Constraints in Dvorak Wind Speed Estimates: How Quickly Can Hurricanes Intensify?

Abstract

AbstractThe Dvorak technique is used operationally by meteorological agencies throughout the world for estimating tropical cyclone intensity and position. The technique consists of constraints that put a maximum threshold for which the final T-number, relating directly to intensity, can change during a certain time interval (6, 12, 18, and 24 h). There are cases when these constraints could be broken, especially during rapid intensification. This research tests whether the constraints used for intensity change are warranted or need to be changed. A database of cases with the largest intensity changes for 2000–17 Atlantic tropical cyclones was compiled. A reconnaissance or scatterometer “fix” is required within 3 h of both the beginning and ending of the period for each case to inform the best track and to be included for analysis. Dvorak classifications from the Tropical Analysis and Forecast Branch are noted for each case, which includes the initial and final T-numbers, current intensity numbers, and data T-numbers. Statistical parameters, including correlations, intensity errors, absolute intensity errors, root-mean-square errors, and significance tests are calculated and analyzed for each period. Results suggest that the T-number constraints for the 18- and 24-h periods could be increased to a 2.5 and a 3.0, respectively. However, results also suggest that the constraints for the 6- and 12-h time intervals should remain the same.