1. Verification of Colorado State University’s Atlantic Basin Seasonal Hurricane Forecasts Phil Klotzbach and William Gray Department of Atmospheric Science Colorado State University Phil Klotzbach and William Gray Department of Atmospheric Science Colorado State University

2. Outline Hindcast Verification Real-Time Forecast Verification Hindcast Verification Real-Time Forecast Verification

3. How do you calculate Net Tropical Cyclone (NTC) Activity? NTC activity in any year consists of the seasonal totals of named storms, named storm days, hurricanes, hurricane days, major hurricanes and major hurricane days in terms of their long-term period averages and multiplied by 100. So, as an example, let’s look at 2005: 2005 NTC Calculation (1950-2000 Climatological Values in Parentheses) Named Storms (9.6)28 Named Storm Days (49.1)131.50 Hurricanes (5.9)15 Hurricane Days (24.5)49.75 Major Hurricanes (2.3)7 Major Hurricane Days (5.0)17.50 Note: Seasonal values are in parentheses Now to calculate NTC, sum the following six ratios: 28/9.6 = 291, 131.50/49.1 = 268, 15/5.9=254, 49.75/24.5 = 203, 7.0/2.3 = 304, 17.5/5.0 = 350 2005 NTC = (291+268+254+203+304+350)/6 = 279

4. Date 7 Dec. 10 Apr. 3 June 2 Aug. SeasonalForecastXXXX 2013 Forecast Schedule 2013 Forecast Schedule

11. % Improvement in Mean Absolute Error (2008-2012) vs. (Beginning of Forecast - 2007) AprilJuneAugust Named Storms10%12% Named Storm Days24%12%11% Hurricanes3%-4%-14% Hurricane Days41%35%20% Major Hurricanes70%75%83% Major Hurricane Days61%46%24% Net Tropical Cyclone Activity54%63%47%

12. Future Work Redevelop April and June statistical forecast models using ERA-Interim data Initiate July seasonal forecast model (Klotzbach 2013, manuscript accepted for publication) Investigate skill of forecast models using longer- period hindcast data, including ESRL’s 20 th Century Reanalysis as well as the ERA-CLIM Reanalysis which should be available by early 2014

13. Arago’s Admonition: “Never, no matter what may be the progress of science, will honest scientific men who have regard for their reputations venture to predict the weather.” Arago’s Admonition: “Never, no matter what may be the progress of science, will honest scientific men who have regard for their reputations venture to predict the weather.”