Recent research has shown that predecessor rain events (PREs), regions of heavy rainfall that occur well in advance of recurving tropical cyclones (TCs), can enhance mid-latitude precipitation. Since numerical weather prediction serves as a key component in developing precipitation forecasts, it is important to assess its performance with these high-impact rain events. Understanding the meteorological factors responsible for the influence TC-PREs have on mid-latitude precipitation will help forecasters recognize model limitations. This study investigated 1) the difficulties of simulating mesoscale processes and 2) the synoptic-scale interactions that contributed to the heavy precipitation associated with one TC-PRE event over the Southern Plains region of the U.S. on 6-9 September 2010.

Model output of Tropical Storm Hermine was retrieved from version 3.3 of the Advanced Research Weather Research and Forecasting (WRF-ARW) numerical weather model and compared with surface precipitation observations. Discrepancies were observed in the simulation, such as the under-estimated magnitude, western bias, spread, and structure characteristics of the precipitation. Very high moisture content was indicated by the high precipitable water values that accompanied Hermine as it moved further inland. Southerly winds associated with Hermine's circulation helped advect this rich moisture northward into Oklahoma and Arkansas. An approaching frontal boundary from the northwest served as a lifting mechanism to precipitate the moisture, and led to the development of the PRE. These observations emphasize the role TC moisture plays in producing PRE events, and how being able to quantify that effect will improve practices for effective TC-PRE precipitation forecasts.