The new frontier: operational tropical cyclone forecasts beyond five days

Operational warning agencies such as the National Hurricane Center produce tropical cyclone (TC) track and intensity forecasts that cover a five-day forecast window. However, this approach does not maximize the current state of TC predictability, since these advisories are not issued prior to TC genesis and are artificially constrained to five days. If the actual reservoir of TC predictability is realized by providing pre-TC genesis track forecasts and allowing the dynamical uncertainty of the future atmospheric state to constrain the forecast time window, this new forecasting approach would provide several days of additional lead time for disaster mitigation. To illustrate how this forecast strategy could be implemented, the performance statistics of daily probabilistic outlooks for 2008-2010 are reviewed relative to the observed level of TC activity. These outlooks cover a 15-day forecast period and are provided for the Gulf of Mexico, Caribbean Sea, and Main Development Region. By providing regional probabilistic outlooks of TC activity, this forecast format allows the end-user to conduct their own cost-benefit analysis to hedge against the forecast level of TC risk. The potential for TC forecasts out to one month is also discussed using ensemble-based TC track forecasts from the ECMWF Monthly Forecast System. These intraseasonal outlooks can be calibrated to provide skillful forecasts relative to the climatological likelihood of TC activity and can be designed to provide landfall risk information for coastal locations throughout the North Atlantic.