What is Prof. Grays seasonal hurricane forecast for this year and what are the predictive factors?
Prof. Bill Gray at Colorado State University in Fort Collins, Colorado (USA) has issued seasonal hurricane forecasts for the Atlantic basin since 1984. Details of his forecasting technique can be found in Gray (1984a,b) and Gray et al. (1992, 1993, 1994). Landsea et al. (1994) also provides verifications of the first 10 years of forecasting. A quick summary of the components follows: • * El Nino/Southern Oscillation (ENSO) – During El Nino events (ENSO warm phase), tropospheric vertical shear is increased inhibiting tropical cyclone genesis and intensification. La Nina events (ENSO cold phase) enhances activity. • * African West Sahel rainfall – In years of West Sahel drought conditions, the Atlantic hurricane activity is much reduced – especially the major hurricane activity (Landsea and Gray 1992). Wet West Sahel years mean a higher chance of low-latitude “Cape Verde” type hurricanes. This is also due to higher tropospheric vertical shear in the drought years, though there may also b
