Akinsanola AA and Aroninuola BA
The study diagnostically evaluate the atmospheric conditions that led to the heavy rainfall event of September 29, 2012 in Nigeria using data from Tropical Rainfall Measurement Mission Multi-Platform Analysis (TMPA 3B43v7) and European Centre for Medium-range Weather Forecast (ECMWF), Era-Interim reanalysis. The spatial pattern of precipitation, horizontal divergence of moisture flux and vertical structure of the zonal wind speed were investigated over the study area. Results show that the heavy rainfall event was only limited to the south of latitude 9°N within the study domain. Furthermore, strong moisture convergence (divergence) was observed in the lower (middle) troposphere during the pre-event days of September 27 and 28, 2012, implying strong upward motion of convectively unstable moist air over majority of the study area. This observation may be responsible for the heavy rainfall delivery that led to the flooding. Furthermore, a well-organized African Easterly Jet (AEJ) at 700 hpa and Tropical Easterly Jet (TEJ) at 200 hpa were respectively observed South of 9°N. It is worthy to note that during the pre-event days, the intensity of the AEJ was greater in magnitude. Disappearing TEJ and a well-organized AEJ was observed North of 9°N. This observation may be the reason why the heavy rainfall was majorly over South of 9°N. The distinctive appearance of the two summer easterly Jets South of 9°N and the observed moisture convergence at the lower troposphere may have impacted to a very large extent the development of deep moist convection that led to the heavy precipitation experienced over the region. The aforementioned findings may be responsible for the extreme rainfall over the study area.