Variable Tidal Amplitude in Hawaiʻi and the Connection to Pacific Decadal Climate Variability

Abstract

Analysis of multidecadal tide records, satellite altimetry, and high-resolution oceanic reanalysis around the Hawaiian Ridge identifies correlations between offshore and onshore mean sea level (MSL), the M₂ tide, and ocean stratification; these are linked to Pacific decadal climate variability. Empirical orthogonal function analyses reveal strongly correlated quasi-decadal variability in onshore and offshore tides and MSL, and all three factors are highly correlated with regional density stratification. This decadal variability is highly correlated with multiple Pacific climate indices, suggesting that this climate variability influences internal tides via coupled ocean-atmosphere mechanisms. The surface expression of variations in the M₂ internal tide yield correlated variability between MSL and M₂ offshore and onshore. The M₂ signals at all tide gauges have stronger relationships to MSL in the altimetry era (1992–2023) than their respective full records, and both factors show stronger connections to climate variations in recent years. The magnitudes of the climate-induced tidal variations are on the order of 10% on top of MSL variability and long-term steric sea level rise. This amplification may exacerbate the frequency of high-tide flooding (also known as “sunny-day flooding”) in harbors and other low-lying areas of Hawai'i, highlighting the need for dynamic coastal management strategies that integrate astronomical, nonastronomical, and climatic factors in sea level projections.