1. INNER CORE STRUCTURE AND INTENSITY CHANGE IN HURRICANE ISABEL (2003) Shuyi S. Chen and Peter J. Kozich RSMAS/University of Miami J. Gamache, P. Dodge, F. Marks NOAA/AOML/HRD 27 th AMS Tropical & Hurricane Conference, April 23-28, 2006, Monterey, CA.

2. 12-14 Sept 2003 LF Radar Reflectivity (dBZ) Composite from NOAA-42 RF http://www.aoml.noaa.gov/hrd/Storm_pages/isabel2003/radar.html 9/12 1644-1709 UTC9/13 1625-1650 UTC9/14 1822-1852 UTC 9/12 2000-2030 UTC9/13 1915-1945 UTC9/14 2157-2222 UTC

3. http://www5.ncdc.noaa.gov/cgi-bin/hsei/hsei.pl

4. What has been observed in Isabel? significant inner core structure changes concentric eyewalls mesovortices in the eye What role do they play in Isabel’s intensity and intensity change?

5. Model and Data PSU-NCAR MM5 (nested domains with 45,15,5, and 1.67 km grid resolution, 28 sigma levels, Chen and Tenerelli 2006) NCEP global analysis fields as initial and lateral B.C. Vortex relocation scheme (Liu et al 1997) NOAA/HRD airborne Doppler radar, flight-level, and GPS dropsonde data 45km 1.6 5 15

6. Isabel Tracks, from Best Track and MM5 Investigation focuses on time frame between arrows; observation and model times are different

7. Intensity (minimum SLP) Investigation focuses on time frame between arrows

8. Idealized barotropic model (Schubert et al. 1999, Kossin et al. 2000) (Kossin et al. 2000) Evolution of a single primary eyewall Evolution of primary + secondary eyewalls

10. Hovmoller Diagrams of Azimuthal Averaged MM5 Rainrate and Tangential Windspeed at 2km Level 14 th 13 th 12 th

11. 9/12 9/13 9/14 Radar MM5 Observed and Model Simulated Tangential Wind Speed (ms -1 ) at 1-km level

12. 9/12 913 914 Azimuthally Averaged Reflectivity Radar MM5

13. Flight Level Wind (Blue) and MM5 Wind (Red) at 2km level 9/12 913 914 mean

14. 9/12 9/13 9/14 Radar MM5 Relative Vorticity (x 10 -3 s -1 ) at 1-km level

15. Potential Vorticity at 1-km Level 0600 Z 9/11 1200 Z 1800 Z 0000Z 9/12 0600 Z 1200 Z 1800 Z 0000Z 9/13 0600 Z 1200 Z 1800 Z 0000Z 9/14

16. Inertial Stability Analysis Hack and Schubert (1986): IS = [(f + 2V/r)(f +  )] 1/2 = [(f + 2V/r)(f + V/r +  V /  r)] 1/2

17. Intensifying storm Highest flight-level winds with a sharp bell-shaped profile High inertial stability (IS) inside of the eyewall Strong eyewall updrafts and convection Secondary wind max 9/12/03 IS V(r) RMW

18. 9/13/03 Eyewall replacement Less sharp bell-shaped wind profile Lowered inertial stability (IS) inside of the eyewall Weakened eyewall updrafts and convection RMW

19. 9/14/03 Weakened storm Linear-shaped wind profile Lower inertial stability (IS) Weak and broad eyewall updrafts and convection RMW

20. MM5 T (color - upper panels), T d (contour) and  e (color - lower panels) 9/12 913 914 Mixing of the eye and eyewall

21. Conclusions Intensification is associated with storm’s ability to maintain strong eyewall convection, sharp bell- shaped wind profile and high inertial stability inside of the eyewall (i.e., eyewall contraction). Formation of secondary eyewall and eyewall replacement weaken the convection in the primary eyewall. Mixing of the eye and eyewall by vortex Rossby waves (mesovorties) contributed to the collapse of the inner eyewall and weakening of Isabel (before the vertical wind shear increased on 9/15/03).