© 2006 Accurate Environmental Forecasting Climate Effects on Hurricane Frequency and Severity Dail Rowe, PhD Accurate Environmental Forecating

© 2006 Accurate Environmental Forecasting Overview Clear links between climate and hurricanes –Atlantic Sea-Surface Temperature –El Nino/ENSO –North Atlantic Oscillation The Hurricane Index –Objective, peer-reviewed analysis technique –Performance and validation –Use in hurricane catastrophe risk assessment tools What’s new? –Is their really a cycle in the Atlantic SST anomaly? –Predictions from months to decades –Inclusion of climate forecast uncertainty

© 2006 Accurate Environmental Forecasting Climate Signals – Fundamental Physics Atlantic Sea-Surface Temperature (SST): –Warmer water provides more energy for storms El Niño (ENSO): –Vertical wind-shear, which retards hurricane growth, increases during El Niño and decreases during La Niña North Atlantic Oscillation (NAO): –Correlated with SST changes in the southwestern Atlantic and average steering winds, both of which affect hurricane activity

© 2006 Accurate Environmental Forecasting Relationship Between Wintertime Atlantic SST and Major Hurricanes 9-year running mean SST and hurricane records

© 2006 Accurate Environmental Forecasting Cat 3+ Hurricane Activity and Sea-Surface-Temperature BasinwideUS LandfallsFlorida Landfalls Cold: Cold: Cold Average1.41 / year0.48 / year0.15 / year Warm: Warm: Warm Average2.96 / year0.83 / year0.38 / year

© 2006 Accurate Environmental Forecasting The Impact of ENSO Warm (El –Nino)Cold (La Nina) Basin-wide Hurricanes3860 Basin-wide Major Hurricanes1626 Near-landfall Hurricanes1621 Near-landfall Majors611 Hurricane counts during the 9 strongest El-Nino and La- Nina events since 1950.

© 2006 Accurate Environmental Forecasting What is the Hurricane Index? The hurricane index, as developed by AEF for climate conditioning, is the ratio between expected and average hurricane occurrence rates. Index values are calculated using a Generalized Linear Modeling approach based upon the work of Jim Elsner of Florida State University. Rate in Climate of Interest Average Rate Index =

© 2006 Accurate Environmental Forecasting Generalized Linear Modeling Technique Objective, quantitative statistical analysis informed by physical understanding –Index and uncertainty estimates Peer reviewed Hurricane landfall probability and climate, in Hurricanes and Typhoons: Past, Present, and Future, Columbia University Press, , A hierarchical Bayesian approach to seasonal hurricane modeling, Journal of Climate, v17, , July Examining the ENSO-typhoon hypothesis, Climate Research, v25, 43-54, October Seasonal space-time models for climate systems, Statistical Inference for Stochastic Processes, v6, , 2003.

© 2006 Accurate Environmental Forecasting Forecasting Climate Induced Variability in Hurricane Activity A mix of observed and forecast climate data is used for seasonal predictions –Observed NAO October – February average –Observed SST January – February average –Forecast ENSO August-October ENSO average –Uncertainty in the ENSO forecast is included Forecast SST is used for multi-season predictions –Statistical forecasts including uncertainty

© 2006 Accurate Environmental Forecasting The Hurricane Index: 2005 All HurricanesMajor Hurricanes

© 2006 Accurate Environmental Forecasting Basin-Wide Index Performance The AEF Index analysis technique explains a large percentage of the observed variance in the hurricane record. 35% of the variance in category 1-5 hurricane activity for the period 45% of the variance in category 3-5 hurricane activity for the period

© 2006 Accurate Environmental Forecasting The 2004 and 2005 Hurricane Seasons Charley1.17 Frances1.15 Ivan1.27 Jeanne1.15 Cindy1.49 Dennis1.34 Katrina1.43 Rita1.54 Wilma1.21 Forecast Index values for the landfall locations of 2004 and 2005 storms f 4 major hurricane landfalls during the last 100 years made landfall in regions of elevated risk

© 2006 Accurate Environmental Forecasting Seasonal Outlook: Refining the 5- Year View 5-Year projections are based on SST alone. Seasonal forecasts include analysis of ENSO and NAO. 5-YearEl-Nino and High NAO La-Nina and Low NAO

© 2006 Accurate Environmental Forecasting Integrating the Hurricane Index into Hurricane Event Sets Hurricane Indices are computed in pre-selected regions along the US coast. The Index data are used to construct regional climate conditioned wind-hazard exceedance curves. The frequency and severity characteristics of the tropical cyclone event set are modified to be consistent with the new wind-hazard exceedance curves. Log (return period) Wind Speed Long-run Average Climate Conditioned

© 2006 Accurate Environmental Forecasting The Hurricane Index is integrated into AIR’s Catrader and Classic 2 Products Seasonal catalogs released in May 2005 and 2006 Near-term (5-year) catalog released May 2006

© 2006 Accurate Environmental Forecasting Summary Hurricane frequency and severity are modulated by climate –Atlantic Sea-Surface-Temperature –El-Nino and La-Nina –North Atlantic Oscillation AEF uses a peer-reviewed Generalized-Linear-Modeling approach to quantify the relationship between climate variability and hurricane activity. –Seasonal and multi-season risk assessment –Accounts for uncertainty in the climate forecasts Climate information can be used to modify the frequency and severity of hurricanes in the event sets that are used for modeling hurricane catastrophe risk.