Abstract
A case study is made of the Texas coastal rainstorm of 17–21 September 1979 in which upward of 50 cm of rain inundated the area. The precipitation developed along a weak baroclinic zone left in place by a trough passage at higher latitudes. A cold upper tropospheric vortex over the southwestern United States enabled relatively cooler and drier air to flow southward over the warmer waters of the western Gulf of Mexico. Differential heating and moistening along a Texas coastal front slowly destabilized the atmosphere and set the stage for a convective scale response.
A mesoscale cyclonic circulation formed near the southwestern end of the coastal front and along the western edge of a convective cloud cluster. Embedded within this circulation was a short-lived mesocyclone which achieved tropical storm strength for 12 h. The case is a specific example of a mesoscale circulation in which origin and evolution is controlled by synoptic scale patterns. The mesocale disturbance, once formed, moves northeastward parallel to the coast. It gradually moves into an environment more favorable for quasi-geostrophic intensification as the circulation expands in area.
