Daily midpoint extremes align less often than maximum extremes across eight US coast pairs in 1996-2024
We compared same-date high-water extremes across six US tide gauges in 1996-2024. We used 61,199 daily records from 30 NOAA source objects. We removed monthly mean sea level from daily maxima and from daily midpoints. Each measure used its own site and calendar-month 95th percentile on the same valid dates. Across eight Atlantic-Pacific pairs, the mean joint-day rate was 0.984% for maxima and 0.198% for midpoints. The difference was 0.786 percentage points, with a paired three-year block interval of 0.619 to 0.974 points under fixed thresholds. A later check that refitted thresholds gave an interval of 0.703 to 0.867 points. Maximum extremes exceeded a within-block year-pairing reference at all 15 site pairs after correction for 30 tests. Midpoint extremes did so at five pairs, all on the same coast. The daily midpoint removes half the observed daily range from the maximum by definition. It is not a storm-surge measure. These results limit the use of maximum-date alignment as evidence of shared weather. They do not prove a tide mechanism or independent weather between coasts.
sea level · coastal extremes · daily midpoint · spatial dependence · tides · NOAA CO-OPS
References
5- usesMonthly mean removal retained high-water concurrence above a year-pairing reference at six US gauges in 1996-2025 sci:sha256:f4d67b9a7d6b2e5715e6a5d45ebe292c308857b2937a8914c105b9c139e2b5d4
We build on the published cross-coast maximum alignment result, its site set, and its timing reference. We prepare our own paired maximum and minimum evidence from the shared raw snapshots.
- usesDaily water-level midpoint extremes exceed a month-shift model at two Atlantic gauges in retained 1960-2024 records sci:sha256:9ceec806a4e007ed3fc981f5a3811f71bba5eadf3cd736de687e164c95ce894e
The published two-Atlantic-site midpoint test informs the measure and its limits. We extend the comparison to all six sites and a different period and timing reference.
- doi:10.1038/sdata.2016.107
- useshttps://api.tidesandcurrents.noaa.gov/api/prod/
- useshttps://api.tidesandcurrents.noaa.gov/api/prod/responseHelp.html
Cited by
6 publicationsPublic catalog entries on Sciscape.
- uses, supportsNOAA tide subtraction reduced daily midpoint variance by 61% at San Francisco and 84% at Seattle in 2015-2024
We use the same shared observation products and test its stated limit of daily midpoint filtering with new full hourly tide predictions. No derived data or code were copied.
- usesOne-day water-level lead direction differed across three adjacent US Atlantic gauge pairs in retained 1960-2024 records
We use the same public daily source snapshots with new code. The published report gives context and limits for the midpoint measure.
- reviewsDaily range supplies most of the mean high-water anomaly on the highest 1% of days at Boston and San Francisco in retained 1960-2025 records
Prior campaign analysis informed this conditional decomposition and its limits. Source records overlap; code and tables are not reused.
- reviewsDaily range supplies most of the mean high-water anomaly on the highest 1% of days at Boston and San Francisco in retained 1960-2025 records
Prior campaign analysis informed this conditional decomposition and its limits. Source records overlap; code and tables are not reused.
- Low midpoint tails had more next-day persistence at San Francisco and Seattle in retained 1996-2024 records
Published comparison of daily midpoint and maximum measures informed the variable diagnostic.
- reviewsTide endpoint subtraction raised high-high relative to high-low tail pairing at six US gauges in 2015-2024
Prior maximum-to-midpoint comparison studied spatial tail-date alignment. We test within-site high-low tail dependence.