Development of a Rapid Intensification Index for the Eastern Pacific Basin

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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
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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

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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

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SHIPS predictors used in the Atlantic and E.
Pacific versions of the RI index
Non-GOES Version (1989-2003)

• Previous 12 h intensity change (t0 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
  (t0 h)
  
• Standard deviation of inner-core brightness
  temperature (t0 h)
  

Threshold methodology Sea-surface temperature t
hreshold(C) 28.8 Observed sea-surface temper
ature(C) 28.7 Sea-surface temperature thresho
ld not satisfied
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Brier skill of the 2003 Atlantic basin RI index
real-time forecasts
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Brier skill of the 2003 E. Pacific RI index
independent (re-run) forecasts
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Darby (2004)
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Frank (2004)
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Howard (2004)
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Javier (2004)
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Brier skill of the 2004 real-time E. Pacific RI
index forecasts
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Scaled RI index
Methodology Similar in concept to that used by
DeMaria et al. (2001) f
or genesis forecasting
Np S
caled RI index 10 ? S
i1
Where Np is the number of RI predictors ( 7 ar
e used) S is the scaled magnitude (from 0 to 1) o
f each predictor (S1 when the predictor value i
s most conducive for RI and S 0 when it is the
least conducive).
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Brier skill of the threshold and scaled versions
of the RI index for the 1995-2003 Atlantic
(N1733) and E. Pacific (N1446) developmental
samples
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Howard 2004 (independent)
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Brier skill of the 2004 Atlantic (N294) and
E. Pacific (N181) independent (re-run)
forecasts
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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
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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
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Howard (2004) (independent)
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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 deve
loped threshold version. The tests
showed that scaled version was significantly more
skillful than the threshold version in the E. Pa
cific 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 signif
icant 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 a
dd a second RI threshold with a smaller
magnitude.
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Brier skill of the 2004 Atlantic basin
operational forecasts
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Charlie (2004)
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Brier skill score
N
Brier Score 1/N ? (F-E)2
(Wilks 1995)
i1
N number of forecasts F forecast probability (
where 50 is expressed as 0.5)
E Event probability (where E1 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 c
limatology