33WAF/29NWP A Collaborative Approach to Improving the National Blend of Models Sustained Wind Speed and Gust Forecasts for the Coastal Waters of the Florida Keys

Accurate surface sustained wind speed and gust forecasts are critical to the marine community in the Florida Keys. The demographic makeup of the Florida Keys marine community is quite diverse, ranging from liveaboards, to federal entities such as the United States Coast Guard, to recreational and commercial fishermen, to tourists with varying degrees of marine experience. In addition, approximately 40% of the world’s maritime commercial goods traverse the Straits of Florida south of the island chain. Due to increasing demands for Impact-Based Decision Support Services (IDSS), the National Weather Service (NWS) recently converted to the use of a standard National Blend of Models (NBM) for baseline forecast grid production. Forecasters must then use local expertise and scientific meteorological reasoning to fine-tune this NBM grid output. The NBM uses the Unrestricted Mesoscale Analysis (URMA), which incorporates observational data to bias correct a first-guess field generated by mesoscale numerical weather prediction output. Forecasters at the Key West NWS have shown the bias-corrected URMA and the resulting NBM output often result in a negative wind speed bias offshore, mainly due to the influence of land and nearshore marine observations.

Recently, forecasters from the Key West NWS hosted a workshop with representatives from Southern Region Headquarters’ Science and Technology Services Division (STSD) and the Meteorological Development Laboratory (MDL) to discuss some of the wind speed forecast challenges for the Florida Keys as well as potential solutions. Key West NWS forecasters presented case studies to the MDL developers highlighting NBM bias over the offshore marine locations, particularly during events with higher observed wind speeds. The collaborative discussion ultimately opened a direct line of communication between NWS forecasters in Key West and MDL, with a common goal of eliminating the uneven spatial bias in NBM output observed along other coastal regions of the United States. Currently, the Environmental Modeling Center (EMC) is executing parallel runs of the URMA, which exclude selected land and nearshore marine observations. Using the output of the parallel runs of the URMA, MDL then executes parallel runs of the NBM to test reduction in the negative wind speed bias offshore. Moreover, MDL developers are considering alternate NBM real-time analysis/verification sources (e.g., direct high-resolution numerical weather prediction model output). Forecasters from the Key West NWS and MDL developers are collaboratively evaluating this experimental analysis and verification. The ultimate goal of this project is to improve wind speed and gust forecasts for the Keys in the next NBM release in 2025, which will serve as a much better starting point for routine forecast generation.