1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. NASA Hurricane and Severe Storm Sentinel (HS3) Observations for Testing Environmental Control of Hurricane Formation and Intensification

The long-term goal is to utilize the NASA Global Hawk unmanned aircraft observations to advance understanding of Atlantic tropical cyclone formation and intensification. OBJECTIVES Advancement in the understanding and prediction of tropical cyclone formation and intensification requires observational studies of the combined effects of vertical wind shear, evaporational cooling in saturated convective-scale downdrafts, and the physical processes occurring along two air streams: (i) an equatorial source of warm, moist air with maximum winds in the lower troposphere; and (ii) a subtropical source of cool, dry air with maximum winds in the mid-troposphere. Although a mesoscale convective circulation is considered to be an essential element, it is hypothesized that the environmental properties in the two air streams control the timing and location of the formation of the tropical cyclone. Global Hawk observations are required along both air streams flowing into the region of the pre-tropical cyclone seedling. The objectives are to document the environmental conditions and the physical processes that lead to the spinup of the mesoscale vortex that becomes the inner core of the tropical cyclone to the southeast of the synoptic-scale circulation center, but inhibit formation to the northwest. The two long-duration, high altitude NASA Global Hawks devoted t