The Influence of Vertical Wind Shear and the El Niņo-Southern Oscillation on Hurricanes in the Tropical Atlantic

Vertical wind shear is a significant factor in the formation and sustenance of hurricanes. With greater shear, it's more difficult for the core of a storm to stay organized. Because typical winds in the Atlantic follow a similar pattern to that of El Niņo's winds, the resulting shear is greater than average, while in La Niņa years the opposing patterns create less vertical shear. Uncoupled Weather Research and Forecasting (WRF) model runs at 27 km resolution were compared against observations from the National Centers for Environmental Prediction's (NCEP) reanalysis for the years 1981-2000. WRF model output consistently contained stronger wind shear than NCEP and tended to have more tropical cyclonic activity, contrary to known hurricane dynamics. However, both NCEP and WRF were sensitive to the influence of ENSO, showing deviations from the mean for El Niņo and La Niņa seasons in both hurricane activity and average vertical wind shear. Although WRF accounted for the influence of ENSO, the higher shear and simultaneous increased tropical cyclonic activity compared to observational data suggest possible biases in the model's dynamics. For long-term climate modeling, the WRF model's biases could lead to overestimations in predicting the tropical Atlantic's vertical wind shear and hurricane activity.