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3  Winds < 35 kts  Numbered, but not named  Semi-organized group of thunderstorms Lifecycle Ingredients ClimatologyData

4  Winds 35–63 kts  ≈ 11 per year in the Atlantic  Named  More circular/spiral, but no eye Lifecycle Ingredients ClimatologyData

5  Winds ≥ 64 kts  ≈ 6 per year in the Atlantic  Eye develops  Different names around the world:  Hurricane in the Atlantic and East Pacific  Typhoon in West Pacific  Cyclone in Indian Ocean and South Pacific  “Tropical Cyclone” is the generic/scientific term Lifecycle Ingredients ClimatologyData

6  Winds ≥ 96 kts  ≈ 2-3 per year in the Atlantic  Category 3–5 on the Saffir–Simpson Scale  Strong and dangerous storms  Well-defined, circular eye Lifecycle Ingredients ClimatologyData

7  Deep warm ocean layer  Warm oceans are the energy source for hurricanes  But hurricanes can mix cold water upward if the warm water is too shallow  Conditionally unstable atmosphere  Warm air rises, but only if it’s warmer than its surroundings  Moist mid-troposphere  Dry air 2-3 km from the surface can cause cold downdrafts ww2010.atmos.uiuc.edu Lifecycle Ingredients ClimatologyData

8  Pre-existing convection  Needs organized thunderstorms to get things going  Cyclonic low-level vorticity  Counter-clockwise spinning winds help organize the thunderstorms  Associated with low pressure  Weak vertical wind shear  Tilting winds can knock the storm over Lifecycle Ingredients ClimatologyData

9  Wind shear is defined as the wind vector difference between the 850 and 200 mb level (arbitrary) High westerly shearLow easterly shear In general, low values (< 20 kt) of vertical wind shear are desired. Bad – convection torn apart Good – latent heat can concentrate in one area Courtesy of C.C. Hennon, UNC Asheville Lifecycle Ingredients ClimatologyData

10  Thunderstorm systems with wave-like properties  Move westward with a period of 3–6 days  Common over West Africa  Provides storms with cyclonic vorticity and convection Berry et al. (2007, Mon. Wea. Rev.) Lifecycle Ingredients ClimatologyData

11  Warm Ocean Temperatures  Supply of Tropical Waves from Africa  10°N to 20°N  20°W to 60°W or 80°W Lifecycle Ingredients ClimatologyData

12  Dry air from Sahara can weaken storms  Dust blocks the sun and cools the ocean Zipser et al. (2009, BAMS) climate.nasa.gov Lifecycle Ingredients ClimatologyData

13 Knapp et al. (2010, BAMS) Lifecycle Ingredients ClimatologyData

14  Bars depict number of named systems (open/yellow), hurricanes (hatched/green), and category 3 or greater (solid/red), nhc.noaa.gov/climo Lifecycle Ingredients ClimatologyData

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22  Historical record of tropical cyclone locations and intensities  Constructed after each season by the warning agencies  Best estimate using all available data nhc.noaa.gov Lifecycle Ingredients ClimatologyData

23  Weather stations  Buoys  Ships  Radar  Aircraft Reconnaissance  Visible/Infrared Satellites  Microwave satellites  Satellite estimates account for vast majority of the record Courtesy of Jack Beven (NOAA/NHC) Lifecycle Ingredients ClimatologyData

24  Weather stations  Buoys  Ships  Radar  Aircraft Reconnaissance  Visible/Infrared Satellites  Microwave satellites  Satellite estimates account for vast majority of the record Courtesy of Jack Beven (NOAA/NHC) Lifecycle Ingredients ClimatologyData

25 Which image on the right is the closest match for this image of Hurricane Katrina?