Monitoring the climatology and extremes of coastal sea levels for the U.S. Coast

Coastal flooding is caused by oceanic and atmospheric processes that interact on a range of timescales to affect the local, regional, and global sea level. Major flooding during storms may be caused by large waves, high seas, and heavy rainfall. Minor flooding sometimes occurs without a storm, if the tides and sea level are higher than normal. For example, daily record high water levels in Miami, Florida were set nearly every month during 2019, which caused flooding nuisances such as road closures. Most of the high water levels occurred during fair weather,  without obvious physical explanations for elevated sea level. Recent sea-level extremes are affecting not only Miami but many low-lying regions of the U.S. Coast and Pacific Islands. With ongoing sea-level rise, and the likelihood of future increasing seasonal-to-interannual variability,  coastal sea level anomalies are likely to cause more frequent and severe flooding.  

The University of Hawaii Sea Level Center developed a web product to monitor recent and past water levels, compared to the long-term climatology and records at tide gauge stations. The visualization product seeks to inform how tide gauge observations relate to what is typical for the time of year, or to compare with extremes during past years. It was inspired by similar types of graphical displays of weather and climate extremes, such as heat waves, widely available on the web but uncommon for coastal water levels. Missing from this product is near-real-time cataloging and the ability to provide an understanding of sea-level extremes, which stakeholders desire to improve situational awareness and help inform about future occurrences.  

We will develop a monitoring product for tracking and understanding daily, monthly, and seasonal sea level extremes for the U.S. Coast. The product will describe the characteristics of sea level anomalies as they occur using tide gauges, satellite observations, and climate analyses.  A diagnostic of the physical contributions and forcing mechanisms will be included to explain why sea levels are elevated, as outreach suggested this is of interest. Our methodology will be adapted from existing diagnostic tools, which have been applied to understand the physics of past high sea-level events. We will expand and generalize established methodologies for assessing sea-level variability to be applicable nationally and in near real-time.  

Our research is relevant to the MAPP competition “New Climate Monitoring Approaches and  Products for Areas of Climate Risk”. The primary objective will be to develop a sea-level monitoring product that communicates how daily-to-seasonal fluctuations of coastal water levels evolve with respect to the longer-term climatology. In addition to monitoring extreme sea levels,  the product will also aid in understanding the processes contributing to sea level anomalies.  Deliverables will include a near-real-time assessment of high sea-level events affecting the U.S.  Coast. Product development will complement NOAA environmental monitoring and reporting efforts such as the NOS CO-OPS seasonal High Tide Bulletin and Coastal Inundation  Dashboard, as well as the NESDIS NCEI Climate Monitoring page; the latter of which currently does not include a coastal sea level component. To aid in the transition-to-operations process, we will utilize common datums and epochs established by NOS, as well as indicate location-specific water level thresholds associated with coastal hazards established by NOAA. The new monitoring product will support NOAA’s long-term goals to increase climate intelligence concerning “weather and climate extremes” as well as “coasts and climate resilience”.