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SEASONAL PREDICTION OF HURRICANE ACTIVITY REACHING THE COAST OF THE UNITED STATES

SEASONAL PREDICTION OF HURRICANE ACTIVITY REACHING THE COAST OF THE UNITED STATES. Mark Saunders and Adam Lea Department of Space and Climate Physics University College London. RMS Conference 2005 Exeter University 16 September 2005. Tropical Storm Risk (TSR).

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SEASONAL PREDICTION OF HURRICANE ACTIVITY REACHING THE COAST OF THE UNITED STATES

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  1. SEASONAL PREDICTION OF HURRICANE ACTIVITY REACHING THE COAST OF THE UNITED STATES Mark Saunders and Adam Lea Department of Space and Climate Physics University College London RMS Conference 2005 Exeter University 16 September 2005

  2. Tropical Storm Risk (TSR) • Founded in 2000, Tropical Storm Risk (TSR) offers a leading resource for forecasting the risk from tropical storms worldwide. • The current TSR consortium comprises experts on insurance, risk management and seasonal climate forecasting. Industry partners: Benfield, Royal &SunAlliance, Crawford & Company. Scientific partner: UCL/Benfieldhrc.

  3. US Hurricane Impacts Hurricane Katrina 11:00 UT 29 August 2005 (Courtesy NOAA) Annual total (economic) and insured losses 1950-2004 from hurricanes striking the U.S. are estimated to be US $ 5.6 bn and US $ 3.0 bn respectively at 2004 prices and exposures.

  4. Seasonal Forecast Relevance • Strong correlation link (0.68; 1900-2004) exists between U.S. hurricane activity and loss. • Skillful seasonal forecasts of U.S. landfalling hurricane activity would benefit society, business and government by reducing risk, uncertainty and financial volatility. • However, significant seasonal U.S. landfalling skill has not been shown to date.

  5. What We Have Done • We show that seasonal US landfalling hurricane wind energy 1950-2003 is predictable from the 1 August start of the main Atlantic hurricane season withuseful and significant (rrank = 0.67; p < 0.001) skill. • Predictability arises from tropospheric height-averaged wind anomalies present over the North Atlantic, North America and east Pacific during July which establishes persistent steering winds that either favour or hinder US hurricane landfall. • Hindcasts are linked significantly (rrank = 0.48; p < 0.01) to U.S. hurricane economic and insured losses 1950-2003.

  6. Monthly Distribution of U.S. Hurricane Strikes 97% of intense (Cat 3 to 5) hurricane strikes on the U.S. and 87% of hurricane hits on the U.S. occur after 1 August. (1950-2004 Data)

  7. Data • Use the NOAA Accumulated Cyclone Energy (ACE) index as our measure of landfalling hurricane wind energy and define this as the US ACE index. • U.S. National Hurricane Center’s North Atlantic hurricane database. • Monthly gridded wind data averaged between 925 and 400 mb from the NCEP/NCAR global reanalysis project 1950-2003. • U.S. hurricane economic and insured loss data are obtained from Pielke and Landsea (1998) and from Collins and Lowe (2000) respectively.

  8. Height-Averaged Winds and US ACE Index Figure shows height-averaged wind anomalies in (a) July and (b) August-September-October linked significantly to years of above-median US ACE index 1950-2003.

  9. Hindcast Skill for US ACE Index Comparison of strength, significance and stationarity in skill from three models. Hindcast skill is significant to p = 0.001 over each of the sub-periods 1950-1976 and 1977-2003.

  10. Hindcast Skill Comparison Hindcast skill from the July wind model is double that possible from knowing the observed North Atlantic total ACE index at the hurricane season end on 30th November.

  11. Hindcast Link to Losses (1) Link between hindcast US ACE index and U.S. hurricane economic and insured losses 1950-2003.

  12. Real-Time Performance The July 925-400mb wind index model performed well in real-time operation in 2004 and 2005. 2004 • US ACE Index forecast (4th August, 2004) to be in upper quartile. • US hurricane losses estimated to be US $ 45 bn (economic) and US $ 23 bn (insured). 2005 • US ACE Index forecast (5th August, 2005) to be in upper decile. • Insured losses from hurricane Katrina estimated to be US $ 40bn to US $ 60bn.

  13. Business Application US hurricane total insured loss contingent on the TSR 1st August forecast. The chance of a large total loss is much higher in those years when the forecast is high.

  14. Summary • To our knowledge this is the 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. Further Information: Saunders, M. A. and A. S. Lea, Seasonal prediction of hurricane activity reaching the coast of the United States, Nature, 434, 1005-1008, 2005.

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