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Development of a Rapid Intensification Index for the Eastern Pacific Basin

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. March 9, 2005. Acknowledgements: Joint Hurricane Testbed. Background.

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Development of a Rapid Intensification Index for the Eastern Pacific Basin

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  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 March 9, 2005 Acknowledgements: Joint Hurricane Testbed

  2. Background • The present operational hurricane intensity prediction models have not demonstrated the capability to predict rapid intensification (RI) adequately and predicting RI has been ranked as one of the top forecasting priorities by the NHC • Kaplan and DeMaria (2003) developed a simple index for predicting the probability of RI in the Atlantic basin using SHIPS model output • The Atlantic RI index was tested in real-time from 2001-2003 as part of the Joint Hurricane Testbed (JHT) and was run operationally during the 2004 hurricane season • An RI index analogous to the one developed for the Atlantic basin is also currently being developed for the E. Pacific basin with support from the JHT

  3. 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) for the Atlantic Basin • This equates to a 24-h maximum sustained wind increase of > 18.0 ms-1 (35 kt) for the E. Pacific Basin

  4. SHIPS predictors used in the Atlantic and E. Pacific versions of the RI index Non-GOES Version(1989-2003) • 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 (24 h mean) • 850-700 hPa relative humidity from 200-800 km (24 h mean) GOES Version(1995-2003) • 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) Threshold methodology: Sea-surface temperature threshold(°C): 28.8 Observed sea-surface temperature(°C): 28.7 Sea-surface temperature threshold not satisfied

  5. Brier skill of the 2003 Atlantic basin RI index real-time forecasts

  6. Brier skill of the 2003 E. Pacific RI index independent (re-run) forecasts

  7. Darby (2004)

  8. Frank (2004)

  9. Howard (2004)

  10. Javier (2004)

  11. Brier skill of the 2004 real-time E. Pacific RI index forecasts

  12. Scaled RI index Methodology: Similar in concept to that used by DeMaria et al. (2001) for genesis forecasting Np Scaled RI index = 10*{ ∑ S } i=1 Where: Np is the number of RI predictors ( 7 are used) Sis the scaled magnitude (from 0 to 1) of each predictor (S=1when the predictor value is most conducive for RI and S= 0 when it is the least conducive).

  13. Brier skill of the threshold and scaled versions of the RI index for the 1995-2003 Atlantic (N=1733) and E. Pacific (N=1446) developmental samples

  14. Howard 2004 (independent)

  15. Brier skill of the 2004 Atlantic (N=294) and E. Pacific (N=181) independent (re-run) forecasts

  16. Brier skill of the scaled version of the RI index for the developmental (1995-2003) Atlantic and E. Pacific samples for the 20, 25, 30 and 35 kt RI thresholds

  17. Brier skill of the 2004 independent (re-run) Atlantic and E. Pacific forecasts for the scaled version of the RI index for the 20, 25, 30, and 35 kt RI thresholds

  18. Howard (2004) (independent)

  19. Summary • The 2004 real-time version of the E. Pacific RI index showed skill • relative to climatology. • A new scaled version of the RI index was developed and tested • against the previously developed threshold version. The tests • showed that scaled version was significantly more skillful than the • threshold version in the E. Pacific basin but only slightly more skillful in the Atlantic when evaluated using the 1995-2003 developmental sample. • For the 2004 independent re-run forecasts, the scaled version outperformed the threshold version by 7 to 10 % for the Atlantic and E. Pacific basins respectively. • An evaluation of the scaled version of the RI index for various RI • thresholds showed a significant increase in skill for lower RI thresholds. • This results suggests that it might be prudent to either use a slightly • lower RI threshold or to add a second RI threshold with a smaller • magnitude.

  20. Brier skill of the 2004 Atlantic basin operational forecasts

  21. Charlie (2004)

  22. Brier skill score N Brier Score = 1/N ∑ (F-E)2 (Wilks 1995) i=1 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) Brier skill score =1 - (Brier score RI index/Brier score climatology) Thus, the RI index had skill (no skill) if it had a Brier score that was less (greater) than climatology

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