Biases and limitations in the estimation of hurricane intensity.
While the average errors of tropical cyclone track forecasts steadily decreasing over the last two decades, intensity forecasts have only marginally improved. For North Atlantic, the 24-hour intensity forecast has shown no improvement, with mean errors of peak wind speed forecasts remaining around 10 knots for the last 20 years. Some studies have suggested that, given the current observing system, the actual peak wind speed cannot be measured to an accuracy greater than about 10 knots. In this study, we use the Observing System Simulation Experiment (OSSE) to test the limitations of observing systems to capture the peak wind speed occurring within a tropical storm or hurricane. The data set is provided by a 1-km resolution simulation of an Atlantic hurricane with surface wind speeds saved every 10 seconds. An optimal observing system consisting of a dense field of fixed anemometers is placed in the path of the storm: this provides a perfect measurement of the peak 1-minute wind speed. A realistic observing system consisting of a small number of anemometers is sampled and compared to the truth provided by the optimal observing system. Results show that a single, perfect anemometer experiencing a direct hit by the right side of the eyewall will still underestimate the actual peak intensity by 10-20%. Even an unusually large number of anemometers (e.g., 3-5) experiencing direct hits by the storm will together underestimate the peak wind speeds by 5-10%. However, the peak intensity of just one or two anemometers will provide, on average, a good estimate of the true peak intensity averaged over several hours, which is in fact more consistent with operational definitions of intensity.
Dr. Nolan obtained his undergraduate and graduate degrees at Harvard University. Before coming to the University of Miami in 2002, he held research positions at UC Berkeley, Colorado State, and Princeton University. The majority of his research has been on the dynamics of hurricanes, with emphasis on their formation and intensification. He has also investigated the dynamics of convection in the tropics and the fluid dynamics of tornadoes.