Scott Braun

The Hurricane and Severe Storm Sentinel (HS3) EV-1 investigation conducted its first of three campaigns during September 2012. Based at NASA’s Wallops Flight Facility, HS3 used one of NASA’s Global Hawk Unmanned Airborne Systems to study the development and evolution of Atlantic tropical cyclones. The Global Hawk was equipped with three sensors: the NOAA/NCAR dropsonde system, the GSFC Cloud Physics Lidar, and the University of Wisconsin scanning high-resolution interferometer sounder (S-HIS). HS3 conducted a study of the outflow layer of Hurricane Leslie during transit of the Global Hawk from Dryden to Wallops. The remainder of the flights (five in all) focused on the evolution of Hurricane Nadine, the 5th longest-lived hurricane on record in the Atlantic. Nadine formed in association with a strong African Easterly Wave and had a very prominent layer of dusty Saharan air in its near environment. During the period when Nadine intensified to hurricane strength, the aircraft data suggest that the Saharan air, with the aid of strong vertical wind shear, was able to penetrate to near the interior circulation of Nadine and therefore likely contributed somewhat to Nadine’s slow intensification. After becoming a hurricane, Nadine quickly moved eastward to the region of the Azores. Despite high vertical wind shear, low sea-surface temperatures, and very dry environmental conditions, Nadine persisted for about 2 weeks as a tropical storm or post-tropical low, eventually re-intensifying into a Hurricane and reaching the highest intensity of its entire lifetime. In this talk, we will explore some of the possible reasons for Nadine’s maintenance and re-intensification.