Coastal communities across the United States are facing an accelerating increase in high-tide flooding, a phenomenon often referred to as "nuisance" or "sunny-day" flooding. This growing concern was highlighted by Samuel Hammond on social media, who queried, > "Seems like a pretty big deviation, but is it catastrophic or like an extra high tide?" His observation points to a significant shift in tidal patterns now impacting daily life.
The frequency of high-tide flooding has more than doubled across the U.S. since the year 2000, according to data from the National Oceanic and Atmospheric Administration (NOAA). In some U.S. coastal cities, annual occurrences have surged five to ten-fold since the 1960s. This escalation is primarily attributed to long-term sea-level rise, which reduces the buffer between average sea levels and land elevation.
Further exacerbating this trend is the influence of the 18.6-year lunar nodal cycle. While a major tide-amplifying phase is projected for the mid-2030s, the current period around 2025 marks a crucial transition. Experts note that the lunar cycle's suppressing effect on tides is reaching its minimum this year, meaning its amplifying influence will begin to accelerate flood hazard increases in the coming decade.
NOAA projections indicate a substantial rise in future flood days. By 2030, the national median frequency rate for high-tide flooding is expected to increase two to three times, reaching seven to 15 days annually. Looking further ahead, by 2050, the average number of high-tide flood days per year is likely to range between 45 and 85 across the nation.
These increasingly frequent events, which can occur without severe weather, lead to significant disruptions. They cause road closures, overwhelm stormwater systems, and impact local economies and tourism. Coastal cities are already implementing costly infrastructure projects, such as pump stations, to mitigate the effects of these persistent inundations.