1. 2003 Atlantic Hurricane Season Summary By Gerald Bell, Muthuvel Chelliah Climate Prediction Center NOAA/ NWS And NOAA Atlantic Hurricane forecast team members Dr. Chris Landsea 1, Stanley Goldenberg 1, Dr. Richard Pasch 2, Eric Blake 2 1 Hurricane Research Division/ NOAA/ OAR 2 National Hurricane Center/ NOAA/ NWS

2. Outline 1.Season statistics 2.Total seasonal activity 3.Rainfall from U.S. landfalling tropical systems 4.Atmospheric circulation 5.Ongoing active decadal signal 6.NOAA Atlantic Hurricane Outlooks 7.Summary

3. 2003 Atlantic Hurricane Season Statistics Observed Above Normal 14 Tropical Storms 6 Hurricanes 3 Major Hurricanes 180.5 % ACE Index (% median) Observed NOAA Prediction Season Type May 23 August 7 Above Normal Above Normal 55% 60% Near Normal 35% 35% Below Normal 10 % 5% 14 Tropical Storms 11-15 12-15 6 Hurricanes 6-9 7-9 3 Major Hurricanes 2-4 3-4 183 % ACE Index (% median) 110-180% 120-170%

4. Main Development Region (MDR) Main Development Region MDR is defined as tropical Atlantic and Caribbean Sea between 9 o -21.5 o N During 1949-2002 Tropical Systems first named in MDR account for: 71% of the 53-year total activity measured by ACE index 55% of all hurricanes 79% of all major hurricanes Nine-fold drop in activity in MDR between above- and below-normal seasons

5. 2003 Named Storm Tracks Figure Courtesy of Unisys.com Main Development Region

6. 2003 Atlantic Tropical Systems By Region Where First Named All Main Development Region Extratropics Gulf of Mexico Tropical Hurricanes Major Storms Hurricanes

7. Total Seasonal Activity Total seasonal activity: Collective strength and duration of tropical storms and hurricanes More representative of overall activity than seasonal numbers systems NOAA’s Accumulated Cyclone Energy (ACE) Index: Wind energy index defined as sum of squares of 6-hourly maximum sustained wind speed for all systems while at least tropical storm strength. Similar to HDP index ( Gray et al., CSU). ACE is highly predictable and dominated by activity in MDR Key forecast parameter for NOAA hurricane outlooks Used to classify seasons: above normal, near normal, below normal

8. Active Decades ACE = 114 10 TS, 6.5 H, 3 MH Above Normal Season Near Normal Below Normal Season 65 103 2003 Historical Perspective: ACE Index Atlantic Basin Main Development Region Active Decade ACE = 134 13 TS, 8 h, 3.6 MH IN-active Decades ACE = 65 9 TS, 5 H, 1.5 MH 2003 Predicted Range

9. 2003 ACE Index for storms first named in specified region

10. 2003 ACE Index by Storm Main Development Region Extratropics Gulf of Mexico

11. U.S. Rainfall Totals Landfalling Tropical Systems 6 named storms made landfall in U.S. during 2003 4 formed over Gulf of Mexico 2 formed in MDR 1 hit as tropical depression (Henri) 3 hit as tropical storms (Bill, Grace, Erika) 2 hit as hurricanes (Claudette, Isabel)

12. Storm Precipitation Totals (mm) TS Bill (G. Mexico) 30 Jun - 1 Jul Hurricane Claudette (MDR) 15-16 July

13. Storm Precipitation Totals (mm) TS Grace (G. Mexico) 31 August TS Erika (G. Mexico) 16-17 August

14. Storm Precipitation Totals (mm) TS Henri (G. Mexico) 6 Sep Hurricane Isabel (MDR) 18-19 Sep

15. Precipitation (mm): 30 Jun – 9 Oct Total Precipitation during landfall days Percent of Period Total Precip by landfall days

16. 2003 Aug-Sep Mean Atmospheric Conditions

17. Atlantic Weekly SST Departures ( o C)

18. Height and Anomalies (shading) August-September 200-hPa 1000-hPa Lower Surface Pressure Stronger Subtropical Ridge

19. 200-850 hPa Anomalous Vertical Wind Shear August-September 2003 Lower Shear Anomalous Shear of Zonal Wind Anomalous Strength of Vertical Shear Anomalous Easterly Shear, Stronger Tropical Easterly Jet

20. 700-hPa Rel. Vort. (shading), Zonal Wind (contour) African Easterly Jet axis north of normal Cyclonic Shear (shading) Cyclonic Anoms (Red) Westerly Anoms Anomaly Aug-Sep 2003 Mean

21. Ongoing Decadal Signal

22. 200-850 hPa Anomalous Vertical Shear of Zonal Wind: Aug-Sep. Lower Shear Higher Shear Averaging Region 1980 1985 1990 1995 2000 M/S -8 –6 –4 -2 0 2 4

23. 700-hPa Zonal Wind Anomalies Aug-Sep 1980 1985 1990 1995 2000 Averaging Region M/S –2 –1 0 1 2 3 4

24. Anomalous 700-hPa Relative Vorticity: Equatorward flank of African Easterly Jet Aug-Sep Anticyclonic Cyclonic 1980 1985 1990 1995 2000 x 10 -6 S -1 -4 –2 0 2 4 6 8 Averaging Region

25. NOAA Atlantic Hurricane Outlooks

26. Climate Links to Tropics Tropical convection is dominant forcing of coherent circulation anomalies associated with seasonal and decadal extremes in Atlantic hurricane activity. (Bell and Chelliah 2004) Dominant Climate factors: ENSO (Gray (1984): Tropical multi-decadal mode (TMM): Chelliah and Bell (2003)

27. 1.Predict ASO state of the two leading tropical modes. Use EOF regressions and analogue/ binning techniques to predict upcoming atmospheric conditions and activity in MDR Analysis of the combined modes is critical to the forecast 2. Observed Apr-May, Jun-Jul anomalies to predict ASO activity Analogue years, bin with respect to leading tropical modes. Extended CCA forecasts of vertical shear Final outlook is subjective blend of items 1-2 NOAA’s Atlantic Hurricane Outlooks Forecast Procedure

28. NOAA Seasonal Atlantic Hurricane Outlook August Forecast vs. Observed: 1998-2003 Forecast Range Observed Green bars indicate climatological mean and ACE range for near-normal season (76%-120% of Median) Tropical Storms ACE Index Hurricanes Major Hurricanes 14 12 15 12 14 135 206 76 122 240 8 8 9 4 10 3 5 4 2 3 14 6 3 183

29. Summary 1.Above-normal 2003 Atlantic hurricane season. 2.1995-2003 most active in record 2. Most of 2003 activity (86% of ACE index) associated with MDR. 3. Ongoing decadal atmospheric signal favors active hurricane seasons. 4. NOAA outlooks based on prediction of ENSO and Tropical Multi-decadal Mode 5. Diagnosing and forecasting seasonal Atlantic hurricane variability requires an understanding of both modes, and their combined impacts.

30. Enhanced Tropical Easterly Jet (200-mb) 2003 Above-normal Hurricane Season Conditions Favorable African Easterly Jet (700-hPa) reflects Northward shift of jet axis Strong cyclonic shear along southern flank Very Low Vertical Shear 850-mb Westerlies (Weaker Easterly Trades) Favorable African Easterly Jet (700-hPa) Amplified Subtropical Ridge Much activity in MDR Stronger Tropical Easterly Jet (200- hPa) WET

31. Extras

32. 700-hPa Rel. Vort., Zonal Wind (contour) Cyclonic Westerly April-May 2003 Anomalies June-July 2003 Anomalies

33. 700-hPa Potential Vorticity August-September Mean 2003 1997 (Inactive Season) High PV in MDR, Gradient Reversal Linear Instability Lower PV in MDR, No Gradient Reversal

34. Precipitable Water (inches), 1000-hPa Wind August-September 2003 High Precipitable water in MDR and West African monsoon region