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A Climatology-Based Forecast Tool for Coastal Flooding in the Low Country

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  • 1 a College of Charleston, Charleston, South Carolina
  • | 2 b NOAA/NWS/Weather Forecast Office, Columbia, South Carolina
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Abstract

Coastal nuisance flooding has increased by an order of magnitude over the past half century, but the National Weather Service has a limited suite of statistical tools to forecast it. Such a tool was developed using coastal flood events from 1996 to 2014 in Charleston, South Carolina, that were identified and classified by prevailing synoptic conditions based on composite mean sea level pressure anomalies. The synoptic climatology indicated low-level northeasterly winds dominated the forcing in anticyclonic and cyclonic events, while a southeasterly surge was the main forcing component for frontal events. Tidal anomalies between flood events and previous low tides were used to create linear regression models for each composite classification studied for forecasting levels of coastal flood magnitude. Beta tests using data from 2018 to 2019 confirmed the effectiveness of the models with RMSE values less than 0.3 ft (9 cm) and MAE values less than 0.25 ft (7.6 cm) for each event type. The veracity of the methods was further verified by a multiple-day case study from November 2018, where the model was tested against both statistically predicted heights and heights based on the NOAA extratropical storm surge (ETSS) model (version 2.2). The RMSE and MAE for the statistical model were 0.18 and 0.15, respectively, while the same values for the ETSS model were 0.28 and 0.23, respectively.

Significance Statement

Nuisance coastal flooding in Charleston, South Carolina, occurs numerous times per year and causes disturbances in traffic, commerce (financially and socially), and human health. Charleston has spent hundreds of millions of dollars (and counting) on drainage projects and seawall raisings. Furthermore, flooding has caused gross damages and lost wages of nearly $2 billion. As global sea levels continue to rise, the annual number of coastal flooding events in Charleston continues to increase. This climatology-based forecast tool will aid forecasters in the accurate prediction of tides that cause the inundation in the Charleston area as well as support the timely issuance of coastal flood advisories, watches, and warnings to help protect life and property.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Joseph Coz, joeycoz@gmail.com

Abstract

Coastal nuisance flooding has increased by an order of magnitude over the past half century, but the National Weather Service has a limited suite of statistical tools to forecast it. Such a tool was developed using coastal flood events from 1996 to 2014 in Charleston, South Carolina, that were identified and classified by prevailing synoptic conditions based on composite mean sea level pressure anomalies. The synoptic climatology indicated low-level northeasterly winds dominated the forcing in anticyclonic and cyclonic events, while a southeasterly surge was the main forcing component for frontal events. Tidal anomalies between flood events and previous low tides were used to create linear regression models for each composite classification studied for forecasting levels of coastal flood magnitude. Beta tests using data from 2018 to 2019 confirmed the effectiveness of the models with RMSE values less than 0.3 ft (9 cm) and MAE values less than 0.25 ft (7.6 cm) for each event type. The veracity of the methods was further verified by a multiple-day case study from November 2018, where the model was tested against both statistically predicted heights and heights based on the NOAA extratropical storm surge (ETSS) model (version 2.2). The RMSE and MAE for the statistical model were 0.18 and 0.15, respectively, while the same values for the ETSS model were 0.28 and 0.23, respectively.

Significance Statement

Nuisance coastal flooding in Charleston, South Carolina, occurs numerous times per year and causes disturbances in traffic, commerce (financially and socially), and human health. Charleston has spent hundreds of millions of dollars (and counting) on drainage projects and seawall raisings. Furthermore, flooding has caused gross damages and lost wages of nearly $2 billion. As global sea levels continue to rise, the annual number of coastal flooding events in Charleston continues to increase. This climatology-based forecast tool will aid forecasters in the accurate prediction of tides that cause the inundation in the Charleston area as well as support the timely issuance of coastal flood advisories, watches, and warnings to help protect life and property.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Joseph Coz, joeycoz@gmail.com
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