1. Tropical Cyclone Forecasts Dr. Richard J. Murnane Risk Prediction Initiative Bermuda Biological Station for Research, Inc.

2. Hurricane Landfall in Miami and Dade County Cat 1&2Cat 3, 4, 5 19101930195019701990 Hurricane Landfall per Year 210210 Year Landsea, 1997

3. Tropical Cyclone Seasonal Forecasting Strategy l Identify predictable global and local features that drive climate l Statistically relate features to tropical cyclone occurrence

4. Outline l Background on tropical cyclones –Necessary conditions –Forecast parameters l Seasonal forecasts –Basin-wide –Landfall l Real-time hurricane intensity forecasts –Numerical prediction –Theoretical Maximum Potential Intensity

5. Necessary Conditions l l Coriolis Effect l l Unstable Atmosphere l l Sea Surface Temperature > 26º C l l Trigger l l Little Vertical Wind Shear l l High Relative Humidity

6. Major Climatic Features Affecting Atlantic Basin Hurricane Activity l El Ni l El Niño-Southern Oscillation (ENSO) l l Quasi-biennial Oscillation l l Sea Surface Temperature (SST) l l West Africa Rainfall l l Atmospheric Zonal Wind Anomalies l l Sea Level Atmospheric Pressure

7. El Niño-Southern Oscillation Images from IRI web site Normal El Niño

8. US Hurricane Landfalls   Cat. 3 0.0 0.2 0.4 0.6 0.8 24680 Probability Number Landfalls Per Year El Niño Neutral El Viejo J. O’Brien & COAPS

9. 0.0 0.2 0.4 0.6 0.8 1.0 Cat 1Cat 2Cat 3 El Niño Neutral El Viejo Baroclinically Influenced Atlantic Storms: Hurricane Landfalls/year # Landfalls/year

10. Tropical Only Atlantic Storms: Hurricane Landfalls/year # Landfalls/year 0.0 0.5 1.0 1.5 Cat 1Cat 2Cat 3 El Niño Neutral El Viejo

11. Quasi-Biennial Oscillation (QBO) Arrows show stratospheric wind direction West Phase Enhanced Atlantic Hurricane Formation East Phase Suppressed Atlantic Hurricane Formation

12. Sea Surface Temperature Climate Prediction Center

13. Sea Surface Temperature Anomalies Climate Prediction Center

14. Seasonal Atlantic Hurricane Activity (1886-1991) 0 100 200 May June July Aug Sept Oct Nov Dec Jan-Apr

15. West African Rainfall Western Sahel Region Gulf of Guinea Region

16. Sahel Rain (1899 – 1990) 19001920194019601980 Standard Deviation Landsea et al., 1992 Year 2 1 0 -2

17. 1949 – 1990 0.64 IHD 7 Driest Sahel Years7 Wettest Sahel Years 14.43 IHD Gray & Landsea, 1992 Intense Hurricanes vs. Sahel Rain

18. Long-term Trends Year Standard Deviation N. Atlantic SST Anomaly NE Atlantic SLP Anomaly (neg) Sahel Rain Intense Hurricane Days 19501960197019801990 2 1 0 -2 Gray, 1998

19. Basin-Wide Seasonal Forecasts

20. Gray et al.’s Basin-wide Forecasts l Issued in: December, April, June, August l Forecast includes a variety of parameters: –Named Storms –Hurricanes, Hurricane Days –Intense Hurricanes, Intense Hurricane Days –Hurricane Destruction Potential –Net Tropical Cyclone Activity l Predictive Parameters Vary With Forecast

21. Gray et al.’s ‘98 Atlantic Basin Forecasts

22. Landsea, 1997

24. Elsner’s Atlantic Basin Forecasts l Uses subset of Gray variables –Zonal winds –West African rainfall l Divides storms into tropical only and baroclinically influenced –assumes climatology for baroclinically influenced storms (per year) –assumes climatology for baroclinically influenced storms (  per year) –Predicts tropical only storms using OLS l Calculates intense hurricanes using Poisson regression

25. Elsner et al. Forecast 1998 Atlantic Intense Hurricanes Elsner et al., 1998 01234560123456

26. August ‘98 Forecasts

27. Seasonal Landfall and Location Forecasts

28. Gray Landfall Forecast l Divides coast into separate sections l Uses Atlantic Basin seasonal forecast of “Net Tropical Cyclone Activity” (NTC) and SST anomalies to calculate total landfall probability l Distributes total probability along coast based on landfall climatology

29. Cat 1&2 Hurricane Landfalls Gray, 1998

30. Intense Hurricane Landfalls Gray, 1998

31. 1998 Landfall % Probability Forecast 36 8 39 10.2 34 33  4  7  5  6  8 Gray, 1998

32. Elsner Landfall Probability Forecasts l Uses “Logistic Regression” for predictions l Predictors include: –Zonal wind anomalies –Sea level pressures –QBO –West African rainfall

33. 1998 Location Forecast Elsner et al., 1998

34. Hurricane Intensity Forecasts

35. NHC Intensity Forecasts (1990-97) 25 20 15 10 5 Error (knots) 199019911992 1993 1994 199519961997 72 hours 48 hours 24 hours Avila, 1998 Year

36. Ginis et al.’s Hurricane Forecasts l Based on Coupled Ocean-Atmosphere Model l Full Ocean Model Reproduces Air-Sea Interactions and Improves Intensity Forecasts

37. Hurricane Opal Ginis, 1998

38. Maximum Potential Intensity (MPI) l Developed by Emanuel and Bister l MPI Controlled by Environmental Factors, e.g.: –Sea Surface Temperature –Upper Atmosphere Temperature –Relative Humidity l Doesn’t account for forward motion

39. Contours of Maximum Wind Speed (m/s) Emanuel and Bister, 1998 Sea Surface Temperature (ºC) Upper Atmosphere Temperature (ºC) 15 20 25 30 35 40 45 -100 -75 -50 -25

40. Maximum Potential Winds (m/s) Emanuel and Bister, 1998

41. Maximum Potential Wind (knots) Emanuel and Bister, 1998

42. Conclusions l Many of the seasonal forecast parameters are related to the necessary conditions for tropical cyclone formation l Basin-wide seasonal forecasts are easier to make than landfall forecasts but they are of less relevance l Realistic representations of the ocean are needed to improve tropical cyclone intensity forecasts