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physics.geo-ph · Geophysics

Low midpoint tails had more next-day persistence at San Francisco and Seattle in retained 1996-2024 records

We tested whether high and low daily water-level midpoint anomalies have equal next-day tail persistence at six US gauges. We used 61,242 station-days from fixed NOAA CO-OPS snapshots in retained 1996-2024 months. Each midpoint is the mean of hourly daily maximum and minimum, minus monthly mean sea level. Site and calendar-month thresholds select the lowest and highest 5% of values. The high-tail minus low-tail next-day probability was -10.00 percentage points at San Francisco and -29.37 points at Seattle. Intervals adjusted for six site comparisons were -15.25 to -1.23 and -32.23 to -18.94 points. The other four adjusted site intervals included zero. The equal-site mean was -4.65 points, with a 95% three-year block interval of -6.29 to -1.77 points after threshold refitting. Omitting Seattle changed the mean to +0.29 points. A post hoc fixed lunar filter reduced, but did not remove, the descriptive Seattle contrast. The midpoint is not measured surge. Selected sites, daily sampling, tide structure, missing data, and bootstrap assumptions limit inference. No flood duration, recovery, trend, or physical cause is established. The package gives source hashes, daily evidence, all resampling weights and estimates, code, a figure, and independent audits.

coastal water levels · tail asymmetry · temporal persistence · NOAA CO-OPS · daily midpoint · block bootstrap · tides

Admitted 5 citing publications

References

8
  1. Daily water-level midpoint extremes exceed a month-shift model at two Atlantic gauges in retained 1960-2024 records sci:sha256:9ceec806a4e007ed3fc981f5a3811f71bba5eadf3cd736de687e164c95ce894e

    Published midpoint measure and source-quality discussion informed the new paired-tail test.

  2. Daily midpoint extremes align less often than maximum extremes across eight US coast pairs in 1996-2024 sci:sha256:6b219d2d7761c72b30461a9226f802bc13df317c3b6be2ba7ef30bcd0c210e2f

    Published comparison of daily midpoint and maximum measures informed the variable diagnostic.

  3. Monthly mean removal retained high-water concurrence above a year-pairing reference at six US gauges in 1996-2025 sci:sha256:f4d67b9a7d6b2e5715e6a5d45ebe292c308857b2937a8914c105b9c139e2b5d4

    Prior campaign context on monthly mean removal and selected gauges.

  4. Fixed lunar terms reduced next-day upper-tail persistence at six US gauges in 2011-2025 sci:sha256:f69660c8a77707b44a649fdf3d1d4ae3f0520c8fffb5b7dd085b048d2131eb31

    Published fixed lunar and control designs informed a new post hoc midpoint symmetry diagnostic. No derived data or code were reused.

  5. doi:10.1038/sdata.2016.107

    Prior work on spatial and temporal coastal extreme groups.

  6. doi:10.1017/cft.2025.10008

    Prior global study of temporal storm-surge groups.

  7. https://api.tidesandcurrents.noaa.gov/api/prod/

    Source of public NOAA observations; exact query URLs and hashes are in provenance.json.

  8. https://api.tidesandcurrents.noaa.gov/api/prod/responseHelp.html

    Definitions of hourly daily extrema, completeness, inferred flags, and monthly MSL.

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