TC wind radii analysis and forecasting background

As a follow up to a recent call with the TC wind collaboration team, I put some slides together that describe the methodology and tools (or lack thereof) for analysis and forecasting of the quadrant wind radii for tropical cyclones.  These radii represent the largest extent from the center in each quadrant where winds of 34, 50, or 64 would be found.  There may also be gaps between winds of a given threshold in the quadrant.

Tropical cyclone wind field structure is by far the most uncertain analysis and forecast parameter.  In the open ocean with very limited surface wind observations, analyzed wind radii are based on empirical relationships between intensity and the radii or the satellite appearance of the cyclone.  Even in situations where aircraft data are available, SFMR and flight-level winds extend only along radials under the aircraft track and provide a single value of the wind radii for that quadrant (a single aircraft only samples about 2% of the wind field in a standard alpha pattern).

coverage of SFMR winds from a typical aircraft alpha pattern

Forecasting of wind radii is tied closely to the intensity forecast, which has an average error of about 20 kt by 48-72 h.  Due to a lack of skill in the dynamical models, we typically lean heavily toward the climatology/persistence models when making radii forecasts.  Given the lack of data to routinely even analyze wind radii with any confidence, NHC does not attempt to verify its wind radii forecasts.

graphical wind radii forecast tool showing quadrant radii and various forecasts aids

These analyses and forecasts are critical inputs into the TCM wind tool that takes the radii out of the tropical cyclone forecast/advisory product (the TCM) and creates a graphical representation for the WFOs to work with when making their gridded wind forecasts. The wind radii analysis also serve as one of the inputs for the Monte Carlo tropical cyclone wind speed probabilities product.

I hope this summary is helpful as we move forward on this project.   If you have any questions or comments on this issue, please leave them here, or shoot me an email at Michael.J.Brennan@noaa.gov.

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2 Responses to TC wind radii analysis and forecasting background

  1. bptyner says:

    Thanks, Mike for putting together the slides. I think it does a good job highlighting the relatively high uncertainty associated with creating the maximum wind radii forecasts that is used for the initial condition for the TCMWindTool. In particular, I find the empirical sources for radii quite interesting. Do you happen to have a reference for these noted empirical relationships?

  2. Pingback: CSTAR Update – One Year Since the Kickoff Workshop | CIMMSE

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