Issuance of Timely Tropical Storm and Hurricane Watches and Warnings Before Tropical Cyclone Formation

The National Hurricane Center (NHC) and local National Weather Service Weather Forecast Offices (WFOs) have identified cases during the past several years in which tropical cyclones have formed and affected coastal communities within the typical tropical storm warning and watch (36 h to 48 h) lead time. Since tropical storm and hurricane warnings currently are tied administratively to NHC advisory products, there is no established mechanism to allow the issuance of these warnings until a tropical depression or storm has formed. In June 2015, Tropical Storm Bill formed so close to the Texas coast that formal tropical storm warnings were only issued about 12 hours before winds of that intensity came ashore. This is a longstanding limitation of the NWS tropical cyclone program that can hamper the public's readiness since many preparedness actions are tied to the issuance of tropical storm or hurricane warnings.

Although this type of scenario is not new, what has changed is NHC's ability to anticipate tropical cyclone development. During the past decade NHC has greatly enhanced its forecasts of tropical cyclone formation by introducing quantitative 48- and 120-hour genesis forecasts. This presentation will outline a plan in which the NWS would broaden the definition of tropical storm and hurricane watches and warnings to allow their use for disturbances that have a significant potential of becoming a tropical cyclone and risk bringing tropical-storm-force winds to land areas. To support these watches and warnings NHC would issue forecasts and advisory products for Potential Tropical Cyclones. The NWS/NHC is planning to debut this new service in 2016 or 2017.