How Well Forecast Were the 2004 and 2005 Atlantic and U.S. Hurricane Seasons?

1. How Well Forecast Were the 2004 and 2005 Atlantic and U.S. Hurricane Seasons? Mark Saunders and Adam Lea Department of Space and Climate Physics Benfield Hazard Research Centre University College London Royal Meteorological Society Meeting Hurricanes 15th March 2006

2. 2004/5 Hurricane Seasons • Rank as the most active and damaging consecutive hurricane years on record. • Seven intense hurricane landfalls on the U.S. (norm is one). • Estimated total damage bill approaching US $ 200 bn (norm is US $ 10bn). 11:00 UT 29 August 2005 (Courtesy NOAA) RMetSoc Hurricanes March 2006

3. Structure 1. How unusual were 2004 and 2005? 2. Reasons for high Atlantic and U.S. hurricane activity in 2004 and 2005. 3. Seasonal Forecast Comparison (a) Atlantic basin hurricane activity. (b) U.S. landfalling hurricane activity. 4. Forecast Business Application. 5. Conclusions. RMetSoc Hurricanes March 2006

4. 2005 Hurricane Season 1 Most active and damaging on record. Most tropical storms: 27 Most hurricanes: 15 Most Cat 5 hurricanes: 3 Most major hurricanes to strike the U.S.: 4 Highest US hurricane insured damage: ~ US $ 50bn. RMetSoc Hurricanes March 2006

5. Major Gulf Hurricanes in 2004/5 First time since 1915/6 that four major hurricanes have struck the Gulf Coast in two years. RMetSoc Hurricanes March 2006

6. Florida Damaging Storms 2004 First time since 1886 that four hurricanes have struck the same state in one year. RMetSoc Hurricanes March 2006 Courtesy of NOAA and UW-CIMSS

7. Most Costly US Insured Losses RMetSoc Hurricanes March 2006

8. 2. Reasons for high Atlantic and U.S. hurricane activity in 2004 and 2005 RMetSoc Hurricanes March 2006

9. August/September 2004/5 Sea Surface Temperature Anomaly (1950-2003 average) +0.67°C SST anomaly in hurricane main development region RMetSoc Hurricanes March 2006

10. August/September 2004/5 Anomaly in Vertical Wind Shear (1995-2003 average) RMetSoc Hurricanes March 2006

11. August/September 2004/5 Mean Sea Level Pressure Anomaly (1995-2003 average) RMetSoc Hurricanes March 2006

12. August/September 2004/5 925-400mb Height Averaged Wind Anomalies (1995-2003 average) Steering winds on-shore RMetSoc Hurricanes March 2006

13. 3. Seasonal Forecast Comparison RMetSoc Hurricanes March 2006

14. Organisations Providing Seasonal Forecasts Seasonal Atlantic hurricane forecasts for the 2004 and 2005 seasons were issued by: Tropical Storm Risk (TSR) (9 for each season) Gray/Colorado State University (6 for each season) NOAA (2 for each season) Meteorological Institute, Cuba (2 for each season) RMetSoc Hurricanes March 2006

15. U.S. ACE Index The U.S. ACE (Accumulated Cyclone Energy) Index: • Combines storm numbers, intensity and duration within a single index (Saunders and Lea, 2005). • Defined as the sum ofthe squares of hourly maximum 1-min sustained winds for all storm systems over the U.S. mainland while they are at least tropical storm in strength. • Strongly linked to U.S. hurricane insured loss(Collins and Lowe, 2001) with a rank correlation of 0.7 for the period 1900-2005. RMetSoc Hurricanes March 2006

16. Deterministic Forecasts for 2005 RMetSoc Hurricanes March 2006

17. Deterministic Forecasts for 2005 5.5 RMetSoc Hurricanes March 2006

18. Probabilistic Forecasts for 2005 North Atlantic ACE Index RMetSoc Hurricanes March 2006

19. Probabilistic Forecasts for 2005 U.S. ACE Index RMetSoc Hurricanes March 2006

20. Probabilistic Forecasts for 2004 North Atlantic ACE Index RMetSoc Hurricanes March 2006

21. Probabilistic Forecasts for 2004 U.S. ACE Index RMetSoc Hurricanes March 2006

22. U.S. Hurricane Prediction Model Saunders, M. A. and A. S. Lea, Seasonal prediction of hurricane activity reaching the coast of the United States, Nature, 434, 1005-1008, 2005. • First example of useful skill for predicting seasonal US landfalling hurricane activity and damage. • The model has a sound physical basis. • The model will benefit risk awareness and offers good potential for application in business decision making. RMetSoc Hurricanes March 2006

23. 4. Forecast Business Application RMetSoc Hurricanes March 2006

24. Background • The TSR early August forecast model (Saunders and Lea, 2005) correctly anticipates whether U.S. hurricane losses are above-median or below-median in 74% of years between 1950 and 2003. • This skill combined with the success of the seasonal U.S. landfalling hurricane forecasts for 2004 and 2005, suggests that forecast precision may now be high enough to offer potential benefit to industries whose returns are affected by hurricane damage. RMetSoc Hurricanes March 2006

25. Hurricane Loss Probability US hurricane total insured loss contingent on the TSR (Tropical Storm Risk) 1st August forecast. The chance of a large total loss is much higher in those years when the forecast is high. RMetSoc Hurricanes March 2006

26. 2004 and 2005 • For the damaging 2004 and 2005 hurricane seasons the TSR early August forecasts predicted U.S. landfalling hurricane activity in the upper quartile and upper decile respectively. • Thus TSR would have recommended that insurance companies purchase extra protection. RMetSoc Hurricanes March 2006

27. 5. Conclusions • 2004 and 2005 Atlantic and U.S. landfalling hurricane seasons were both predicted to be active (upper tercile activity to high probability) from the previous December. • Overall the TSR forecasts slightly outperformed those from the other forecast groups (certainly the case for U.S. landfalling activity). • Seasonal forecast precision now appears high enough to be practically useful. RMetSoc Hurricanes March 2006