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Tropical Cyclone Forecasts

Explore the factors influencing tropical cyclone occurrence and forecast parameters for hurricane intensity and landfall probability. Learn about the necessary conditions and major climatic features affecting Atlantic Basin hurricanes. Discover the seasonal forecasting strategy for predicting hurricane activity.

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Tropical Cyclone Forecasts

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

  2. 2 1 0 Hurricane Landfall per Year 1910 1930 1950 1970 1990 Year Cat 1&2 Cat 3, 4, 5 Hurricane Landfall in Miami and Dade County Landsea, 1997

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

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

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

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

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

  8. 0.8 El Niño 0.6 Neutral El Viejo Probability 0.4 0.2 0.0 0 2 4 6 8 Number Landfalls Per Year US Hurricane Landfalls ³Cat. 3 J. O’Brien & COAPS

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

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

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

  12. Sea Surface Temperature Climate Prediction Center

  13. Sea Surface Temperature Anomalies Climate Prediction Center

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

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

  16. 1900 1920 1940 1960 1980 Sahel Rain (1899 – 1990) 2 1 0 -1 -2 Standard Deviation Year Landsea et al., 1992

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

  18. N. Atlantic SST Anomaly NE Atlantic SLP Anomaly (neg) Sahel Rain Intense Hurricane Days Long-term Trends 2 1 0 -1 -2 Standard Deviation 1950 1960 1970 1980 1990 Year Gray, 1998

  19. Basin-Wide Seasonal Forecasts

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

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

  22. Landsea, 1997

  23. Landsea, 1997

  24. Elsner’s Atlantic Basin Forecasts • Uses subset of Gray variables • Zonal winds • West African rainfall • Divides storms into tropical only and baroclinically influenced • assumes climatology for baroclinically influenced storms (» 3 per year) • Predicts tropical only storms using OLS • Calculates intense hurricanes using Poisson regression

  25. Elsner et al. Forecast 1998 Atlantic Intense Hurricanes 0 1 2 3 4 5 6£ Elsner et al., 1998

  26. August ‘98 Forecasts

  27. Seasonal Landfall and Location Forecasts

  28. Gray Landfall Forecast • Divides coast into separate sections • Uses Atlantic Basin seasonal forecast of “Net Tropical Cyclone Activity” (NTC) and SST anomalies to calculate total landfall probability • 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 » 4 » 5 » 7 33 » 6 » 8 39 36 8 10.2 34 Gray, 1998

  32. Elsner Landfall Probability Forecasts • Uses “Logistic Regression” for predictions • 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 72 hours 48 hours Error (knots) 24 hours 1994 1993 1990 1991 1992 1995 1996 1997 Year Avila, 1998

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

  37. Hurricane Opal Ginis, 1998

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

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

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

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

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

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