Future Predictions of U.S. East Coast Winter Storms and Associated Impacts

The Northeast U.S. is particularly vulnerable to extreme weather from winter cyclones (heavy precipitation, wind, and storm surge). This presentation will highlight the future changes (up to year 2098) of cool season (November through March) extratropical cyclones over the Northeast U.S. using the Coupled Intercomparison Modeling Project (CMIP5) as well as an ensemble of Weather Research and Forecasting (WRF) members down to 20-km grid spacing downscaled using NCEP reanalysis and a few CMIP5 models. The 6-h output from CFSR (Climate Forecast System Reanalysis) and CMIP5 models was used to provide initial and boundary conditions for the historical and future WRF runs, respectively. Some processes responsible for the model differences and future cyclone changes in cyclone intensity along the U.S. East coast were diagnosed using storm-relative composites of temperature, winds, precipitation, etc… within a 20 x 20 degrees box around each cyclone center. For example, during 2069-2098 (for RCP8.5), there is a significant increase in cyclone-relative precipitation, especially over continent at middle and high latitudes (20-40% by the later 21st century). This precipitation increase is mainly for the strong and moderate cyclones, which get more intense in several models, therefore suggesting the importance of latent heating with the additional moisture in a warmer climate. Since many of the CMIP5 models do a realistic job with extratropical cyclones, we developed a generalized parametric downscaling technique to create a point-based storm surge time series for the cool season using 6-h CMIP5 data. The statistical model for New York City is trained and evaluated using Oct-March 10-m wind and mean sea level pressure from the NARR renanalysis between 1979-2012. Overall, there is a significant decrease in the ensemble mean number of >= 1.0 m surge events. However, if one includes a sea-level rise of at least 0.5 m during the next several decades, all models have a significant increase in the number of coastal flooding events.