Employing Hurricane Wind Probabilities to Enhance Local Forecasts and Improve Guidance for Decision-Makers

During the 2005 hurricane season, the Tropical Prediction Center (TPC) produced experimental gridded tropical cyclone wind speed probabilities for 34 knot, 50 knot, and 64 knot winds through 120 hours during operational forecast cycles for active systems in the Atlantic Basin. The probabilities were based on the official TPC track, intensity, and wind radii forecast, and incorporate average error statistics for those forecast variables during recent years. They were produced in interval and cumulative form for each successive 12-hour forecast increment. In an effort to examine their potential value, the Weather Forecast Offices (WFOs) at Miami (MFL) and Melbourne (MLB) collaboratively developed and tested several unique applications to enhance local forecasts and improve guidance information for decision-makers. Preliminary results have been promising and are being shared with the community for evaluation. This presentation will focus on aspects which enable WFO forecasters to offer expressions of uncertainty for tropical cyclone winds as conveyed within alpha-numeric and graphic forecast products.

The interval-based probabilities were used to trigger enhanced wording which responsibly convey wind speed uncertainties within particular text products such as the Zone Forecast Product (ZFP) and the Coastal Waters Forecast (CWF). The enhanced wording was added within offline versions of these official products. As such, the automated text formatter was able to express when hurricane or tropical storm conditions were "EXPECTED", "LIKELY", or "POSSIBLE" according to the temporal period. If transitioned, it would help alleviate sensitivities surrounding the current deterministic-only approach for depicting the wind during tropical cyclone forecast situations. More so, it would foster greater forecast consistency with TPC and adjacent WFOs, while reducing the workload for manual text editing. Similarly, additions and improvements to tabular products such as forecast matrices can also be offered when tropical cyclones threaten the forecast area.

To enhance certain graphical products, a parallel effort was undertaken using the cumulative-based probabilities for deriving an automated first-guess of the local wind threat. In tropical cyclone watch and/or warning situations, both MFL and MLB issue an experimental wind threat graphic to benefit general users who are seeking decision-making information. In practice, a first-guess wind threat graphic was created by compositing the probability of exceeding the 34-, 50-, and 64 knot thresholds. Utilizing the cumulative-based probabilities promoted increased efficiency during product preparation, and allowed forecasters to spend more time adding value to the final product. Lastly, both probability sets (interval and cumulative) were used to directly create WFO-centric graphical depictions of wind speed probabilities to further accommodate specialized decision-making.