1. Reasons for the Unusually Destructive 2004 Atlantic Basin Hurricane Season Phil Klotzbach and William Gray Department of Atmospheric Science Colorado State University Climate Diagnostics Workshop October 25, 2005

2. Outline 2004 Atlantic Hurricane Summary Activity-Enhancing Features Westward Track-Enhancing Features Conclusions

3. Outline 2004 Atlantic Hurricane Summary Activity-Enhancing Features Westward Track-Enhancing Features Conclusions

4. Forecast Parameter and 1950-2000 Climatology (in parentheses) Observed Activity Named Storms (NS) (9.6)14 Named Storm Days (NSD) (49.1)90 Hurricanes (H) (5.9)9 Hurricane Days (HD) (24.5)46 Intense Hurricanes (IH) (2.3)6 Intense Hurricane Days (IHD) (5.0)22 Net Tropical Cyclone Activity (NTC) (100%) 229 2004 ATLANTIC BASIN TROPICAL CYCLONE ACTIVITY

5. 2005 Season

6. Figure taken from http://www.nhc.noaa.gov/tracks/2004atl.gif

7. Figure taken from http://www.wunderground.com/hurricane/at2005.asp

8. 9 Landfalls

9. 2004 United States Hurricane Landfalls NameDateLandfall Location Landfall Intensity (kts) Insured Damage (Millions) Charley – Landfall 1 8/13Cayo Costa, FL 130$7000 Charley – Landfall 2 8/14Cape Romain, SC 70$50 Frances9/5Hutchinson Island, FL 90$4500 Gaston8/29Awendaw, SC 65$65 Ivan9/16Gulf Shores, AL 105$7000 Jeanne9/26Hutchinson Island, FL 105$3500

10. Outline 2004 Atlantic Basin Statistics Activity-Enhancing Features Westward Track-Enhancing Features Conclusions

11. August-September 2004 SST Anomalies

12. 1860 1900 1940 1980 2020 Adapted from Goldenberg et al. 2001

13. August-September 2004 850 MB U Anomaly

14. August-September 2004 V Anomalies 200 mb 850 mb Anomalous Northerlies Anomalous Southerlies

15. August-September 2004 OLR Anomaly

17. Genesis Parameter (GP) Definition GP = ΔV + U 850mb + SSTA Where: ΔV = 850 mb – 200 mb average August- September V wind component from (7.5°N – 7.5°S, 20°-45°W) U 850mb = 850 mb average August-September U wind component from (5°-15°N, 20°-60°W) SSTA = Average August-September sea surface temperature anomaly from (5°-15°N, 20°-60°W)

18. SSTA + U V 1.5 km 12 km Genesis Parameter (GP) Component Locations

19. Genesis Parameter Values (in Standard Deviations) PeriodΔVΔVU 850mb SSTGenesis Parameter Aug-Sep Named Storm Formations South of 25°N 1950-1969-0.10.80.00.34.7 1970-1994-0.4-0.8-0.4-0.73.3 1995-20031.20.40.91.25.4 20042.3 (2)0.5 (17)1.8 (3)2.2 (2)9 (T-1)

20. Atlantic Basin Genesis Parameter Ratios RatioNamed Storm Formations south of 25°N Ratio Highest 5 / Lowest 533 / 14 (2.4:1) Highest 10 / Lowest 1058 / 21 (2.8:1) Highest 25 / Lowest 25132 / 77 (1.7:1)

21. August-September SST (1995-2004) – (1950-1969)

22. August-September 200 mb U (1995-2004) – (1950-1969)

23. Upper-Level Wind Parameter (UP) Definition UP = -ZWA Where: ZWA = 200 mb average August-September U wind component from (5°-15°N, 20°-60°W)

24. - ZWA 12 km Upper-Level Wind Parameter (UP) Location

25. Upper-Level Wind Parameter Values (in Standard Deviations) PeriodUP 1950-19690.5 1970-1994-0.3 1995-2003-0.3 2004-0.2

26. Outline 2004 Atlantic Basin Statistics Activity-Enhancing Features Westward Track-Enhancing Features Conclusions

27. 1995-2003 Intense Hurricane Tracks (32 tracks) FRAN OPAL BRET

28. August-September 500 mb Ht. (2004) – (1995-2003)

30. Westward Track Parameter (WP) Definition WP = Zone 1 – Zone 2 – Zone 3 Where: Zone 1 = 500 mb average August-September 500 mb height from (40°-50°N, 65°-75°W) Zone 2 = 500 mb average August-September 500 mb height from (50°-60°N, 20°-30°W) Zone 3 = 500 mb average August-September 500 mb height from (40°-50°N, 100°-110°W)

31. L LH

32. United States Tropical Cyclone Landfall Parameter (LP) Definition LP = GP + UP + WP Where: GP = Genesis Parameter UP = Upper-Level Wind Parameter WP = Westward Track Parameter

33. United States Landfall Parameter (LP) Values (in Standard Deviations) PeriodGP (Genesis) UP (Upper-Level Winds) WP (Track) LP (Landfall) Aug-Sep US Hurricane Landfalls 1950-19690.30.50.00.51.4 1970-1994-0.7-0.30.0-0.71.0 1995-20031.2-0.3-0.10.51.0 20042.2 (2)-0.2 (31)1.1 (5)2.0 (2)6 (1)

34. United States Landfall Parameter Ratios RatioNamed Storm Ratio Hurricane Ratio Intense Hurricane Ratio Highest 5 / Lowest 5 21 / 7 (3:1) 13 / 3 (4.3:1) 7 / 2 (3.5:1) Highest 10 / Lowest 10 32 / 12 (2.7:1) 19 / 4 (4.8:1) 11 / 2 (5.5:1) Highest 25 / Lowest 25 64 / 43 (1.5:1) 37 / 23 (1.6:1) 22 / 9 (2.4:1)

35. Outline 2004 Atlantic Basin Statistics Activity-Enhancing Features Westward Track-Enhancing Features Conclusions

36. The 2004 hurricane season was very active both in terms of overall tropical cyclone activity and in terms of United States landfalls A strong Intertropical Convergence Zone, weaker trade winds, and warm Atlantic sea surface temperatures contributed to the very active season A mid-level ridge predominated over the East Coast of the United States with mid-level troughs to the west and east which helped push storms westward into the longitudes of the United States