El Niño and Sea Level Rise Could Bring Double Flooding

Federal scientists are warning that the impending arrival of El Niño, combined with decades of sea level rise, could produce a “double whammy” of high tide flooding along both the West and East Coasts of the United States beginning as early as summer 2026. The NOAA Ocean Service projects that communities from California to Maine may face more frequent, deeper, and more widespread flooding — even on sunny days without storms.

The Forecast

NOAA’s Climate Prediction Center issued an ENSO Diagnostic Discussion on May 14, 2026, stating there is an 82% chance El Niño will emerge by July 2026 and a 96% chance it persists through the Northern Hemisphere winter of 2026–27. According to the Climate Prediction Center, the equatorial Pacific is showing strong signals of a developing El Niño, with subsurface temperatures increasing for the sixth consecutive month.

The ‘Double Whammy’ Mechanism

The threat stems from two converging factors. First, sea levels along U.S. coastlines have risen dramatically over recent decades — NOAA reports that high-tide flooding has increased between 300% and 925% since the 1960s. In Boston, for example, sea levels have risen nearly a foot over the last century and continue to climb at roughly an eighth of an inch per year. This long-term trend has brought tidal waters “close to the brim” in many coastal communities.

Second, El Niño — the warm phase of the El Niño-Southern Oscillation (ENSO) cycle — causes trade winds to weaken across the tropical Pacific, triggering Kelvin waves that raise sea levels along the west coast of the Americas. The warmer waters also shift the Pacific jet stream southward, altering weather patterns globally.

“It usually ends up being a double whammy,” said William Sweet, Ph.D., a NOAA oceanographer and high tide flooding expert, as reported by CBS News. “The first punch is decades of sea level rise, which has waters close to the brim in many coastal communities. And now with this second punch — a strong El Niño — coastal communities face more frequent, deeper and widespread high tide flooding along both the West and East Coasts.”

Regional Impacts

The effects are expected to vary by region. Along the West Coast, elevated sea levels and higher high tides could push strong surf much further inland than normal. On the Atlantic Coast, the shifted jet stream may steer more storms toward the mid-Atlantic, increasing storm surge events. The Gulf and Southeast Coasts are likely to see higher-than-normal rainfall.

NOAA notes that the strong El Niños of 2015–2016 and 2023–2024 both resulted in significant upticks in high tide flooding compared with non-El Niño years. The 2015–2016 event generated the greatest observed high-tide anomalies on record in the Pacific Northwest, where coastal estuaries experienced exacerbated extreme flooding.

Uncertainty in Strength

While the emergence of El Niño is considered highly likely, there remains substantial uncertainty about its peak intensity. No strength categorization currently exceeds a 37% probability, according to the Climate Prediction Center. Stronger El Niño events do not automatically guarantee stronger impacts everywhere — regional effects depend on complex ocean-atmosphere coupling patterns. NOAA will provide updated guidance in its next ENSO Diagnostic Discussion, scheduled for June 11, 2026.

Preparing for Flooding

To help communities prepare, NOAA offers several tools. The Coastal Inundation Dashboard provides real-time and forecast water level information. The agency’s Monthly Outlooks show daily flood likelihoods up to a year in advance, while the Annual Outlook provides longer-term projections.

Broader Significance

The “double whammy” warning underscores a critical reality of climate change: long-term sea level rise is making natural climate variability more dangerous. As baseline water levels continue to rise, even moderate El Niño events could produce flooding impacts that were historically associated only with the strongest events. The EcoMagazine report notes that NOAA scientists have been studying high tide flooding patterns for years and have observed an uptick in flooding even when compared to previous strong El Niños of 1982–1983 and 1997–1998.

What to Watch For

Coastal communities from California to Maine should prepare for more frequent high tide flooding events starting as early as summer 2026 and continuing through the winter of 2026–27. The flooding can occur without storms — simply from higher-than-normal tides riding on elevated sea levels. Infrastructure impacts may include road closures, increased strain on stormwater and wastewater systems, and property damage. The next key update from NOAA’s Climate Prediction Center is expected on June 11, 2026, which may provide greater clarity on the strength and timing of the developing El Niño.