The blistering heat that has baked Southern California for days is coming to an end, with rain on tap for the weekend and early next week, along with a risk of potentially damaging coastal flooding.
Tropical Storm Rachel, which has been moving northwest across the Pacific Ocean, is expected to make a sharp right turn toward Baja California on Friday. That, paired with two unrelated low-pressure systems moving in from the north, will result in several hours of moderate rain between Saturday night and Tuesday, according to the National Weather Service.
Timing
The highest chances of rain are between Sunday morning and Monday night, forecasters say. Rain rates are probably going to be a quarter of an inch per hour or less, making debris flow and landslides unlikely. Rainfall totals are expected to range from a quarter of an inch to three-quarters of an inch.
The rain is also expected to coincide with significantly cooler temperatures, said Ryan Kittell, a meteorologist with the National Weather Service office in Oxnard.
“We do see relief coming,” Kittell said. “We’ll see that cooling trend continue and really kick into gear Friday and Saturday, such that by Sunday and Monday we’ll actually see highs generally in the 70s, which is a far cry from what we’ve seen for most of this week.”
Flooding risk
Coastal flooding will remain the biggest concern for the region in the coming days, particularly for south-facing shores including Long Beach, Malibu and Point Mugu.
Tides in Southern California are expected to be 1 foot to 1.5 feet above what would ordinarily be expected without the abnormally warm ocean temperatures wrought by El Niño. The high tides, low-pressure systems, strong waves and wind ranging from 20 to 40 mph all could contribute to flooding along the coast.
A coastal flood advisory for Ventura, Los Angeles, Orange and San Diego counties — warning of the potential for flooding in beach parking lots, boardwalks and roads, with isolated road closures expected, along with minor coastal erosion — is expected to remain in effect through Tuesday afternoon.
It’s too soon to say just how severe the impacts will be, forecasters say. But if the strong winds, tides and low-pressure system overlap on Sunday, “a more significant coastal flooding event will be likely,” the weather service said in its forecast.
Coastal warnings
Large waves have already hammered the Long Beach Peninsula this week, sending water onto the boardwalk and streets. Video showed waves on Thursday slamming against the bulkhead that protects beachfront homes.
Officials in the city began handing out sandbags to residents on Thursday, warning people living in historically vulnerable areas like the Peninsula and around Alamitos Bay to prepare immediately for the risk of flooding. The city has already been besieged by an unusually active, El Niño-fueled hurricane season, taking damage from Hurricane Marie over Labor Day weekend and Hurricane Polo last month.
High tide and a swell that rolled in early Thursday washed away part of the access road leading to San Onofre State Beach on the border of Orange and San Diego counties. The beach has suffered significant coastal erosion in recent years and advocates say it could be hit hard this winter.
While San Onofre remains open, pedestrian and bicycle access will be partly restricted Friday while crews work to address the damage. The lower dirt parking lots of Surf Beach are closed to vehicles indefinitely, according to a state parks spokesperson.
Forecasters also expect strong rip currents and dangerous waves in the coming days, which increase the risk of drowning for people swimming at the beach.
Inland could be hit harder
While tropical moisture from the remnants of Rachel is expected to deliver only light rain to much of Southern California, the Mojave Desert and the Inland Empire could see more significant showers.
Forecasters said there’s a 15% chance of excessive rainfall Sunday that could lead to flash flooding in wide swaths of the Mojave, as well as in Palm Springs, Las Vegas, Zion National Park in Utah, and much of Arizona, including the Grand Canyon. By contrast, there’s only a 5% chance of that in Los Angeles County, Orange County and the Inland Empire.
This comes as forecasters say odds are increasing that this El Niño will be the strongest in the modern record, which goes back 76 years.
El Nino Update
On Thursday, the National Oceanic and Atmospheric Administration’s Climate Prediction Center said the chance of a historic, record-breaking El Niño is now 83%, up from the probability of 75% issued last month. The climate pattern typically emerges every two to seven years and is marked by the heating of ocean waters in the central and eastern equatorial Pacific, which spurs changes in the atmosphere that can affect weather around the world.
In Southern California, strong El Niños are generally associated with higher-than-average rainfall. The strongest El Niño years, which occurred in 1957-58, 1982-83 and 1997-98, left a swath of devastation across the state.
But not all turn out that way. The 2015-16 El Niño season didn’t deliver elevated rainfall, but resulted in record coastal erosion.
“From the big picture standpoint … all that warmth in the Pacific Ocean means there is a whole lot more energy available to convey to the atmosphere to create those storm systems that come along,” Michael Anderson, a state climatologist with the Department of Water Resources, said during a California Natural Resources Agency webinar on Thursday.
“There is all the energy we have ever seen available for these wintertime storms to make use of, and that’s why we want to pay attention,” he added.
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