1. Development of a Rapid Intensification Index for the Eastern Pacific Basin John Kaplan NOAA/AOML Hurricane Research Division Miami, FL and Mark DeMaria NOAA/NESDIS Fort Collins, Colorado Acknowledgements: Joint Hurricane Testbed

2. Background The present capability to predict rapid intensification (RI) remains inadequate (Keith (2000), Lilly (2002), and Kenna (2003)) and predicting RI has been ranked as one of the top forecasting priorities by the NHC Since the present intensity prediction models have not yet shown the capability to predict RI adequately, Kaplan and DeMaria (2003) have developed a simple index for predicting the probability of RI using SHIPS model output The RI index was run in real-time in the Atlantic basin from 2001-2003 as part of the JHT The Atlantic version of the RI index will be run operationally starting with the 2004 hurricane season An RI index analogous to the one developed in the Atlantic basin is being developed for the E. Pacific basin with support from the JHT

3. Cumulative Frequency distributions (1989-2002) All over-water tropical and subtropical cyclones

4. Definition of Rapid Intensification (RI) Rapid intensification (RI) is defined as the 95th percentile of all over-water 24-h intensity changes of the subtropical and tropical cyclones that developed from 1989-2002 This equates to a 24-h maximum sustained wind increase of > 15.4 ms -1 (30 kt) (Atlantic Basin) This equates to a 24-h maximum sustained wind increase of > 18.0 ms -1 (35 kt) (E. Pacific Basin)

5. 24-h tracks of the E. Pacific RI cases (N=85) (24-h change in maximum wind > 35 kt)

6. Development of the SHIPS RI index ( Kaplan and DeMaria Wea. Forecasting 2003 ) Determine SHIPS predictors for which statistically significant differences existed between the RI and non- RI cases Determine RI thresholds for all statistically significant predictors (average of all the RI cases) Compute probability of RI for each 24-h period by comparing the SHIPS predictor magnitudes to the corresponding RI thresholds Employ the 5 (Non-GOES version) and 7 (GOES version) SHIPS predictors that yielded the highest individual RI probabilities to compute a combined probability of RI Provide real-time estimates of the probability of RI with each SHIPS forecast

7. Predictors used in the 2004 Atlantic and E. Pacific versions of the RI index Previous 12 h intensity change (t=0 h) Observed sea-surface temperature (24-h mean) Maximum potential intensity - initial storm intensity (24 h mean) 850-200 hPa vertical shear from 200-800 km at (24 h mean) 850-700 hPa relative humidity from 200-800 km (24 h mean) GOES Version All predictors used in Non-GOES version PLUS –Area-averaged inner-core brightness temperature (t=0 h) –Standard deviation of inner-core brightness temperature (t=0 h) Non-GOES Version

8. Performance of the GOES version of the RI index for the dependent sample (1995-2002)

9. Brier Score = 1/N ∑ (F-E) 2 N = number of forecasts F= forecast probability (where 50% is expressed as 0.5) E = Event probability (where E=1 when RI occurred and 0 when it did not) The Brier score was computed both for the RI index using the forecast probability of RI values and for climatology using the climatological probability of RI N i=1 Brier skill score =1 - (Brier score RI index/Brier score climatology) Thus, the RI index has skill (no skill) if it has a Brier score that is less (greater) than climatology (Wilks 1995)

10. Brier Skill scores for the GOES versions of the Atlantic and E. Pacific RI indices for the dependent samples (95-02)

11. Real-time performance of the non-GOES and GOES versions of the Atlantic RI index (2001-2003) Non-GOES GOES

12. Brier Skill scores of the real-time Atlantic RI index forecasts

13. Performance of the non-GOES version of the E. Pacific RI index for the 2003 re-run forecasts Non-GOES GOES

14. Brier skill scores for the EPAC RI index for the 2003 re-run forecasts

15. Change in 2003 SHIPS model skill obtained by replacing Reynolds SSTs with AMSR-E SSTs (Gentemann 2004) E. Pacific Atlantic

16. Yearly Brier skill scores for the GOES version of the EPAC RI index for the 1995-2002 dependent sample

17. Performance of the GOES version of the scaled RI index for the 1995-2002 E. Pacific dependent sample (N=1248)

18. Summary The Atlantic RI index showed some skill when run in real-time in 2001 and 2003 (GOES version only), but performed poorly in 2002 The GOES version of the RI index was found to be more skillful than the non-GOES version in both basins The E. Pacific version of the RI index showed more skill than the Atlantic version for the dependent samples The 2003 EPAC re-run forecasts were much less skillful than climatology, but appear to be within the range of skill that can be expected in any given year The E. Pacific RI index will be tested in real-time for the first time during the upcoming 2004 Hurricane season The possibility of developing a scaled version of the E. Pacific RI index is also being investigated

19. 24-h mean intensity changes for the non-GOES and GOES versions of the Atlantic RI index (2001-2003) Non-GOESGOES

20. 24-h mean intensity changes for the E. Pacific 2003 re-run forecasts Non-GOESGOES