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280A. A. MACHADO ET ALLIwas tested through the Kolmogorov-Smirnov testand the homogeneity of the same ones through theLevene test (Zar 1999).Results and DiscussionIn the period between the years of 1979 and2008, 40 events of significant wave height (Hs)above 6 m occurred considering as reference theposition of (32°54’S, 50°48’W) at 100 m waterdepth. The yearly mean number of events was 1.33with a minimum of 0 events and a maximum of 4events in the year of 1999. The standard deviationwas 0.958/year.The ANOVA result of the 10 groups joinedat 3 years interval shows no significant difference inthe number of extreme wave height events along the30 years period (F(9, 20) = 1.4815, p = 0.22141(Fig. 2A). The correlation graphic between thenumbers of events and the thirty 30 years periodshowed a positive but weak correlation (r = 0.30636)(Fig. 2B).Anumber of eventsBnumber of events4,54,03,53,02,52,01,51,00,50,0-0,5-1,01979-1981 1985-1987 1991-1993 1997-1999 2003-20051982-1984 1988-1990 1994-1996 2000-2002 2006-20083 years4,54,03,53,02,52,01,51,00,50,0-0,51975 1980 1985 1990 1995 2000 2005 2010yearFigure 2. (A) Mean of the number of extreme events ofthe 10 groups, Vertical bars denote 0.95 confidenceintervals, (B) Correlation of the number of extreme eventsover the study period, the dashed line denote 0.95confidence intervals and the continuous line denote theregression line.Webster et al. (2005) found an increase inthe number of tropical cyclones and cyclone days aswell as tropical cyclone intensity over the past 35years, in an environment of increasing sea surfacetemperature. A large increase was seen in thenumber and proportion of hurricanes reachingcategories 4 and 5. The largest increase occurred inthe North Pacific, Indian, and Southwest PacificOceans, and the smallest occurred in the NorthAtlantic Ocean.From the analysis of the meteorologicalscenarios, four patterns of synoptic situationscapable of generating extreme events were identified(Fig. 3):• PATTERN I: Cyclogenesis in the southernArgentinean coast with a displacement to the eastand a trajectory between 47.5°S and 57.5°S;• PATTERN II: Cyclogenesis in the southernUruguayan coast with a displacement to the east anda trajectory between 28ºS and 43°S;• PATTERN III: Cyclogenesis in the southernUruguayan coast with a displacement to thesoutheast and a trajectory between 32°S and 57.5°S;• PATTERN IV: High-pressure center generatingan easterly wind.Was not observed at the study area asignificant difference in the frequency of thepatterns of cyclone trajectories along time. Thepattern with the greatest number of extreme eventswas Pattern II with 22 of the 40 +1 events. Eleven(11) events were associated with Pattern III and four(4) events were associated to both Pattern I and IV.The value of 41 related to the sum of all the patternsis due to an event that occurred on 07/21/1996, inwhich, two parallel extra-tropical cyclonesresembling Patterns I and II occurred simultaneously.Case StudiesIn this section, a selection of extreme seastate events was used to assess both, the specificmeteorological scenarios associated, and theresponse that was observed on the coast in terms ofbeach erosion.July 21 th , 1996An extreme wave height event occurred onJuly 21 th , 1996. The meteorological scenario showstwo extra-tropical cyclones parallel to each otherrepresenting Patterns I and II. Due to its eastern pathand the following of a high pressure system in therear, a long southwest wind fetch of more than 3000km was formed over the Atlantic off the SouthAmerican coast (Fig. 4).Pan-American Journal of Aquatic Sciences (2010), 5(2): 277-286