Performance of the SHIPS Rapid Intensification Index for the 2002 Atlantic Hurricane Season

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Performance of the SHIPS Rapid Intensification
Index for the 2002 Atlantic Hurricane Season

• John Kaplan
• Hurricane Research Division/AOML
• Miami, FL
• Mark DeMaria
• NOAA/NESDIS
• Fort Collins, CO
• Acknowledgments Joint Hurricane Testbed (JHT)

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Definition of Rapid Intensification (RI)

• Rapid intensification (RI) is defined as the 95th
  percentile of the over-water 24-h intensity
  changes of all tropical depressions, tropical
  storms, and hurricanes that developed in the
  Atlantic basin from 1989-2000
• This equates to a 24-h maximum sustained wind
  increase of gt 15.4 ms-1 (30 kt)

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Development of the SHIPS RI index (Kaplan and
DeMaria 2002)

• 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 t0 h SHIPS predictor magnitudes
  to the corresponding RI thresholds
• Employ the 5 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 Atlantic basin SHIPS forecast

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Predictors used in the Rapid intensification (RI)
index

• Previous 12 h intensity change
• Observed sea-surface temperature at t0 h
• Maximum potential intensity - initial storm
  intensity at t0 h
• 850-200 hPa vertical shear from 200-800 km at t0
  h
• 850-700 hPa relative humidity from 200-800 km at
  t0 h

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RI index changes for 2002 season

• RI index re-derived using updated dependent
  sample which included
• Cases from 2001 season
• Entire life-cycle of all tropical cyclones
  (non-tropical low and wave stages included)
• RI thresholds were determined by averaging the
  magnitudes of all predictors from t0 h to t24 h
  (except previous 12-h intensity change)
• Revised RI probabilities were determined using
  the new RI thresholds described above
• Updated RI index was installed on 16 July 2002

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Development of an updated RI index

• Dataset A
• 553 cases from 1995-2001 (west of 50 ºW)
• Cases were comprised of tropical depressions,
  tropical storms, and hurricanes
• Standard RI predictors as well as ocean heat
  content (Mainelli et al. 2002) and GOES IR data
  (Zehr 2000)
• Dataset B
• 1235 cases from 1995-2001
• Cases were comprised of tropical depressions,
  tropical storms, and hurricanes
• Standard RI predictors and GOES IR data (Zehr
  2000)

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Predictors used in the GOES version of the Rapid
intensification (RI) index

• Previous 12 h intensity change
• Observed sea-surface temperature at t0 h
• Maximum potential intensity - initial storm
  intensity at t0 h
• 850-200 hPa vertical shear from 200-800 km at t0
  h
• 850-700 hPa relative humidity from 200-800 km at
  t0 h
• Standard deviation of the brightness temperature
  from
• 50-200 km
• Percent area covered by -50 ºC from 50-200 km

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Summary

• The SHIPS RI index did not perform as well during
  the the 2002 season as it did during the 2001
  season.
• The addition of GOES information improved the
  performance of the RI index for the (1995-2001)
  dependent sample. However, the independent
  results for the 2002 season were inconclusive.
• The addition of ocean heat content did not
  improve the performance of the RI index for the
  1995-2001 dependent sample. Additional research
  will be required to improve methods of
  incorporating this information.
• Both the standard (5 predictor) and GOES (7
  predictor) versions of the RI index will be run
  in real-time during the 2003 Atlantic hurricane
  season.