About WPC's Tropical Advisories

Issuance of Tropical Cyclone Advisories by WPC:

Under NWS Directive 10-601 Section 6.9.2.2, "The WPC will issue public advisories after NHC discontinues its advisories on subtropical and tropical cyclones that have moved inland, but still pose a threat of heavy rains and flash floods in the conterminous United States or adjacent areas within Mexico which affect the drainage basins of NWS River Forecast Centers. The last NHC advisory will normally be issued when winds in an inland tropical cyclone drop below tropical storm strength, and the tropical depression is not forecast to regain tropical storm intensity or re-emerge over water. WPC advisories will terminate when the threat of flash flooding has ended."

Content of an WPC Tropical Cyclone Advisory:

A Tropical Cyclone Advisory issued by WPC provides users with meteorological information, primarily the potential of heavy rain and flash flooding, from decaying subtropical or tropical systems which have moved inland. The contents of the WPC Tropical Cyclone Advisory are outlined below:

Headline describing the current event
Current watches, warnings, and advisories
Description of the current location, maximum sustained winds, movement, and minimum central pressure of the system
Table(s) documenting the precipitation induced by the system
Description of the evolution and forecast for the system
A statement including the time the next WPC advisory will be issued or, if it is the last WPC advisory, where to find subsequent information on the system
A forecast for the position of the circulation center so long as the system is a flash flooding threat for the Continental United States

WPC Point Forecasts for Tropical Cyclones:

According to the NWS directive passed at the 2005 NOAA Hurricane Conference, "WPC will provide forecast points within their TCP, out through 120 hours (if necessary), at the same time steps as NHC (the National Hurricane Center), and issued at the normal advisory times, as long as the system is expected 1) to have an identifiable surface low and 2) to provide a significant precipitation threat to the continental United States." Forecast positions will cease when (a) a system is forecast to be absorbed into another meteorological feature (denoted by the clarifier"ABSORBED" within the forecast points section of the advisory), (b) the circulation center at the surface is forecast to dissipate (denoted by the clarifier "DISSIPATED", (c) the system is forecast to move offshore and no longer provide a flash flooding threat to the Continental United States (denoted by the clarifier "OVER WATER"), or (d) the system is forecast to move into Canada or Mexico and no longer provide a flash flooding threat in the Continental United States (denoted by the clarifiers "OVER MEXICO or OVER CANADA").

In all cases, the issuance of Tropical Cyclone Public Advisories by WPC will cease when the flash flooding threat no longer exists in the Continental United States, despite the presence of a discernable surface circulation within the Continental United States. In the forecast period, if the flash flooding threat is expected to cease over the Continental United States but a discernable circulation center is expected to move into Canada, Mexico, or offshore, WPC will issue only one forecast point outside of the Continental United States past the point when the system is no longer a flash flooding threat in the Continental United States.

Example: The surface circulation center of a system is forecast to move northward from New York state into Southern Quebec, but the threat of flash flooding over the Continental United States is over, and this is the last Tropical Cyclone Advisory to be written by WPC. The forecast points will look as follows:

FORECAST POSITIONS AND MAX WINDS

INITIAL     30/1500Z 43.5N  74.5W    30 KT
12HR VT     31/0000Z 46.3N  73.4W    25 KT...OVER CANADA
24HR VT     31/1200Z...OVER CANADA