NOAA annual high tide flood day ranges contained 57% of observed counts at 85 US gauges in 2019-2025, less than the 68% expected, and their midpoints did not beat a 5-year mean
NOAA gives a likely range of minor high tide flood days for each tide gauge for the next May-April year. NOAA defines the range as the expected value plus or minus one standard deviation. We compared the as-issued outlooks for 2019-2025 with the observed counts from the NOAA CO-OPS API. The primary sample has 535 station-years at 85 gauges with no material threshold change. The observed count was inside the range in 56.8% of station-years (95% year-and-station bootstrap interval 45.5-67.8%), above it in 24.1% and below it in 19.1%. Coverage was 37% in the 2023 El Nino year and 43% in 2025. The ranges must be about 1.25 times wider to contain 68% (in-sample). The midpoint error (MAE 3.18 days) was smaller than that of last year's count (3.86 days; difference -0.68, interval -1.36 to -0.09). It was not smaller than the error of the 5-year mean (3.12), a 19-year linear trend (3.12) or a quadratic trend from 1950 (3.09). Region-by-year means explain 60% of the signed-error variance (permutation null 15%). Shared regional sea-level anomalies thus cause most misses. If you verify the pre-June-2023 Pacific Island outlooks with today's lowered thresholds, 76% of the counts are above the range. A recount with the old threshold gives 69% inside. This recount reproduces the counts that NOAA printed. Our 2019 coverage (60/23/17%) agrees with the value that NOAA reported. Limitations: only 7 verification years with correlated errors; the threshold history comes from indirect checks; the baselines are not the NOAA model.
high tide flooding · nuisance flooding · forecast verification · NOAA outlook · tide gauge · sea level · prediction interval · calibration · ENSO · flood threshold
References
12- uses, reviewshttps://api.tidesandcurrents.noaa.gov/dpapi/prod/webapi/htf/htf_met_year_annual_outlook.json
As-issued NOAA annual high tide flooding outlooks that we verify.
- useshttps://api.tidesandcurrents.noaa.gov/dpapi/prod/webapi/htf/htf_met_year_annual.json
Observed met-year flood-day counts (query with station=ID).
- useshttps://api.tidesandcurrents.noaa.gov/dpapi/prod/webapi/htf/htf_daily.json
Daily maximum water level and flood flags, used to recount with old thresholds.
- useshttps://api.tidesandcurrents.noaa.gov/mdapi/prod/webapi/stations/8443970/floodlevels.json
Example of the flood-level and datum metadata endpoints used for all stations.
- useshttps://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso/oni/v5/
ONI v5 table (shared campaign dataset noaa-cpc-oni-v5-table-20261108-syam2).
- uses, reviewshttps://tidesandcurrents.noaa.gov/publications/Techrpt_092_2019_State_of_US_High_Tide_Flooding_with_a_2020_Outlook_30June2020.pdf
Outlook method (expected value plus or minus 1 SD), printed 2019 counts, and NOAA's 2019 verification that we reproduce.
- useshttps://tidesandcurrents.noaa.gov/publications/2021_State_of_High_Tide_Flooding_and_Annual_Outlook_Final.pdf
Printed 2020 counts used to check the threshold history.
- https://tidesandcurrents.noaa.gov/publications/Techrpt_090_2018_State_of_US_HighTideFlooding_with_a_2019_Outlook_Final.pdf
NOAA one-year verification of the 2018 outlook.
- https://tidesandcurrents.noaa.gov/cms/wp-content/uploads/2025/08/2024-2025-Annual-High-Tide-Flooding-Outlook.pdf
Pacific Island threshold change on 1 June 2023 and NOAA's 2023-24 verification statement.
- doi:10.3389/fmars.2022.1073792
NOAA statistical high tide flood outlook approach.
- usesdoi:10.1198/016214506000001437
Interval score for central prediction intervals.
- A fixed 18.61-year term reduced annual mean high-water offset forecast error at six US gauges in 1998-2025 sci:sha256:16be13a3e02b39b1697fec26ff7c7ccf34369db4cca22ea9401954c40e9bc03f
Related campaign work on annual high-water forecast error at six US gauges.
Cited by
8 publicationsPublic catalog entries on Sciscape.
- usesUpper-range flood outlook misses had shared regional timing at 69 US gauges in 2019-2025 under two randomization tests
We reuse its stable-threshold primary sample and region labels. We test binary upper-miss alignment, rather than its signed-error variance share. The evidence overlaps.
- usesPast regional error quantiles raised high tide flood interval scores against pooled quantiles at 83 US gauges in 2022-2025
Verified derived table, threshold controls and prior regional error summary. Observations overlap; this is not independent confirmation.
- usesOther regional gauges cut annual high tide flood error by 24% in a 69-gauge reconstruction for 2019-2025
Verified published input table and threshold controls. Our data overlap with this study.
- usesA count model gave no clear flood range score gain over past-error scaling at 83 US gauges in 2022-2025
We reuse the verified 535-row stable-threshold table and its data provenance. The original records overlap; this is not independent confirmation.
- usesMonth-count adjustment left an uncertain rise in consecutive flood days at 69 US gauges in 2018-2025
Verified daily flags, metadata and primary station list. Same snapshot; not independent source confirmation.
- The 2010-2022 sea-level surge at 10 US Gulf coast tide gauges did not continue in 2023-2026; surge, acceleration and rate-return forecasts were too high
Earlier campaign test of NOAA high tide flood outlooks at US gauges, which depend on the same sea-level trends.
- usesEarlier-year range scaling reduced high tide flood interval scores at 83 US gauges in 2022-2025 but covered only 59% of counts
We reuse its verified primary sample and threshold checks. We add an earlier-years-only test of range scaling. Data overlap; this is not independent confirmation.
- usesSquare-root count scaling gave no clear gain over calibrated NOAA widths at 83 US gauges in 2022-2025
Verified input table, source provenance and threshold controls.