Could Southern California be at risk of flooding from the remnants of a hurricane this Labor Day weekend? It’s a possibility, some weather experts say, and scientists are closely watching Tropical Storm Marie develop Tuesday in the eastern Pacific Ocean, south of the Baja California peninsula. Marie is expected to turn into a hurricane by Wednesday, the National Hurricane Center said.
There’s high uncertainty over the path the storm will take, the National Weather Service office in San Diego said. But its development underscores the weather conditions that have affected Southern California this summer: unusually hot ocean temperatures and intense humidity. The threat of extreme weather is expected to intensify this winter, with a “very strong” El Niño climate pattern expected in the central and eastern tropical Pacific Ocean.
If El Niño performs as forecasted, it’ll trigger changes in the atmosphere that will move the winter storm track farther south, sending Southern California above-average rain and big waves and risking a season of erosion and flooding on the coast. The intense storm activity in the Pacific this summer may be a preview of what’s to come. The development of Marie comes amid an unusually active hurricane season in the eastern Pacific, likely related to El Niño and record-setting ocean temperatures in the tropical ocean.
Those factors, which increased moisture in the atmosphere
Those factors, which increased moisture in the atmosphere that strengthened the Southwest monsoon, helped fuel the extreme weather that resulted in last weekend’s deadly flooding in the Grand Canyon. Tropical Storm Marie’s final path remains unclear. The most likely scenario is that Marie will simply veer to the west, according to the weather service. But there’s also a chance the storm system will head north and make its way over Southern California, bringing with it the risk of flooding, said UC climate scientist Daniel Swain.
The most realistic worst-case scenario is not an actual hurricane landing in Southern California, Swain said. Even if the storm system heads to the region, said Sebastian Westerink, meteorologist for the weather service’s San Diego office, “by the time this storm reaches Southern California, it will very likely be below hurricane status and even tropical storm status.” Swain said a more likely medium-impact scenario would be “a decaying tropical storm that weakens to below-tropical-storm strength before bringing breezy conditions, tons of moisture, and some pretty hefty showers and thunderstorms into Southern California this weekend, along with waves that will be dangerous along the coast.” Regardless of Marie’s final path, meteorologists do have moderate confidence in a risk of coastal flooding for the Labor Day weekend in Southern California, according to the weather service, with swells from the storm forecasted to arrive on Saturday and Sunday, just as some of the highest high tides of the month come in.
“There’s increasing confidence in moderate-to-large surf from the south swell starting as early as Friday. We could have coastal flooding because we’ll have above-normal tides during the same time,” especially along south-facing shores, said Kristan Lund, meteorologist with the weather service office in Oxnard. People planning trips to the beach should go to one where lifeguards are on duty, the weather service said, as large waves and strong rip currents are likely.
The winds wouldn’t really be the concern
The winds wouldn’t really be the concern in any scenario; there’s no need to board up windows, Swain said. “There is essentially no scenario where the winds from this event would be stronger than what you get in a strong winter storm.” The worry, if the remnants of Marie did head to Southern California, would be the rain. Among the possible scenarios are a tropical storm that makes landfall near L.A.
Should there be heavy rainfall in the mountains, it would pose a serious threat of flash floods, landslides and debris flow Another scenario involves a storm track similar to the one in 2023 that sent a post-tropical low from the remains of Hurricane Hilary over Southern California. The National Weather Service office in Oxnard said there’s a low chance of widespread moderate-to-heavy rain with flooding
Although L.A. was spared a direct hit from Hilary, it did cause roughly $900 million in damage in the U.S. and at least $14 million in damage in Baja California Sur (there were no estimates for Baja California). There were two deaths in Baja California — two people who drowned after their vehicles were swept away by floodwaters — and a woman in California presumed dead after her mobile home was washed away in flooding along the Santa Ana River in San Bernardino County.
Among the areas hard hit in 2023
Among the areas hard hit in 2023 were the Coachella Valley, San Bernardino County and Death Valley National Park. In California’s modern record, there have been only two storms that were at tropical-storm strength as they passed through the state. One was a September 1939 storm nicknamed El Cordonazo, or the Lash of St. Francis, which hit Long Beach and San Pedro. It dumped 5.62 inches of rain on L.A.
over three days, sent wind gusts of up to 65 mph and resulted in 45 deaths from flooding on land, with an additional 48 deaths at sea. There was also Nora in September 1997, which was briefly at tropical storm strength as its center passed along the California-Arizona border, but California was spared the kind of damage it delivered to Baja California. Street flooding was reported in Imperial County, the Coachella Valley and San Diego, while big waves boosted by Nora and another storm sent breakers crashing into beachfront homes in Seal Beach, seriously damaging three homes and resulting in minor damage to 45 others.
Nora arrived during a “very strong” El Niño. That pattern is linked to above-average hurricane activity in the eastern Pacific, and also is usually tied to above-average rainfall for Southern California in the winter. Researchers suspect that a hurricane last directly impacted California on Oct. 2, 1858. It was unknown to meteorologists until about 22 years ago. Scientists went through newspaper accounts and other observations and concluded the hurricane was due west of San Diego and lashed the city with hurricane-force winds, while tropical-force storm winds were felt all the way up to the Long Beach area, according to a report in the Bulletin of the American Meteorological Society in 2004.
The storm was so powerful that ships
The storm was so powerful that ships were driven ashore, the report said, adding: “Today, if a category-1 hurricane made a direct landfall in either San Diego or Los Angeles, damage from such a storm would likely be on the order of a few to several hundred million dollars.” For a hurricane or a tropical storm to hit Southern California, Westerink said, “you almost need the perfect storm …
of a hurricane that forms somewhere out in the Pacific, is very strong and sort of barrels along the Baja coast as a Category 4 or 5, and manages to keep its momentum until it reaches Southern California without having weakened below hurricane status. “So that’s very hard, because the waters off Southern California and northern Baja are below 80 degrees, which is almost a critical threshold temperature to sustain hurricanes,” Westerink said.
Temperatures in the ocean around Southern California are higher due to a long-standing and unusual marine heat wave, but are generally in the high 60s or low 70s. “That’s a little bit warm for this time of year, no doubt,” Westerink said, “but still not warm enough to sustain a hurricane or tropical storm.” Researchers say that more attention needs to be placed on the threat of tropical cyclones — a term that includes hurricanes and tropical storms — to Southern California.
A report published in the journal Nature Climate
A report published in the journal Nature Climate Change in June warned that the kind of punishing rains brought by Hurricane Hilary might not be so exceedingly rare in a world affected by human-caused climate change. “Our results suggest a broad consensus on the increased [tropical cyclone] rainfall risk under a warmer climate,” said the report, co-written by scientists at Western Michigan University, Stanford University and MIT.
“Southern California’s population exposure to [tropical cyclone] rainfall-induced landslides will likely increase rapidly from the present to 2050, driven by both the elevated probability of extreme [tropical cyclone] rainfall under a warmer climate and projected population growth.”
