Warmer Nino 3.4 coincided with a wider monthly water-level range at Sewells Point in 1960-2025

We tested whether ENSO shifts monthly water levels or changes their range at six selected US tide gauges. We used 4,689 NOAA CO-OPS station-month records in 1960-2025 and the NOAA CPC ERSSTv5 Nino 3.4 anomaly. Fits removed calendar-month means and a linear time trend. At Sewells Point, the highest-minus-lowest level rose by 2.92 cm per C. The pointwise 95% three-year block interval was 1.01 to 4.83 cm per C. Six-site adjusted range limits also stayed above zero with three-, five- and ten-year blocks. At San Francisco and Seattle, mean levels rose by 3.55 and 2.78 cm per C, while range intervals included zero. The other five sites also had range intervals that included zero. Tidal-cycle terms, time splits, inferred-data removal and removal of three large ENSO events left a positive range slope at Sewells Point. These are descriptive associations. They do not prove a cause, a forecast skill, or a change in storm surge. Selected harbor sites, reused data, missing records, remaining tides, and model and block choices limit inference. The package gives fixed monthly evidence, exact source hashes, code, figures and independent numerical checks.

ENSO · sea level · monthly range · tide gauge · block bootstrap