Variable tidal amplitude in Hawaiʻi and the connection to Pacific
decadal climate variability
Abstract
Analysis of multi-decadal tide records, satellite altimetry, and
high-resolution oceanic reanalysis around the Hawaiian Ridge identifies
correlations between offshore and onshore mean sea level (MSL), M2 tidal
amplitudes, 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 M2 signal at Hilo is most
clearly connected to climate variability over its full record, stronger
even than the MSL-climate connections at all tide gauges. The amplitudes
of the climate-induced tidal variations are on 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, non-astronomical, and climatic factors, in
sea level projections.