It only took half an hour. High tide floodwaters transformed stretches of dry asphalt along Marin County’s Shoreline Highway just north of San Francisco into two-foot-deep tide pools this Tuesday—coastal hazards that the National Weather Service warns will persist across the Bay Area this month into Halloween.

In a genuinely haunting preview of the havoc that warm expanding water from El Niño’s Kelvin waves is predicted to wreak during the weeks of America’s Thanksgiving and Christmas holidays, Northern California is now coping with tidal flooding from San Pablo Bay down to Monterey. San Francisco’s NPR station KQED and other local news affiliates have published drone footage of paddleboarders and kayakers navigating commuter roads beneath Highway 101 in Sausalito, but the scope of the problem has been less cute elsewhere.…