Flood Preparedness

Prepare Now for Coastal Flooding and Potential Wet Weather

A strong El Niño raises the odds of a wetter winter. OneShoreline encourages readiness across San Mateo County by taking steps today so that residents are prepared well ahead of any winter weather.

San Mateo County Emergency Management leads storm preparedness across the county. Refer to County winter weather page for the latest updates and preparedness information.
Sign up for SMC Alert Find sandbags

A Strong El Niño Raises the Odds of a Wet Winter and Extreme Weather

El Niño is a recurring warming of the tropical Pacific Ocean that shifts storm tracks and influences weather over several months. This year's El Niño is on track to be one of the strongest on record, and forecasters expect it to continue to strengthen through the end of the year.

NOAA's winter outlook favors wetter-than-average conditions from California across the southern U.S. Fall rain has little to do with El Niño, so late October and into November may feel ordinary but preparedness is still important. Climate scientists put the chance of a wetter-than-average winter statewide above 90%, with high confidence for the Bay Area, and the chance of a dry winter at 5 to 10% or lower. The wettest weather is most likely in January and February, and El Niño’s effects should be strongest from December through March.

Coastal flooding is the clearest risk. Water levels along much of the California coast are already running 1 to 2 feet above predicted tides, breaking records for the highest October tides since 1983. This winter’s highest high tide windows are Nov 24–26, Dec 22–25 and Jan 20–23, but coastal and bayshore tidal flooding will likely be regularly occurring.

Getting ready now costs little and pays off either way.

Forecast information updated 10/26/2026. Sources: NOAA Climate Prediction Center, NOAA CPC, Prognostic Discussion, Weather West.

Four Steps to Take Now

Getting prepared now costs little and pays off either way. Take these four steps before the first storm.

  1. Know your flood risk

    Find out whether your home sits in a flood zone. Follow the steps under Find the Flood Zone for Your Property to look up your address or parcel number on the County's map. If your home is at risk, get flood insurance. Learn how at FloodSmart.

  2. Sign up for SMC Alert

    Get warnings for your address by text, phone call and email at smcalert.info. Moved? Update your address. If you get Nixle messages, sign up for SMC Alert too; the two systems are separate.

  3. Make a household plan

    Agree on where your household will meet, choose an out-of-area contact, and know two ways out of your neighborhood. Look up your evacuation zone at Genasys Protect.

  4. Build a stay kit and a go kit

    Your stay kit holds what you need at home for at least 3 days if roads close or the power goes out: water, food, medications, flashlights and chargers. Your go kit is a bag you can grab if you need to leave, with medications, chargers and copies of important documents. Use the Ready.gov supply kit checklist (PDF).

Find Sandbags Near You

Pick Up Sandbags Early

  1. Find a site. Use the map below.
  2. Place them right. Put them at doors, garage entries and low vents.
  3. Help a neighbor. Offer to carry or fill bags for someone who can't.

Once you've taken those 4 steps, find your sandbag site before the first storm. Many sites limit how many bags you can take, and some serve residents only.

Start with your city or town's site. County sites serve unincorporated areas. Hours, limits and supplies can change during storms, so check with the site before you go. See the full list of sandbag sites (PDF).

  • Bring gloves and a shovel, and work in pairs.
  • Fill bags 1/2 to 2/3 full so they lie flat.
  • Filled bags weigh 30 to 50 pounds, and more when wet. Ask for help lifting.

When a Storm Is Coming

Storm Coming? Do 3 Things Now

  1. Charge phones, power banks and flashlights.
  2. Clear gutters and the storm drain by your home.
  3. Secure furniture, bins and loose items by bringing them inside.

Watch National Weather Service forecasts, SMC Alert, city and County updates, and road conditions on Caltrans QuickMap.

Act:

  • Gather your supplies.
  • Move vehicles and belongings out of low areas.
  • Stay away from flooded roads, trails, underpasses and the shoreline.
  • Report flooding or a clogged storm drain to your city's public works department.
  • Follow instructions from emergency officials.
Don't drive or walk into floodwater. 6 inches of moving water can knock you off your feet, and 12 inches can carry away most cars. Never drive around barricades; find another route or wait it out. If floodwater traps you indoors, move to a higher floor or the roof, not the attic, and call 911.

Protect Your Home

Check Your Flood Coverage

Homeowners and renters can both prepare. Most home and renters policies don't cover flooding, and renters can insure their belongings too.

  1. Call your agent. Ask exactly what your policy covers.
  2. Act this month. New flood policies usually take 30 days to start.

Homeowners and Renters

Get your home ready and choose flood protection supplies on Flood Readiness: Simple Steps for Your Home. Download the Household and Renter Flood Checklist (PDF).

Check on Each Other

The Fastest Warning Is Often a Neighbor

  1. Trade numbers with at least 1 neighbor.
  2. Agree to check in. Call or knock when an alert goes out.
  3. Know who needs help, such as neighbors who live alone or have limited mobility.
In an emergency, or if anyone's life is in danger, call 911.

Sandbag supplies, site hours, road conditions and other details can change quickly during storms. Always confirm with the responsible agency. This page shares general preparedness information and doesn't replace instructions from emergency officials. To read this page in another language, use the translate button at the top of the page. Automatic translation may contain errors.