Synoptic-Scale Environments of Predecessor Rain Events Occurring East of the Rocky Mountains in Association with Atlantic Basin Tropical Cyclones*
Monthly Weather Review
The synoptic-scale environments of predecessor rain events (PREs) occurring to the east of the Rocky Mountains in association with Atlantic basin tropical cyclones (TCs) are examined. PREs that occurred during 1988-2010 are subjectively classified based upon the synoptic-scale upper-level flow configuration within which the PRE develops, with a focus on the following: 1) the position of the jet streak relative to the TC, 2) the position of the jet streak relative to trough and ridge axes, and
... d ridge axes, and 3) the positions of trough and ridge axes relative to the PRE and to the TC. Three categories were identified from this classification procedure: "jet in ridge," "southwesterly jet," and "downstream confluence." PRE-relative composite analysis for each category reveals that, consistent with previous studies, PREs typically occur near a low-level baroclinic zone, beneath the equatorward entrance region of an upper-level jet streak, and in the presence of a stream of water vapor from a TC. Despite these common characteristics, key differences exist among the three PRE categories related to the phasing of a TC with the synoptic-scale flow and to the interactions between a TC and its environment. Brief case studies of PREs associated with TC Rita (2005) , TC Wilma (2005), and TC Ernesto (2006) are presented as specific examples of the three PRE categories.