From the “Statement Heard Around the World” to Hurricane Threats and Impacts: The Evolution of Communicating Potential Impacts and Safety Messages since Katrina

On August 28th, 2005, the National Weather Service (NWS) Forecast Office in Slidell, LA, used vivid language within local statements to describe the impending danger to life and property associated with the arrival of Hurricane Katrina. Safety messages containing uniquely purposed wording were disseminated to urgently express the extreme aspects of possible impacts. They included concerns from both natural and made-made influences relative to the approaching wind and surge hazards. Impassioned messages emanated from the expected strike zone and reached outward to local populations at risk, but also to an entire nation and beyond. Post-event reports credited these messages for helping to prompt the evacuation of nearly ninety percent of the residents within New Orleans' metropolitan area.

At that time, guidance used to support local decision-making was largely deterministic (e.g. forecast error not taken in to account) and local messaging was mostly in the form of text-only products. Although experimental wind speed probability data were available from the National Hurricane Center, in practice uncertainty was typically considered through empirical methods, modulated by personal experience. When the enhanced messages were first issued, the forecast was for high winds to arrive within the 18-24 hr time frame. Given an average measure of inherent forecast error, there remained a realistic chance for false alarm. The vivid language mainly spotlighted devastating to catastrophic wind impacts that could result from equivalent Category 4 force wind. While Katrina's impacts upon New Orleans were indeed extreme, they were actually due to a combination of both wind and storm surge flooding.

This presentation will detail how the NWS communicates hurricane-related potential impacts and how this effort has evolved in the ten years since Katrina. It will review the circumstances which originally prompted the enhanced messaging, as well as the strengths and shortcomings in context of current expectations. It will also outline the evolution of service improvements now delivered by local forecast offices highlighting methods which more consistently account for forecast uncertainty. It will examine the latest assessment techniques for hurricane wind and surge that result in a more comprehensive awareness of the threat situation, and how this information can be more effectively communicated. Lastly, it will explore the Hurricane Threats and Impacts initiative beyond the provision of stand-alone text. It will highlight the importance of integrating graphics formatted for GIS capabilities, as well as the availability of threat grids within the National Digital Forecast Database. The value of locally refined potential impacts statements leading to effective safety messaging will also be considered.