   Journal of Coastal Research SI 75 1182 - 1186 Coconut Creek, Florida 2016 ____________________ DOI: 10.2112/SI75-237.1 received15 October, 2015; accepted in revision 15 January, 2015. *Corresponding author: oceaam@gmail.com © Coastal Education and Research Foundation, Inc. 2016 Synoptic Systems Generators of Extreme Wind in Southern Brazil: Atmospheric Conditions and Consequences in the Coastal Zone Arthur A. Machado †* , and Lauro J. Calliari † ABSTRACT Machado, A.A. and Calliari, L.J., 2016. Synoptic systems generators of extreme wind in southern Brazil: atmospheric conditions and consequences in the coastal zone. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1182 - 1186.Coconut Creek (Florida), ISSN 0749-0208. The coast of Rio Grande do Sul (RS), southern Brazil, suffers a seasonal variation due to the dynamics associated with the frequency and intensity of storms. These storms are mostly associated with high intensity extratropical cyclones that generate wind waves which can change a beach profile from its maximum accretion state to complete erosion during a period that can vary from few hours to a few days. Using the Generalized Pareto Distribution, we observe that the 0.01 probability density value of all the wind speed values studied was 17 ms -1 . Analyzing the storms that generate extreme winds (ie  17 m s -1 ), an increase in the number of extreme events to the coast of RS was observed over the past 66 years (1948-2013). The increase in the frequency of extreme events of wind, will modify and increase flooding, storm surge, and erosion along the coast. It was observed that the main weather systems generating strong winds to the shore of the RS are extratropical cyclones, which are mainly formed between parallels 30°S to 40°S, with two preferred trajectories, east and southeast, generating both erosion and storm surges. The majority of extratropical cyclones presentend propagation velocities between 20-40 km h -1 (61.97%). The months with the highest number of extreme events were June (22), followed by October (16). The consequences of storms in RS coast were: erosion of 45 m³m -1 , storm surge of 1.88 m, wind speed of 26.21 m s -1 and significant wave height of 8.79 m. ADDITIONAL INDEX WORDS:Extratropical cyclones, extreme events, storm surge. INTRODUCTION Atmospheric fronts and frontal systems are central components of weather (and hence, climate) over much of the world. These frequent phenomena (every few days over many extratropical regions) are associated with precipitation, dramatic changes in temperature and changes in wind (direction and speed), among other factors (Simmonds et al., 2012). Extratropical synoptic systems compose the daily weather patterns in the mid and high latitudes (Lim and Simmonds 2007). The extratropical cyclones can cause severe coastal damage, such as beach erosion and storm surge (Machado et al., 2010). Furthermore, intense cyclones and associated episodes of strong winds, high waves, and heavy precipitation are important in transmitting the effects of low-frequency climate variability to the environment and society (Graham and Diaz 2001). In Rio Grande do Sul (RS), southern Brazil, storms are frequently associated with high intensity extratropical cyclones, which generate wind waves that can alter a beach profile from its maximum accretion state to a completely eroded state over a few hours to a few days (Calliari et al., 1998, Machado et al., 2010). Machado et al. (2010) studied extreme wave events at RS shore and showed that both extratropical cyclones and anticyclones generate extreme waves in the South Atlantic. The southeast coast of South America is affected by atmospheric systems at synoptic and sub-synoptic scales, which are influenced by factors associated with circulations at large or local scales. Among the phenomena at the synoptic scale are frontal systems (Saraiva et al., 2003). Gan and Rao (1991) studied the surface cyclogenesis frequency over South America during a 10 year period and observed a larger number of extratropical cyclones in the winter (30.5 per year), followed by autumn (30.2 per year), spring (26.8 per year) and summer (20.7 per year). In addition to seasonal variations, Gan and Rao (1991) observed an interannual variation in the frequency of cyclogenesis over South America, with the incidence of higher cyclogenesis during El Niño years. Therefore, the present work aims to describe the distribution of wind speeds over 66 years (1948-2013) and the probability of occurrence of extreme wind speeds along the RS coast (southern Brazil). Furthermore, the synoptic propagating systems that generate these strong winds and their consequences in the coastal zone are explored. Background The Holocene barrier system of RS occupies the entire 620 km length of coast. Discontinuities in the barrier occur only at two sites: in the south, at Cassino (Figure 1), where the inlet of the Patos Lagoon is located, and in the north, at the inlet of Tramandaí Lagoon. Both inlets are permanently open because of a continuous and large discharge of fresh water through their entrances. The entire RS coastline is gently undulating and † Geological Oceanography Laboratory, Institute of Oceanography Federal Universityof Rio Grande - FURG Rio Grande, Brazil www.cerf-jcr.org www.JCRonline.org