The 2013 Atlantic hurricane season has been rather quiet, especially in terms of landfalling tropical cyclones in the United States. As we approach the peak of the hurricane season, only one storm, Tropical Storm Andrea, has impacted the southeastern United States. A Collaborative Science, Technology, and Applied Research (CSTAR) project with North Carolina State University and over a half dozen WFOs in the Southeast is examining ways to add science and improve inland wind and wind gust forecasts associated with tropical cyclones.
One outcome of this project is the development of an experimental GFE methodology in which forecasters create grids of wind reductions (from the NHC TCM guidance) and wind gust factors (applied to the wind to determine the wind gust) across the Weather Forecast Office (WFO) forecast area. The new methodology is used in the Gridded Forecast Editor (GFE) and uses two new forecast grids: the WindReductionFactor and the WindGustFactor. By providing forecasters with the opportunity to vary these two grids both spatially and temporally across the forecast area and allowing the values to be collaborated across WFO boundaries and maintained from shift to shift, improved forecasts are expected. Some of the specific advantages include:
• A more consistent and science-based process is available to the forecasters, likely producing improved wind and wind gust forecasts.
• Forecasters can more easily integrate the collective impact of boundary layer stability, friction, exposure, fetch, cold air damming, etc. into the forecast process.
• Forecasters can more easily mitigate some of the inherent disadvantages of the TCM product and the TCMWindTool including the linear interpolation of the forecast guidance and the single applied reduction factor.
• Forecasters can collaborate the reduction factor and gust factor visually in GFE , likely reducing CWA border discrepancies.
• Wind reduction and wind gust factors will carry over from shift to shift promoting continuity and diminishing the need to work through a lengthy process each time a TCM product is issued.
• Forecasters can create the reduction factors prior to the NHC guidance (TCM) arrival resulting in more timely products.
This new methodology was tested on 6 June 2013 when Tropical Storm Andrea was located in the eastern Gulf of Mexico. The image to the right shows the NHC TCM product four quadrant based tropical storm force wind radii. This coarse 12 to 24 hour guidance is what forecasters at the WFOs are tasked to use and “downscale” into 2.5 x 2.5 km gridded forecasts of hourly winds and wind gusts. During Tropical Storm Andrea, three WFOs were just starting to test this methodology (ILM, MHX, and RAH). By using this new methodology, forecasters were able to create and edit the wind and wind gust grids with more scientific integrity, were able to collaborate much more efficiently, and create a fairly consistent forecast across the boundaries of multiple WFOs. The first two images below show some of the forecast products while the last image shows some of the internal NWS chatting dialog during Tropical Storm Andrea.