Franchito SH, Gan MA, Rao VB, Santo CME, Conforte JC and Pinto O
September 2015 was an atypical austral winter rainy month. Rainstorms were observed in Sao Paulo State, Brazil (53oW-44oW; 20oS-25oS) with catastrophic consequences. In this paper the atmospheric conditions responsible for the rainstorms that occurred on 8th September 2015 in Sao Paulo State and their social and economic consequences were analyzed. The results showed that the rainstorms affected practically the entire Sao Paulo State causing floods and threw down trees, interrupting of the traffic on the streets and affecting the system of electric energy. Rainstorms accompanied by high winds and strong divergence at 200 hPa and ascending motion were observed due to intense squall line moving over Sao Paulo State. Satellite and radar images showed strong convective activity and the heavier rainfall (around 90 mm) in the center-east sector at 20:45 UTC. Hourly data from meteorological stations showed that the wind gust and the precipitation were higher than 65 km h-1 and 10 mm, respectively in almost the entire State. In Sao Paulo city, the rainfall was the highest for September in the last 20 years. The amount of precipitation was 3% higher than the amount expected for the entire September. Since each region of inundation in Sao Paulo city causes a daily damage higher than US$ 263,000,00 a great economic harm must be expected. A co-operative project between National Institute for Space Research (INPE) institution and Energisa Power Company is in progress aimed to mitigate the effects of adverse weather conditions as in the case of the rainstorm that occurred in 8th September 2015.