The influence of environmental vertical wind shear on hurricane eye formation

Studies of tropical storms recognize eye formation as an important indicator of intensification toward a mature cyclone. However, the reason why some tropical storms form eyes while others do not is not well understood. Our goal is to identify large-scale environmental conditions that favor or inhibit hurricane eye formation. Although a variety of factors were considered, we focused on environmental vertical wind shear (EVWS) because it is often considered the most disruptive to storms. We compared nine North Atlantic basin storms from 2000-2008 for a 48-hour period centered on the time of eye formation or the time of peak intensity (if no eye formed). To select cases for detailed study, infrared and microwave satellite imagery, aircraft data, and best track data were used. Three categories were considered: storms that 1) successfully formed an eye (2001 Michelle, 2002 Isidore, 2005 Rita) 2) did not form an eye at all (2002 Chris, 2002 Edouard, 2005 Gamma), and 3) had a transient eye formation (2002 Gustav, 2005 Ophelia, 2008 Fay). We used Statistical Hurricane Intensity Prediction Scheme developmental data and Global Positioning System dropsonde data to compare these nine storms in terms of EVWS speed and direction. Storms that formed an eye had lower EVWS values than storms that did not form an eye at all. These results suggest that EVWS has a detrimental effect on eye formation. Understanding the structural changes in tropical cyclones as they intensify is essential for improving hurricane forecasting skill.