L.A. County Closes Beaches Over Lightning as Hurricane Marie Drives 7-Foot Surf

Q: Why are distant Pacific storms suddenly creating invisible sneaker wave dangers that force emergency beach closures across Southern California?

Distant Pacific hurricanes can create beach dangers in Southern California because they send long-period swells far ahead of the storm itself, even when the storm’s center stays hundreds of miles offshore. That swell carries concentrated wave energy across the Pacific and arrives at the coast in uneven sets. The result is not just bigger surf but “sneaker waves” — sudden waves that run much farther up the beach than the smaller waves before them. Forecasters warn they can appear after 10 to 20 minutes of relatively modest surf, which is why the danger can seem invisible until a large surge suddenly knocks people down or pulls them into the water. In Marie’s case, the storm’s outer influence generated 6- to 10-foot surf across parts of Southern California, with reports of 10-foot waves at Zuma Beach and even larger sets at exposed beaches such as The Wedge. That wave energy also strengthens rip currents and longshore currents, making rescues more likely even for people standing in shallow water or near rocks, jetties and piers. Emergency closures happen when those swells combine with local coastal geography and high astronomical tides. Elevated tides mean the ocean is already starting from a higher baseline, so wave run-up reaches parking lots, roads and other low-lying areas more easily. That is why cities such as Seal Beach closed beachfront lots and why weather officials extended beach hazard statements through multiple days, even as the storm itself weakened offshore.

3 articles · Updated · Los Angeles Times · Sep 6

L.A. County lifeguards closed and cleared beaches around 12:40 p.m. Sunday as lightning moved from Santa Monica to Malibu, while Malibu separately shut its beaches for public safety.
Remnants of Hurricane Marie pushed tropical moisture into Southern California, bringing heavy rain, thunderstorms and flood advisories across Los Angeles and nearby counties through Sunday evening.
7-foot swells and strong rip currents are expected to persist through late Tuesday, with Long Beach closing its boardwalk and officials warning higher tides and unsafe shoreline conditions will continue for 24 to 48 hours.
All L.A. County beaches are under an ocean-water advisory through Sept. 9 because storm runoff could raise bacteria levels, even as forecasters say the rainfall is largely beneficial and a midweek heat spike follows.