A case study of heavy rainfall associated with weak cyclogenesis in the northwest Gulf of Mexico

Aspects of the case include: 1) upward of 50 cm of rain along the extreme southern coast of Texas and 2) the brief occurrence of minimal strength tropical-storm conditions in a weak baroclinic marine environment. A crucial antecedent condition to rainstorm formation was the creation of a low-level baroclinic zone over the northwestern Gulf of Mexico due to the southward advance of drier and slightly cooler air behind a cold front. Four factors were responsible for rainfall concentration along the coast: 1) a northward-moving 700-mb trough and embedded vorticity maximum, 2) an eastward-propagating upper-tropospheric disturbance in the midlatitude westerlies over the southern US to the north of a subtropical ridge line over Texas and Louisiana, 3) the formation of a weak midtropospheric baroclinic zone over the extreme north-western Gulf of Mexico, 4) the existence and maintenance of a weak north-south-oriented baroclinic zone along the Mexican coast in the lower troposphere. -from Authors