Nambiathody, A., Rodriguez, A.R., Thompson, P.R., Merrifield, M.A., Mazloff, M.R., Menemenlis, D., and Hamlington, B. (2026)
Presented at:
Ocean Sciences Meeting 2026Low-lying Pacific Island nations face an existential threat from sea level rise, which is already impacting communities through more frequent flooding and coastline changes. The Rising Nations Initiative (RNI), supported by the UN Global Centre for Climate Mobility, aims to mobilize international support for these nations including Tuvalu, which recently announced plans to digitize its government in response to the threat of the island’s submergence. As part of a broader partnership between the NASA Sea Level Change Team and the RNI, this study examines how often high-water thresholds have been exceeded at tide gauges in RNI nations and Hawaii, and how these events relate to anomalous sea level conditions. When water levels exceed established thresholds, often during high tides, these events are referred to as High-Tide Flooding (HTF) events. For each location we quantify how often these thresholds were exceeded over the available tide gauge record and identify the proportion of these events associated with anomalous sea level conditions. Our preliminary analysis of tide gauge water levels around the Island of Hawaii shows that daily maximum water levels exceeding the flooding threshold are around 40 cm above Mean Higher High Water (MHHW), and almost all are associated with non tidal residuals of ~10 cm above MHHW lasting 20-40 days in duration, indicating these events were likely not a result of storm surge. Some events showed high residual water levels but did not exceed the flood threshold, likely due to low tide. A large fraction of HTF events occurred during high tide. Using satellite altimetry, we examine whether mesoscale Sea Surface Height (SSH) anomalies can be linked to the anomalous sea levels observed at the tide gauges. A high-resolution ocean model, which reproduces the observed sea-level variability, is employed to investigate the underlying dynamics of these mesoscale features and their coastal impacts. We further assess the statistical significance and coastal influence of the high-tide events attributable to mesoscale SSH anomalies. Our results offer new insights into the remote drivers of coastal flooding at the Pacific Island locations and underscore the importance of regional ocean dynamics in shaping sea level risk for vulnerable island communities. The insights gained will support the development of improved forecasting capabilities, which are essential for enhancing the resilience of island communities to future ocean-related hazards.
