Meso-Vortices Observed by WSR-88D in the Inner Rainbands of Hurricanes Irene and Georges

Meso-vortices were observed by WSR-88D in the inner most rainbands of both Hurricanes Irene and George. The objective of this paper was to document the existence of the meso-vortices and assess the environment of them in hurricanes. Also, correlation of meso-vortex occurrence and intensity trend of the hurricanes was examined.

Review of WSR-88D reflectivity data showed echo patterns associated with rotation were present in the inner most rainbands. Comma echo patterns, hooks, and appendages were apparent in the reflectivity data. Areas of three dimensional shear and mesocyclones were occasionally collocated with the associated reflectivity patterns. Examination of the 1-minute averaged surface winds with streamline and isotach analysis from the Hurricane Research Division revealed that the meso-vortices developed in an environment of confluence and sharp isotach gradient near the radius of maximum winds (RMW). Initially, the meso-vortices developed in association with strong convection on the east and north sides of the hurricane circulation centers in the inner most rainbands. On the north edge of the hurricane circulation centers the meso-vortices were found to move west along the leading edge of strong convection wrapping around the centers from the east to the west side. Definition of the meso-vortex associated reflectivity echoes diminished with movement of the meso-vortices south along the west edge of the hurricane circulation centers.

Linkage of meso-vortex occurrence in the inner rainbands with hurricane strengthening was not conclusive. The meso-vortex detected in Hurricane Irene occurred when it was trying to strengthen. Minimum central pressure dropped 5 mb in the hurricane following occurrence of the meso-vortex. In Hurricane George, meso-vortex occurrence was followed by a pressure rise of 4 mb before pressure falls occurred later in the afternoon and evening. Computer modeling of meso-vortices in the inner most rainbands of hurricanes might provide more answers on the short and long-term affects on tropical storms and hurricanes.