What Is Six Hours Worth? The Impact of Lead Time on Tropical-Storm Preparation Decisions

Emergency managers must make high-stakes decisions regarding preparation for tropical storms when there is still considerable uncertainty regarding the storm’s impacts. Forecast quality improves as lead time until the forecast events declines. Reducing the lead time required for preparation decisions can substantially improve the quality of forecasts available for decision making and thereby, reduce the expected total costs of preparations plus storm damage. Measures of forecast quality are only indirectly linked to their value in preparation decisions and changes in the parameters of those decisions—in particular lead time. This paper provides decision-relevant measures of the quality of recent National Hurricane Center forecasts from the 2014–2018 seasons, which can be used to evaluate reductions in decision lead time in terms of false alarm rate, missed detections, and expected annual costs. For decision makers in some regions with decision lead times of 48–72 hours—typical for evacuation decisions—every 6-hour reduction in required lead time can reduce the false alarm rate by more than 10%.