Low-lying stretches of Marin County went underwater Monday as high tides pushed into Mill Valley streets, closing a key commuter corridor and prompting police warnings to stay clear of the area. Coastal parts of the Bay Area remained under a flood advisory as the tidal surge continued to threaten roads, businesses and bike paths through the week.
Flooding shut down sections of multiple roads Monday in Mill Valley, according to Patch, which reported that police urged drivers to avoid the affected stretches entirely. The west side of Redwood Highway Frontage Road was closed between Hamilton Drive and the southbound U.S. Highway 101 Seminary Drive off-ramp, the outlet reported. Miller Avenue was also shut down between Camino Alto and Almonte Boulevard, per a Mill Valley Police Department alert issued at 11:39 a.m. Monday.
Both closures were expected to stay in place until the floodwaters receded, and drivers were told to follow posted detours rather than attempt to push through, the same report noted. Some low-lying areas of Marin County experienced tidal flooding Monday while coastal parts of the Bay Area sat under a flood advisory, according to kioncentralcoast.com.
How Long the High Tides Will Linger
The National Weather Service said high tides could cause minor flooding in low-lying coastal areas across the San Francisco Bay Area through Saturday, as reported by NBC Bay Area. The risk extends to bayshore locations along San Pablo Bay, San Francisco Bay and Monterey Bay, as well as low-lying stretches along the Pacific coast, the station reported.
Forecast tide heights for the San Francisco tidal gauge vary depending on the source. NBC Bay Area reported the gauge is expected to peak at 1.9 feet above normal Wednesday, reaching 7.7 feet above mean lower low water, with tides of 1.8 feet above normal Tuesday and 1.7 feet above normal Monday and Thursday. Citing the seed report from CBS News, the San Francisco tidal gauge was forecast to reach 2.1 feet above normal at 12:15 p.m. Tuesday — a figure that diverges from NBC Bay Area's numbers for the same day. High tides can also vary by up to 90 minutes earlier or later along the coast and through San Francisco Bay, per the CBS report.
Why This Keeps Happening in Marin
Flooding like Monday's is not a one-off for Marin's lowest-lying roads. The Chronicle previously reported that high tides shut down the northbound Highway 101 off-ramp in Mill Valley around 12:30 p.m. on Oct. 11, the same day a gauge at San Francisco's Crissy Field recorded a water level 1.73 feet above the average highest daily tide, setting a new October record and surpassing the prior October mark of 1.4 feet set in 2025. Back in January, a stretch of Miller Avenue between Almonte Boulevard and Camino Alto was closed in both directions during an earlier high-tide event, the Chronicle reported.
Weekend king tides in June also caused coastal flooding in Larkspur and Corte Madera, including along Lucky Drive, Redwood Highway and the Golden Hind Passage neighborhood, according to KQED. The outlet also reported that Bay Area water levels have risen nearly 2 millimeters per year on average over the past three decades, with projections showing the ocean and bay could climb about a foot by 2050 and more than 6 feet by the end of the century.
Marin County Public Works has noted that high tides can bring localized flooding to coastal areas such as Tam Junction even on sunny days, and that a significant storm could worsen impacts in spots already prone to year-round tidal flooding. Separately, the Chronicle reported that El Niño is fueling record-breaking sea surface temperatures off the California coast, with warmer water contributing to higher tides through thermal expansion.
What Comes Next
The National Weather Service has also forecast a 20% to 40% chance of rain from Friday into the weekend, with low to moderate confidence, according to NBC Bay Area's report, raising the possibility of compounding effects on already saturated low-lying areas. High tides are not unique to Marin this year — ABC7 Los Angeles reported that similar tidal flooding hit streets and businesses in Newport Beach and Long Beach in Southern California.
For now, Mill Valley drivers are being told to steer clear of the closed stretches of Miller Avenue and Redwood Highway Frontage Road until the water recedes, with posted detours in place in the meantime. Residents in low-lying parts of Marin and the wider Bay Area should expect the tidal flooding risk to persist through the week as forecasters continue tracking the advisory.
