A revised rapid intensification index for the Atlantic and E. Pacific basins

The SHIPS rapid intensity index has undergone numerous changes since it was first provided in real time to the National Hurricane Center during the 2001 Atlantic Hurricane Season. The original version compared the t=0 h magnitude of 5 large-scale predictors from the SHIPS model to thresholds that had been determined previously from a sample of rapidly intensifying Atlantic basin systems to estimate the probability of rapid intensification (defined as a 24 h change > 30 kt over the next 24 h). In succeeding versions, 2 GOES satellite-derived inner-core predictors were added to the index (bringing the total number predictors used to 7) and several of the predictors were averaged over the entire 24 h period. The rapid intensity threshold was also lowered slightly to 25 kt. Another version of the index was also developed for the E. Pacific, since the original rapid intensity index was developed exclusively for the Atlantic basin. More recently, the method for deriving the index was modified so that that the contributions from each of the predictors represented a scaled value between 0 and 1 rather than either a 0 or 1 as had been employed in the original threshold version. These scaled values were subsequently weighted to determine the relative importance of each to rapid intensification utilizing linear discriminant analysis. Finally, an 8th predictor determined from satellite altimetry data was added and the index was re-derived for additional rapid intensity thresholds. This new version of the rapid intensification index will be verified for an independent set of cases and compared to other operational intensity forecast guidance and the results will be presented at the conference. The relative importance of the various predictors will also be assessed for each rapid intensity threshold for both the Atlantic and E. Pacific basins.