning through Monday night. However, more significant rain is possible in the Mojave Desert, the Inland Empire, and parts of San Diego County.
The weather service indicates a moderate 40% chance of heavy rainfall causing flash flooding in areas like San Diego, El Cajon, Chula Vista, and Palm Springs. There are reduced chances in places like Oceanside, San Clemente, and Riverside.
In Los Angeles County, rain will likely be light to moderate, between a quarter of an inch and an inch. Heavier rain is expected in Orange County and coastal San Diego County.
Uncommon Tropical Storm Events
Historically, only two tropical storms have maintained this strength while traversing California. The first, known as El Cordonazo, struck Long Beach in September 1939. It delivered significant rain and winds, resulting in substantial damage and loss of life.
The second, Nora, in September 1997, briefly crossed the California-Arizona border as a tropical storm. Severe damage was confined to areas outside California.
Nora coincided with a strong El Niño season, which often correlates with increased hurricane activity in the eastern Pacific and above-average Southern California rainfall in winter. The 1997-98 and 1982-83 El Niños were wet periods, with downtown Los Angeles receiving significant rainfall.
This season’s El Niño is predicted to be exceptionally strong, with NOAA’s Climate Prediction Center highlighting a strong probability of record conditions. Yet, impactful weather events consistent with El Niño are not assured despite the increased likelihood.
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