Estimating the likelihood of rapid intensification in the Atlantic and E. Pacific basins using SHIPS model data

The National Hurricane Center has identified obtaining guidance on the timing and magnitude of episodes of rapid intensification as one of the highest operational tropical cyclone forecasting priorities. In an effort to provide a tool to aid in the forecasting of rapid intensification, an index for estimating the probability of rapid intensification has been developed as part of the NOAA Joint Hurricane Testbed. The rapid intensification index employs 5 large-scale and 2 satellite-derived inner-core predictors from the SHIPS model to estimate the probability of rapid intensification for the 24-h period commencing at t=0. The 2005 version of the rapid intensification index differed from that used in previous seasons in a few areas. First, the threshold for rapid intensification was lowered slightly from a maximum sustained wind increase threshold of ≥ 30 kt in 24 h employed previously to a threshold of ≥ 25 kt in 24 h for the 2005 season. Also, the methodology for deriving the index was modified so that that the contributions from each of the rapid intensification predictors represented a scaled value between 0 and 1 rather than simply a 0 or 1 as had been employed in the prior version of the index. Both of these changes were implemented since sensitivity tests performed on both dependent and independent data showed that these modifications yielded increased forecast skill. The revised version of the rapid intensification index was run in real-time during the 2005 Hurricane season in both the Atlantic and E. Pacific basins and the output was provided to the National Hurricane Center. A verification of the 2005 real-time forecasts will be presented and new efforts to improve the index using discriminant analysis will be discussed at the conference.