Evolution of the upper tropospheric outflow in Hurricanes Iselle and Julio (2014) in the Navy Global Environmental Model (NAVGEM) analyses and in satellite and dropsonde observations

Abstract

AbstractUpper tropospheric outflow was examined during the life cycles of two hurricanes in the eastern and central Pacific Ocean. The outflow from Hurricanes Iselle and Julio was evaluated by using analyses from the Navy Global Environmental Model, which were very highly correlated with satellite atmospheric motion vector and NOAA G‐IV dropsonde observations. A synoptic overview provided the environmental context for the life cycles of both tropical cyclones (TCs). Then, the outflow magnitude and direction within 6 radial degrees of each TC center were analyzed in relation to TC intensity, the synoptic environment, and inertial stability, with the following results. In both Iselle and Julio, the azimuthally averaged outflow magnitude was maximized initially more than 4 radial degrees from the center, and that maximum moved steadily inward during a 4 day intensification period and reached a position radially inward of 2° within 6 h of the time of maximum surface winds. Furthermore, the direction of the outflow in both TCs was related to the evolution of the large‐scale upper tropospheric flow pattern, particularly the phasing of subtropical jet ridges and troughs moving eastward north of both TCs. Finally, outflow channels were consistently bounded by regions of lowest (highest) values of inertial stability counterclockwise (clockwise) from the maximum outflow azimuth, a pattern that persisted throughout the life cycles of both storms regardless of intensity, environmental flow, and the number and direction of outflow channels present.