Assessing the predictability of tropical cyclone rapid intensification as a function of forecast lead-time using the SHIPS rapid intensification index

The current operational version of the rapid intensification index (RII) uses large-scale predictors from the SHIPS model to estimate the 24-h probability of rapid intensification (RI) in both the Atlantic and eastern North Pacific basins using linear discriminant analysis. Although recent results indicate that the RII is generally skillful its utility is somewhat limited since it was developed exclusively for a lead-time of 24-h, has only limited skill (particularly in the Atlantic basin), and is entirely probabilistic in nature. Thus, research to improve the usefulness of the operational RII is currently being conducted in several different areas. First, new versions of the RII are being developed for the added lead times of 12-h, 36-h and 48-h. Second, efforts to refine recently developed methods for generating an ensemble based RII and for utilizing the probabilistic RII output to make deterministic intensity forecasts are also underway. Finally, methodology for incorporating satellite-derived microwave imagery into the RII is also being developed. Although as is described above research to improve the operational RII is currently being conducted in several different areas, this abstract will focus on current efforts to develop versions of the RII for the additional lead times of 12-h-, 36-h and 48-h. To accomplish this task, the experimental linear discriminant analysis version of the RII that was developed as part of a recently completed Joint Hurricane Testbed (JHT) proposal will be employed. Since this newly developed version of the RII utilizes mainly environmental predictors, the predictability of RI on the aforementioned times scales utilizing large-scale information can be assessed. We note that the predictability of the RII at the longer lead times (i.e. beyond 24 h) is of particular interest now that that the National Hurricane Center (NHC) has extended tropical cyclone watch and warnings lead-times out to 48-h.