The rain hasn't really started yet, but San Mateo County wants residents to act as if it's on the way. On Wednesday the county put out a flood-preparedness message ahead of what federal forecasters say could be one of the strongest El Niño winters on record.

The county's advice comes down to four steps, according to the Burlingame-Hillsborough Times, which reported on the post: make a plan, build an emergency kit, pick up sandbags, and sign up for SMC Alert, the county's free emergency notification system.

Why this year is different

In its September update, NOAA's Climate Prediction Center said El Niño is strengthening, with a greater than 90% chance of a "very strong" event this fall and winter. The agency put the chance of a historic event, one stronger than any El Niño since 1950, at 75% for October through December.

That forecast is about the strength of the ocean warming in the Pacific, not a promise of floods in any one town. The Climate Prediction Center itself notes that a stronger El Niño raises the odds of typical El Niño effects but does not guarantee them. Still, strong El Niño winters have brought heavy storms to California before, which is why counties around the Bay are getting ahead of it. Sonoma County has already declared a local emergency in advance of the first storm.

Where to get sandbags

Most cities in the county run their own sandbag sites, and the county keeps a full list on its winter weather page. A few examples from that list and from city websites:

  • Burlingame: a vacant lot at 600 California Dr. at Floribunda Ave.
  • Hillsborough: the Walnut parking lot at Town Hall, 1600 Floribunda Ave.
  • City of San Mateo: self-serve stations open around the clock from Oct. 1 through April 30, at the corporation yard on Pacific Boulevard, the Beresford Park parking lot and the Anchor Road/Bay Trail lot. The limit is 10 bags per vehicle, and residents should bring a shovel and proof that they live or own property in the city. People who can't fill bags themselves can call the city to arrange pre-filled bags.
  • Unincorporated areas: the county offers up to 15 pre-made bags per household each winter, plus loose sand and empty bags available 24/7, at yards in Redwood City, Half Moon Bay, La Honda and Pescadero. Pre-made bags at the Redwood City yard require a reservation and ID.

Low-lying areas

The Burlingame-Hillsborough Times pointed to Burlingame's Bayfront area, which sits low between Highway 101 and the Bay. A 2022 description from OneShoreline, the county's flood and sea level rise agency, said the existing rock floodwalls there offer only minimal protection.

SMC Alert sends texts, calls and emails about floods, fires, storms and evacuations. It's opt-in, so residents have to register, and the county suggests adding both home and work addresses so alerts match where you actually are.