Soil moisture plays an important role in meteorological and hydrological processes. This variable plays an important role in surface and atmospheric feedback. Until recently, the cost of the instrumentation has made soil moisture observations impractical. The NOAA Hydrometeorology Testbed (HMT) has set up one of its soil moisture observation networks in the Babocomari River Basin, in Southern Arizona. On 23 July 2008, a diurnally driven convective event within the HMT network caused a flash flood on the lower Babocomari River. This research addresses the meteorological setting and the hydrological response of the Babocomari River Basin during this flood event. The role of pre-existing soil water content on the streamflow response is also considered. The soil moisture observations throughout the Babocomari River basin are compared with the soil moisture estimates from the Noah Land Surface Model (LSM) running within the operational North American Mesoscale Forecast System (NAM). Analysis of this data shows that the Noah LSM depicted the lower basin as being drier, while it depicted the upper basin as being wetter, compared to observation data. These soil moisture differences could have implications for the streamflow of the Babocomari River during a flood event.