The former Hurricane Isaias has now been designated a Post-Tropical Cyclone by the National Hurricane Center.
But what is that?
A post-tropical cyclone is a former tropical storm or hurricane that no longer has the characteristics needed to be classified as a tropical cyclone. The designation describes a change in the storm’s structure; it does not necessarily mean the danger has passed. Post-tropical cyclones can still produce heavy rain and powerful winds. nhc.noaa.gov
The National Hurricane Center identifies two specific types:
- Extratropical cyclone: A storm that gets its primary energy from temperature differences between warm and cold air masses. It can retain winds of tropical storm or hurricane strength.
- Remnant low: A system that has lost the organized thunderstorm activity needed for tropical classification and has sustained winds below tropical storm strength — roughly 39 mph. nhc.noaa.gov
For residents, the important distinction is that “post-tropical” is not an all-clear signal. A storm’s rainfall and wind forecasts remain more useful measures of its potential danger than the classification alone.
About the National Weather Service
The National Weather Service (NWS) is a federal agency within the National Oceanic and Atmospheric Administration (NOAA), part of the U.S. Department of Commerce. Its primary mission is to provide weather, water, and climate data, forecasts, and warnings to protect life and property and to enhance the national economy.
Headquartered in Silver Spring, Maryland, the NWS operates through a network of six regional headquarters and more than 100 local Weather Forecast Offices (WFOs) across the country. These offices issue weather forecasts, warnings, advisories, and watches tailored to specific geographic areas.
Metro Atlanta is served by the National Weather Service’s Atlanta/Peachtree City Weather Forecast Office, located in Peachtree City. The office issues forecasts, watches, warnings and other weather information for much of north and central Georgia, including Cobb County.
The NWS also runs specialized centers, including the Storm Prediction Center (SPC) for severe weather outlooks, the National Hurricane Center (NHC) for tropical storm tracking, the Weather Prediction Center (WPC) for national forecast guidance, and the Space Weather Prediction Center (SWPC) for solar activity that may affect Earth-based systems.
NWS forecasts and alerts are based on data from a combination of satellites, radar systems, weather balloons, surface observation stations, and computer models. The agency collaborates with emergency managers, broadcasters, government agencies, and the public to ensure that timely and accurate information is disseminated during weather events.
Its services are made available to the public at no cost, and its warnings—such as tornado warnings, flash flood alerts, and winter storm advisories—serve as official guidance for public safety and emergency response.
Editor’s note: AI was used in the production of this article. To read about how, when and why we make use of AI, read our article “How, When and Why the Cobb County Courier uses AI.”