NOAA publishes how many days each US coastal gauge floods, but not how long the water stays up. This measures the hours, at 137 gauges across every usable year on record — and finds that floods come far more often than they used to while lasting about as long as they always have.
Each line is one station: the left end is how often it flooded in its first ten years of record, the right end is its most recent ten. Click any line for that station's full history.
Some gauges flood often and briefly; others rarely and for hours. Circle size is hours above the flood threshold per year, colour is hours per flood day. Last 10 usable years — click any gauge for its full record.
Flood days and flood hours tell different stories
Rays are lines of constant hours per flood. A gauge sitting above a ray floods for longer each time than one below it, however often it floods.
Every mark is a gauge. Nothing here is interpolated between them: a tide gauge measures one point on a shoreline, and the coast in between was not measured.
Recent 10-year averages, sorted by hours per flood day. years is usable years; * marks records too short for a trend claim.
Why this exists. Across these 137 gauges a flood day means anything from just over an hour above the threshold to most of a day — and NOAA's published counts score every one of them the same. NOAA's Inundation Analysis Tool can compute duration, one station and a limited date range at a time. What has not existed is the bulk history: duration made comparable across thousands of station-years alongside the published day counts. That is what this is.
The pattern behind the headline. Flood days rose at 73 of the 86 gauges with long enough records to compare their first and last decade. Over the same spans the length of an individual flood barely moved — a median change of about +0.01 hours per decade across the 41 longest records, with 28 of those 41 flat to within a quarter of their starting value. More floods, the same shape.