High Temporal Resolution Analyses with GOES-16 Atmospheric Motion Vectors of Mesovortex Rapid Intensification in Subtropical Cyclone Henri (2021)

Abstract

Abstract Four-dimensional COAMPS dynamic initialization (FCDI) analyses with high temporal and spatial resolution GOES-16 atmospheric motion vectors (AMVs) are utilized to analyze the development and rapid intensification of a mesovortex about 150 km to the south of the center of the subtropical cyclone, Cyclone Henri (2021). During the period of the unusual Henri westward track along 30°N, the FCDI z = 300-m wind vector analyses demonstrate highly asymmetric wind fields and a horseshoe-shaped isotach maximum that is about 75 km from the center, which are characteristics more consistent with the definition of a subtropical cyclone than of a tropical cyclone. Furthermore, the Henri westward track and the vertical wind shear have characteristics resembling a Rossby wave breaking conceptual model. The GOES-16 mesodomain AMVs allow the visualization of a series of outflow bursts in space and time in association with the southern mesovortex development and intensification. Then the FCDI analyses forced by those thousands of AMVs each 15 min depict the z = 13 910-m wind field responses and the subsequent z = 300-m wind field adjustments in the southern mesovortex. A second northern outflow burst displaced to the southeast of the main Henri vortex also led to a strong low-level mesovortex. It was when the two outflow bursts joined to create an eastward radial outflow all along the line between them that the southern mesovortex reached maximum intensity and maximum size. In contrast to the numerical model predictions of intensification, outflow from the mesovortex directed over the main Henri vortex led to a decrease in intensity.