If it feels like your favorite harbors are flooding more often, you're not wrong. Since 2000, the frequency of so-called "sunny day" flooding along U.S. coastlines has more than doubled. By 2050, NOAA projects that some harbors could see anywhere from 45 to 85 flooding days a year. Offshore storms and storm surge, should they happen to coincide with astronomical high tides, can increase the severity and impact of high tide flooding.

NOAA's ability to keep the public informed about the potential for these high-water events has largely been through its monthly flooding outlook, which until now sorted flooding potential into three categories: unlikely, possible, or likely. US Harbors has used NOAA's flooding outlook as the basis of our popular monthly high tide flooding report, converting the federal agency's data-driven presentation into a monthly narrative that is easily understandable.

This month, NOAA has taken a leap forward by assigning more specific probabilities to its flooding forecast, giving you an additional level of detail to know if (and, if so, when) your favorite harbor is likely to flood. With the more detailed probability levels, the US Harbors team has rolled out a new flooding report presentation. We use the same color-coding and percentage chance rating system that NOAA employs, but display it as an easy-to-scan list of harbors that could be impacted, organized into regional groups. We also specify the dates when elevated water levels may be present, allowing you to preview the potential severity and anticipate a flooding event in advance of receiving a coastal flooding weather alert.

Our new flooding report can be generated using two different flooding threshold models. NOS minor uses a nationally consistent formula based on tidal range, making it the best choice for comparing flooding risk across harbors, and so we have chosen this as our default setting. NWS minor is a second option, with data calibrated by local forecasters and emergency managers to reflect where flooding actually causes problems in a specific community. While NWS minor can offer a more accurate threshold for a single harbor, be aware that it isn't available at every station.

The new flooding report is the first of several improvements that the US Harbors team has in development to expand our data and prediction offerings. As coastal inundation possibilities and impacts become more important for life on the coast, I'm excited to share new updates we are working on with you, so stay tuned. Thanks for being here with us.

— Jamie and the US Harbors Crew

Have you experienced high tide flooding in your harbor recently? Hit reply, share your story, and let us know what you think of the new report design while you're at it.

Photo credit: Shutterstock 010110010101101

September 2026 High Tide Flooding Predictions

Mean sea levels are generally higher in the late summer and early fall months, due to warmer temperatures and weather patterns, and this month higher tides can be expected around the new moon on September 10 and the full moon on September 26. Expect the elevated water levels to persist for a day or two after each. The Mid-Atlantic, Southeast, Gulf Coast, and the Big Island of Hawaii are the regions most likely to see flooding this month. For most harbors in these areas, NOAA predicts a Slight Chance (now defined as a 5-20% likelihood of flooding) when using the National Ocean Service's minor flooding threshold, measured against the Mean Higher High Water datum. Norfolk, Virginia, and the Outer Banks community of Duck, North Carolina, have a Medium Chance (up to a 40% likelihood), as will Trident Pier, Cape Canaveral, Florida; Eagle Point, Galveston Bay, Texas; and Hilo, Hawaii. Harbors on the West Coast, in contrast, are unlikely to see flooding this month.

Different thresholds will show more harbors at risk. We use the NOS minor threshold as our benchmark, as we have in previous reports, because its nationally consistent formula makes it the best basis for comparing flooding risk from one harbor to the next. The report can also be generated using the NWS minor threshold, which local forecasters and emergency managers calibrate to reflect where flooding actually causes problems in a specific community. NWS minor is not available at every station.

Make sure to print out the tide chart for your favorite harbor so that you are prepared, no matter what the coastal conditions end up delivering.

Photo credits (top to bottom): The new high tide flooding report from US Harbors; A flooded road, Photo by Shutterstock, 010110010101101; NOAA Autonomous Surface Vehicle in Narragansett Bay during testing, Photo Courtesy of Chance Maritime Technologies; CT scan of a Mariana snailfish. Image courtesy of Adam Summers/University of Washington; Satellite image of three tropical cyclones: Hurricanes Fausto and Genevieve and Typhoon Dolphin. Photo by NOAA Satellites; Atlantic bumpers, one of the fish species being raised from larvae as part of the collaboration. Image credit: NC Aquarium at Fort Fisher