Tropical Storm Andrea Provided an Opportunity to Test New CSTAR Based Tropical Cyclone Wind and Wind Gust Tools


Map of WFOs participating in the evaluation of the experimental tropical wind and wind gust methodology.

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.


Map of the NHC TCM four quadrant tropical storm force wind radii from 15 UTC 06 June 2013.

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.


Regional depiction of 48-hour forecast winds from the various WFOs across the mid-Atlantic valid at 18 UTC on 07 June 2013 when the center of Tropical Storm Andrea was forecast to move over North Carolina. Only three WFOs were testing the new methodology during Andrea (ILM, MHX, and RAH) but the forecasts from these offices show the potential improvement with this methodology.


An experimental forecast grid shows the maximum forecast sustained winds across portions of the mid-Atlantic valid during the entire period in which Tropical Storm Andrea was forecast to move over North Carolina. This maximum sustained wind grid is a part of the new methodology that was tested at ILM, MHX, and RAH

A snapshot of internal NWS chatting dialog during Tropical Storm Andrea which shows some of the collaboration that takes place between WFOs.



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1 Response to Tropical Storm Andrea Provided an Opportunity to Test New CSTAR Based Tropical Cyclone Wind and Wind Gust Tools

  1. Pingback: A Wind Gust Factor Database of Marine Observations from 10 Tropical Cyclones | CIMMSE

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