Predicting the Storm Surge Threat of Hurricane Sandy with the National Weather Service SLOSH Model

Numerical simulations of the storm tide that flooded the US Atlantic coastline during Hurricane Sandy (2012) are carried out using the National Weather Service (NWS) Sea Lakes and Overland Surges from Hurricanes (SLOSH) storm surge prediction model to quantify its ability to replicate the height, timing, evolution and extent of the water that was driven ashore by this large, destructive storm. Recent upgrades to the numerical model, including the incorporation of astronomical tides, are described and simulations with and without these upgrades are contrasted to assess their contributions to the increase in forecast accuracy. It is shown, through comprehensive verifications of SLOSH simulation results against peak water surface elevations measured at the National Oceanic and Atmospheric Administration (NOAA) tide gauge stations, by storm surge sensors deployed and hundreds of high water marks collected by the U.S. Geological Survey (USGS), that the SLOSH-simulated water levels at 71% (89%) of the data measurement locations have less than 20% (30%) relative error. The RMS error between observed and modeled peak water levels is 0.47 m. In addition, the model’s extreme computational efficiency enables it to run large, automated ensembles of predictions in real-time to account for the high variability that can occur in tropical cyclone forecasts, thus furnishing a range of values for the predicted storm surge and inundation threat

Accuracy assessment of ASTER, SRTM, ALOS, and TDX DEMs for Hispaniola and implications for mapping vulnerability to coastal flooding

Digital elevation models (DEMs) derived from remote sensing data provide a valuable and consistent data source for mapping coastal flooding at local and global scales. Mapping of flood risk requires quantification of the error in DEM elevations and its effect on delineation of flood zones. The ASTER, SRTM, ALOS, and TanDEM-X (TDX) DEMs for the island of Hispaniola were examined by comparing them with GPS and LiDAR measurements...The TDX DEMs deliver high resolution global DEMs with unprecedented elevation accuracy, hence, it is recommended for mapping coastal flood risk zones on a global scale, as well as at a local scale in developing countries where data with higher accuracy are unavailable

Hurricane Earl: A Case Study for the NHC Storm Surge Toolbox

2011 Hurricane Worksho

Storm Surge Specialist

2011 Hurricane Worksho

An Analysis of Hurricane Debby (2000) and the Impact of Vertical Shear on the GFDL Forecast Performance.

The need for improved tropical cyclone (TC) intensity guidance has never been greater given recent upward population trends in coastal areas. The difficulty in forecasting rapid intensity change remains one of the more challenging aspects of TC forecasting and was recently highlighted by the unexpected weakening of Hurricane Debby (2000) along the northern coast of Hispaniola on August 23, 2000. To address the need for improved understanding of rapid intensity change and the ability of dynamical TC models to accurately forecast intensity, a three-dimensional dynamical TC model (GFDL) is analyzed during the lifecycle of Debby. This was accomplished by first performing a comprehensive observational analysis making use of observed in-situ data as well as remotely sensed satellite data and derived products. Results from this analysis indicate that rapidly increasing vertical shear was the primary catalyst for the sudden weakening. Accordingly, vertical shear was analyzed within several operational simulations of the GFDL model near the time of weakening. This was accomplished by comparing the GFDL initial and forecast intensity with the National Hurricane Center official best track data as well as comparing the GFDL vertical shear with the AVN global analysis. Deviations in the GFDL intensity and vertical shear from the analysis data were considered to represent forecast error. These errors were then analyzed further by comparing the GFDL model forecast environmental wind field with a suite of observed data including GOES-8 satellite-derived winds, NOAA G-IV dropwindsondes, and upper-air observations supplemented by the GFDL initial analysis (F00). Results indicate that errors in vertical shear were nearly coincident with deviations in observed intensity versus forecast intensity. These deviations were primarily the result of a misrepresentation of the upper-level flow in the model due to an overdeveloped downstream upper-level ridge. Additionally, an erroneous anticyclone developed over the model storm in several cases, resulting in significant weakening of the upper level westerly flow and associated vertical shear. In this case, the downstream anticyclone was more intense and closer to the storm in nearly all simulations analyzed. These findings are similar to previous studies where a storm to environment interaction has been identified as the result of redistribution of latent heat release due to convection and the downstream advection of the associated low Potential Vorticity (PV) outflow. The misrepresentation of convection and the associated effects on the surrounding environment is identified as the primary factor for both track and intensity forecast errors by the GFDL model during Debby

Environmental influences on tropical cyclone structure and intensity: A review of past and present literature

61-74Tropical Cyclone (TC) track forecast skill has shown a steadily increasing trend in the north Atlantic basin over the last decade in contrast to little or no improvement in intensity forecast skill. This is attributable in part to a lack of in-situ observations to measure important inner-core processes and the inability of current operational numerical models to accurately resolve the inner-core dynamics. Consequently, much is unknown about TC intensity change, and the most skillful intensity forecasting techniques still rely upon climatology and persistence. The forecasting of rapid changes in intensity has been particularly difficult. The need for improved TC intensity forecasts has never been greater due to rapidly increasing population in coastal communities. This is the motivation for the present review, which seeks to discuss our current knowledge and highlight the most fruitful areas for future work. This is accomplished through a literature review of past and present research with emphasis on current gaps in knowledge

Hurricane Earl: A Case Study for the NHC Storm Surge Toolbox

2011 Hurricane Worksho