Abstract
The Hawaiian Islands experienced record-high sea levels during 2017,
which caused nuisance flooding in vulnerable coastal communities and
exacerbate beach erosion, especially when positive sea level anomalies
coincided with high tides. To build toward solutions for mitigating
inundation risk, the predictability of daily-averaged sea level
anomalies is investigated. Background sea level around the Hawaiian
Islands was elevated during most of 2017 due to an oceanic Rossby-type
planetary wave, which propagated slowly westward across the tropical
North Pacific over the course of a year. The investigation focused on
leveraging observed westward propagation that sea level anomalies
exhibit over a range of timescales to make subseasonal predictions.
Daily near-real-time gridded altimetry (CMEMS/AVISO) was used to specify
upstream sea level at each site with propagation speeds based on
mode-one baroclinic Rossby wave speeds. The skill of the predictions
exceeds persistence at most locations around the archipelago out to a
month or more lead time, but the skill is highly dependent on location
even over the short distances spanned by the Hawaiian Ridge. Here,
hindcast results are presented that establish where skillful subseasonal
predictions can be made in Hawaii, as well as the barriers to
predictability in locations where they cannot. These results inform the
oceanographic and modelling communities about what processes need to be
resolved in order to provide island communities with useful short-term
sea level forecasts as the frequency of flooding events increases.