Tropical Storm Rachel is expected to make landfall in either northern Baja California or San Diego County as early as Saturday evening, bringing with it a host of potential hazards, including devastating coastal flooding.
The National Hurricane Center warned that Rachel, which was circling hundreds of miles off the coast of San Diego, could regain strength before arriving on the West Coast – an unusual occurrence for storms in the eastern tropical Pacific.
Typically, storms weaken significantly once they enter these colder waters. But El Niño conditions and an ongoing marine heatwave have pushed ocean temperatures 10 to 13 degrees above normal, providing a much more favorable environment for Rachel.
“Of note, this is an unusual event made possible by both the coincidence of the early arrival of this trough of low pressure off the coast of California and the record warm ocean temperatures — and I mean record heat — off the coast of California right now,” Daniel Swain, UC Agriculture and Natural Resources climatologist, said in a briefing Friday.
Where are flooding most likely?
The National Weather Service office in San Diego issued a rare tropical storm watch Friday for most of San Diego County, including San Diego, Chula Vista, Carlsbad and Oceanside, meaning tropical storm-force winds are possible over the next 48 hours. This is only the second time a tropical storm watch has been issued in California.
Coastal flooding will remain the region’s biggest concern in the coming days, particularly for south-facing coasts, given the combination of high tides, higher than usual water levels and the arrival of a tropical storm. The swells will bring not only the potential for water intrusion, but also dangerous waves — ranging from 3 to 6 feet in some areas — and rip currents, according to the weather service.
Laguna Beach residents woke up Friday morning to flooded streets and sidewalks in the city’s downtown area Friday.
(Allen J. Schaben / Los Angeles Times)
Officials had predicted that tides in Southern California would be 1 foot to 1.5 feet above normal, which is what would normally be expected without the abnormally warm ocean temperatures caused by El Niño.
Around 9 a.m. Friday, high tide in San Diego and La Jolla was 17 inches higher than the official forecast, which does not account for warmer-than-normal ocean waters or swells caused by tropical storms, according to NOAA tide forecasts. As of Friday morning, tides were coming in 16 inches higher than the official forecast in Santa Monica and 14 inches higher in San Francisco.
“We have high water already and we’re going to have periods of high tides every morning and evening, and on top of that we have high waves,” said Miguel Miller, a meteorologist with the National Weather Service in San Diego. “We have all these things piling on top of each other and we’ve already seen in recent weeks how high tides, even without big waves, put water in places it doesn’t usually go.”
A coastal flood advisory for Ventura, Los Angeles, Orange and San Diego counties – warning of the potential for flooding of parking lots, parkways and beach roads, with isolated road closures expected, as well as minor coastal erosion – is expected to remain in effect until Tuesday afternoon.
Coastal cities, including Laguna Beach, Newport Beach and Long Beach, have already experienced significant flooding. Long Beach has issued a mandatory evacuation order for residents of Seaside Walk between 64th and 66th Places.
How much rain is expected?
While tropical moisture from Rachel’s remnants is expected to bring only light rain to much of Southern California between Sunday morning and Monday evening, the Mojave Desert, Inland Empire and parts of San Diego County could see heavier precipitation.
Young Yu, of Fullerton, is reflected in the high tide that flooded Laguna Beach Friday.
(Allen J. Schaben / Los Angeles Times)
The weather service warns that there is a moderate chance, or 40 percent, of excessive precipitation that could lead to flash flooding in places like San Diego, El Cajon, Chula Vista, Escondido, Palm Springs and Twentynine Palms. A moderate risk means that many flash floods are likely and many rivers could overflow. The San Diego River near Fashion Valley may reach minor flood stage.
There is also a 15% chance of this happening in Oceanside, San Clemente, Laguna Niguel, Riverside, San Bernardino, Las Vegas, and the California-Arizona border; and 5% chance in places like Huntington Beach, Santa Ana, Long Beach, Anaheim, Pomona, Victorville, Barstow and most of Arizona and southern Utah.
In Los Angeles County, rain is expected to be light to moderate, ranging from about a quarter of an inch to an inch across much of the region. Some more rain is expected in the San Gabriel Mountains, according to the Oxnard Weather Bureau. Rain rates will likely be a quarter of an inch per hour or less, making debris flows and landslides unlikely.
A bit more rain is expected in Orange County, with coastal areas receiving between a half-inch and an inch over the weekend and early next week. Coastal sections of San Diego County could see between an inch and an inch and a half of precipitation, with higher rain levels expected further inland.
How common are tropical storms in SoCal?
In modern records, only two storms have passed through the state with tropical storm strength.
The first – nicknamed El Cordonazo, or the Whip of St. Francis – struck Long Beach and San Pedro in September 1939. It dumped 5.62 inches of rain on Los Angeles in three days, spawned wind gusts of up to 65 mph and resulted in 45 flooding deaths, with an additional 48 deaths at sea.
A wave caused by high tide and high waves generated by Tropical Storm Rachel crashes into the oceanfront home of Chris and Amy Rogers on Beach Road in the Capistrano Bay District community of Capistrano Beach.
(Allen J. Schaben / Los Angeles Times)
There was also Nora in September 1997, which briefly reached tropical storm strength as its center passed along the California-Arizona border, but California was spared the kind of damage it did to Baja California. Street flooding was reported in Imperial County, the Coachella Valley and San Diego, while large waves pushed by Nora and another storm sent breakers crashing into oceanfront properties in Seal Beach, severely damaging three homes and causing minor damage to 45 others.
Nora arrived during a “very strong” El Niño season. This trend is linked to above-average cyclone activity in the eastern Pacific, as well as above-average precipitation in southern California during winter.
This climate pattern causes warming of ocean waters in the central and eastern equatorial Pacific, leading to changes in the atmosphere that can affect weather patterns around the world.
The National Oceanic and Atmospheric Administration’s Climate Prediction Center said Thursday that there is almost a 100 percent chance that this season’s El Niño will be classified as “very strong.” There is also an 83% chance that this El Niño will be the strongest on record, dating back to 1950, compared to a 75% chance predicted last month.
“With an event of this magnitude, the chances of experiencing impacts consistent with El Niño are greater, although not guaranteed,” the Climate Prediction Center said Thursday.
There have only been four “very strong” El Niños in modern history: 1982-83, 1991-92, 1997-98 and 2015-16. Two of them – in 1982-83 and 1997-98 – flooded downtown Los Angeles with more than 30 inches of rain, more than double the region’s average annual precipitation.
The “very strong” El Niño of 2015-2016 was dry in Southern California, with downtown Los Angeles receiving only half of its annual precipitation. But it coincided with record coastal erosion along many California beaches, according to the state Coastal Commission.
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