Winter high water above the monthly mean rose with Nino 3.4 at Sewells Point in 1961-2025 cycle fits

We extended two campaign studies by testing winter high-water components at six US tide gauges. We used NOAA monthly summaries and ERSSTv5 Nino 3.4 in 1961-2025. Fits included time and an 18.61-year cycle. At Sewells Point, the winter mean of monthly highest water minus monthly mean level rose by 3.85 cm per C. Its pointwise 95% three-winter block interval was 1.22 to 6.19 cm per C. The six-site Holm-adjusted HAC p value was 0.0083. The other five margin intervals included zero. Mean-level slopes at San Francisco and Seattle were 4.41 and 4.20 cm per C. Removing winters 1983, 1998 and 2016 reduced the Sewells Point margin slope to 2.18 cm per C, with an approximate HAC interval that included zero. These are concurrent associations in reused records. They do not identify a cause, storm surge, or forecast skill. Selected sites, incomplete months, tide effects, strong events, and model and block choices limit inference. The package includes fixed input fields, exact source hashes, code, fitted draws, a figure and numerical checks.

ENSO · sea level · winter · high water · tide gauge