What Should You Do Before and After El Niño Flooding?

Weather sources reviewed October 16, 2026

For San Diego homeowners, preparing for El Niño means thinking about both the water outside the home and the moisture that could remain inside it. Heavy rain can overwhelm drainage. Higher ocean levels can make coastal flooding worse. Once water enters a building, the work continues after the storm passes.

NOAA’s October 8 assessment found a strengthening El Niño, with strong to very strong conditions likely to continue through January–March 2027. Its October 15 winter outlook favors wetter conditions across the southern United States, including Southern California. Local flood impacts depend on the storms that develop and the conditions at each property. NOAA ENSO assessment; NOAA winter outlook.

Prepare before water arrives, act safely if it enters, and verify that affected materials are dry before rebuilding.

What does a Kelvin wave have to do with flooding?

El Niño is a coupled ocean and atmosphere pattern in the tropical Pacific. During its development, weakened trade winds and bursts of winds from the west can send pulses of warmer water eastward along the equator. When these Kelvin waves reach the Americas, part of their energy travels north along the coastline as coastally trapped waves. NOAA describes this as one way conditions in the tropical Pacific influence the West Coast. NOAA’s ocean indicators explainer.

Kelvin waves produce broad, slow changes in the ocean. Several can develop over an El Niño season, temporarily raising coastal water levels as they pass. NOAA’s Kelvin wave overview.

In an October 6 explanation, NOAA reported one Kelvin wave traveling up the North American West Coast, with one or two more behind it in the tropics. NOAA says coastal Kelvin waves can add roughly 6–12 inches to sea level. The size and timing of that temporary increase vary along the coast. Higher water levels can increase flooding when they coincide with high tides or storm surge. NOAA Fisheries, October 6.

Recent Newport Beach flooding coincided with Tropical Storm Rachel and a Kelvin wave. Los Angeles Times, October 15.

How do El Niño impacts differ along the West Coast?

El Niño affects the coast through changes in ocean water levels and atmospheric circulation. Coastal Kelvin waves can carry higher water levels north toward Canada. Meanwhile, shifts in the jet stream influence where storms deliver rain. These processes create different concerns from San Diego to Seattle. NOAA’s coastal wave explanation; NOAA’s guide to El Niño weather impacts.

San Diego, Orange County, and Los Angeles

During El Niño, the Pacific storm track often shifts south toward California. Strong events can favor a storm track into Southern California, increasing the likelihood of a wet winter. NOAA’s current outlook favors wetter conditions in this region for December 2026 through February 2027. NOAA on the storm-track shift; 2026–27 winter outlook.

For homeowners, that means preparing for intense rainfall and runoff throughout the region, with additional high-water concerns along the shoreline. Check rainfall and flood alerts for your property’s location, and coastal advisories when you live near the water.

Central and Northern California

The rainfall relationship becomes less consistent farther north. The National Weather Service reports little correlation between Northern California precipitation and most El Niño patterns. Winter conditions there depend heavily on which storms reach the region. NWS explanation for Northern California.

Across the Central Coast, Bay Area, and North Coast, pay close attention to atmospheric rivers: long, narrow corridors of water vapor that can produce heavy rain when they reach land. A strong event that stalls over a vulnerable watershed can cause severe flooding. Watch local forecasts for rainfall intensity, duration, and river conditions. NOAA’s atmospheric river guide.

Coastal Oregon and Washington

The southward storm-track shift often leaves the Pacific Northwest drier than average during El Niño winters. For the coming winter, NOAA also favors warmer temperatures in the region. These are seasonal tendencies; individual storms can still bring damaging rain and flooding. NOAA’s historical El Niño patterns; current winter outlook; West Coast atmospheric river impacts.

Ocean-facing communities should monitor coastal-flood and high-surf advisories alongside rainfall forecasts. Prepare low-lying coastal properties for periods when elevated ocean levels overlap with high tides and storm surge.

Seattle and Puget Sound

Seattle’s waterfront lies on Puget Sound, where tides, local winds, atmospheric pressure, and ocean conditions combine to influence water levels. Washington’s Department of Ecology documented more high tides than predicted in Seattle during several past El Niño winters, including 1982–83, 1997–98, and 2009–10. Washington Ecology’s historical tide analysis.

For waterfront properties, follow local tidal-flood advisories and observed water levels. For properties away from the shoreline, focus on rainfall, drainage, and water entering the building. A property-specific assessment is useful wherever recurring leaks or musty odors are a concern; our Seattle team can help you decide whether an inspection is appropriate.

What should you do before the next storm?

Use the time before rain to address known problems and make a response plan:

• Check drainage and roof condition. Clear accessible gutters and drains, remove debris that could obstruct runoff, and arrange repairs for known leaks. Our exterior maintenance guide covers roofs, flashing, gutters, and other places where water can enter.

• Review your property’s exposure. Check local hazard maps and plan safe routes out. Get sandbags before a storm if appropriate, and follow local placement guidance.

• Make sure alerts can reach you. Register with Alert San Diego, prepare an emergency kit, and agree on a household communication plan.

• Assign someone to check the property. For an unoccupied home or rental, arrange a check after storms when access is safe, with clear instructions for reporting water intrusion.

The County’s El Niño guidance and the City’s storm preparedness page provide local preparation resources. Sandbags can redirect water and can also leak, so use them as one part of your flood plan. County flood preparedness.

What should you do if water gets inside?

1. Make safety the first decision

Follow evacuation instructions and stay out of floodwater. Before entering a damaged home, have its safety assessed. Never step into standing water to reach an electrical panel; call an electrician if power cannot be shut off from a dry location. Keep portable generators outdoors and at least 20 feet from buildings, away from doors and windows. County flood safety; CDC reentry guidance.

Children should not participate in disaster cleanup. People with asthma, other lung conditions, or weakened immune systems should avoid buildings with indoor water leaks, visible mold, or a moldy odor. CDC guidance on mold after severe weather.

2. Document damage and begin a safe drying response

Once access is safe, photograph affected rooms and belongings before cleanup and contact your insurer. Record when water entered and which areas were wet. Those details also help restoration professionals understand the event. FEMA’s flood damage documentation guidance explains what to capture.

EPA recommends drying wet areas and materials within 24–48 hours to help prevent mold growth. Start as soon as access is safe. Prompt drying reduces the time moisture is available for mold growth. EPA’s mold and moisture guide.

If a flooded home and its contents have not dried within that window, EPA advises assuming mold growth is present. Drying equipment must be used safely: do not use fans where mold is already growing, and do not operate flood-affected HVAC equipment until a professional says it is safe. EPA’s flooded-home guidance.

3. Account for contamination and unsalvageable materials

Floodwater can carry sewage and other contaminants. Contaminated materials require appropriate cleaning or disposal. CDC advises discarding drywall and insulation contaminated by floodwater or sewage, along with belongings that cannot be properly cleaned and dried. Anyone who can safely participate in cleanup needs appropriate protective equipment, including gloves, goggles, and an N95 respirator or greater protection. CDC disaster cleanup guidance.

Bring in professionals experienced with contaminated-water damage. Before cutting into older walls or removing finishes, account for possible asbestos or lead hazards. Do not paint over mold or seal wet materials into a repaired wall. EPA mold cleanup guidance; EPA flood cleanup guidance.

When can a mold inspection help?

An inspection can be useful when water reached concealed spaces, musty odors persist, staining returns, or you are unsure how far the damage extends. A meaningful investigation considers the water history, visible conditions, moisture readings, and sampling when it can answer a specific question.

Begin urgent water removal and necessary cleanup as soon as it is safe. EPA generally considers sampling unnecessary where visible mold already establishes a cleanup need. Sampling results require interpretation in the context of the building; federal airborne mold limits have not been established. EPA guidance on mold sampling.

After remediation, an independent assessment can help determine whether the work met the project’s cleanup criteria. Our guide to what homeowners should do after mold remediation explains that process and the follow-up needed to keep moisture under control.