1. Introduction to Hurricane Forecasting John P. Cangialosi Hurricane Specialist National Hurricane Center HSS Webinar 13 March 2012 John P. Cangialosi Hurricane Specialist National Hurricane Center HSS Webinar 13 March 2012

2. NHC Six-Hour Forecast Cycle

3. Visible image Microwave image Reconnaissance data Radar loop Hurricane specialist collect and analyze available observations

4. Receive satellite fix data Hurricane specialist receives estimates of location and intensity via satellite imagery from 2 different agencies þ Determine the center location  Determine the intensity/wind speed  Determine various wind radii  34-, 50-, and 64-kt (when applicable)  Determine various wind radii  34-, 50-, and 64-kt (when applicable) ë Determine past motion (6-12 h)

5. Working Track through 1200 UTC TAFB Satellite- Blue Square SAB Satellite- Black Square Microwave- Green (Circle) Air Force Aircraft- Red Triangle NOAA Aircraft – Blue Triangle Storm Analysis- Position Estimate

6. 29/1745 Determining Initial Location 29/1721 29/1318 SSMIS 29/1525 TRMM

7. Computing Initial Motion (Speed) About 102 n mi during past 12 h yields 8-9 kt

8. About 300 degrees Computing Initial Motion (Direction)

9. -NHC estimates cyclone “size” via wind radii in four quadrants -NHC estimates cyclone “size” via wind radii in four quadrants Tropical Cyclone Wind Radii How big is the storm? NE SE SW NW radii represent the largest distance from center in particular quadrant leads to an inherent over- estimate of radii, especially near land Wind radius = Largest distance from the center of the tropical cyclone of a particular sustained surface wind speed threshold (e.g., 34, 50, 64 kt) somewhere in a particular quadrant (NE, SE, SW, NW) surrounding the center and associated with the circulation at a given point in timeWind radius = Largest distance from the center of the tropical cyclone of a particular sustained surface wind speed threshold (e.g., 34, 50, 64 kt) somewhere in a particular quadrant (NE, SE, SW, NW) surrounding the center and associated with the circulation at a given point in time Wind radii in Hurrevac

10. Initialize models 6 Initialize computer models After determining the center, strength, motion, and size of the tropical cyclone, the hurricane specialist gives that information to a supercomputer to run the models

11. Receive model guidance and prepare forecast 6 Analyze and QC computer models 8 Prepare track, intensity, and wind radii forecasts

12. 12 Intensity Prediction Water temperatures Amount of moisture Wind shear

13. 13 Previous official forecast exerts a strong constraint on the current forecast Previous official forecast exerts a strong constraint on the current forecast – Can damage credibility by making big changes from one forecast to the next, and then having to go back to the original Windshield Wipering Tromboning Consequently, changes to the previous forecast normally made in small increments Consequently, changes to the previous forecast normally made in small increments We also strive for continuity within a given forecast We also strive for continuity within a given forecast – Gradual changes in direction or speed from 12 to 24 to 36 h, etc. Don’t Make Any Sudden Moves! (unless you really, really have to)

14. Dennis Guidance 6 July 1200 UTC Official forecast near model consensus in extreme western FL panhandle. 14

15. Dennis Guidance 6 July 1800 UTC Guidance shifts sharply westward toward New Orleans. Official forecast nudged westward into AL. 15

16. Dennis Guidance 7 July 0000 UTC Little overall change to guidance, but NGPI shifts slightly eastward. Little change in official forecast. 16

17. Dennis Guidance 7 July 0600 UTC Rest of the guidance shifts sharply eastward, leaving official forecast near the center of the guidance envelope (and very close to the actual track of Dennis. 17