Forecasting seasonal sea level anomalies around tropical Pacific islands

At the University of Hawaii Sea Level Center, we are delivering a real-time forecasting product of monthly mean sea level anomalies that is being served online to the tropical Pacific island community. The goal is to reduce the residual between predicted tides and observed water levels by forecasting relative sea level changes for the next six months. Advancements forecasting seasonal climate variability using coupled ocean-atmosphere models, which have the ability to assimilate and predict sea level, provides the opportunity to assess the likelihood for future high or low water events several months in advance. Successfully communicating seasonal forecasts of sea level, while still in development, may support sustainable development in the tropical Pacific by helping to mitigate some of the risks of sea level rise and other climate hazards. Here, the challenges will be discussed of both producing a skillful seasonal outlook of sea level and then communicating this information to potential users. The discussion will be framed in the context of forecasting recent high and low sea level events that occurred in the tropical Pacific. For example, many Pacific islands including Hawaii and parts of Micronesia experienced recurrent high-tide flooding after the end of strong El Niño in 2016, which persisted through 2017. During the intensification of El Niño until its peak at the end of 2015, sea levels were well below-normal in much of the tropical western Pacific, offsetting the rapid regional sea level rise of the prior two decades. Such high sea levels increase coastal vulnerability to potentially damaging inundations during storms. Conversely, low sea levels expose coastlines to ecological damage and sometimes inhibit navigation.