potential_tropical_cyclone

Potential Tropical Cyclone:

Since 2017, has the option to issue advisories, watches, and warnings for disturbances that are not yet a tropical cyclone, but which pose the threat of bringing tropical storm or hurricane conditions to land areas within 48 hours. Under previous longstanding NWS policy, it has not been permitted to issue a hurricane or tropical storm watch or warning until after a tropical cyclone had formed. Advances in forecasting over the past decade or so, however, now allow the confident prediction of tropical cyclone impacts while these systems are still in the developmental stage. For these land-threatening “potential tropical cyclones”, NHC will now issue the full suite of text, graphical, and watch/warning products that previously has only been issued for ongoing tropical cyclones.

Potential tropical cyclones will share the naming conventions currently in place for tropical and subtropical depressions, with depressions and potential tropical cyclones being numbered from a single list (e.g., “One”, “Two”, “Three”, …, “Twenty-Three”, etc.). The assigned number will always match the total number of systems (tropical cyclones, subtropical cyclones, or potential tropical cyclones) that have occurred within that basin during the season. For example, if three systems requiring advisories have already formed within a basin in a given year, the next land-threatening disturbance would be designated “Potential Tropical Cyclone Four”. If a potential tropical cyclone becomes a tropical depression, its numerical designation remains the same (i.e., Potential Tropical Cyclone Four becomes Tropical Depression Four).

Potential tropical cyclone advisory packages (i.e., the Public Advisory, Forecast/Advisory, Discussion, Wind Speed Probability Product, etc., along with all the standard tropical cyclone graphics) will be issued at the standard advisory times of 5 AM, 11 AM, 5 PM, and 11 PM EDT. Three-hourly Intermediate public advisories will be issued for potential tropical cyclones at 2 AM, 8 AM, 2 PM, and 8 PM EDT when watches or warnings are in effect. The product suite will include a five-day track and intensity forecast just as is done for ongoing tropical cyclones. In addition, the Potential Storm Surge Flooding Map and Storm Surge Watch/Warning graphic would be issued for these systems when appropriate.

Advisory packages on potential tropical cyclones will be issued until watches or warnings are discontinued or until the threat of tropical-storm-force winds for land area sufficiently diminishes, at which point advisories would be discontinued. However, if it seems likely that new watches or warnings would be necessary within a short period of time (say 6-12 hours), then advisories could continue for a short time in the interest of service continuity. Once a system becomes a tropical cyclone, the normal rules for discontinuing advisories will apply. Potential tropical cyclone advisories will not be issued for systems that pose a threat only to marine areas.

Because NHC will be issuing its normal graphical products depicting the five-day forecast track and uncertainty cone for potential tropical cyclones, to avoid potential confusion the Graphical Tropical Weather Outlook will no longer display a formation area for these systems.