Abstract
Synoptic situations associated with strong southeasterly winds over the Rio de la Plata (RP) estuary are locally known as s__udestadas.__ This phenomenon affects the coast of Buenos Aires city and its outskirts with floods, normally accompanied with persistent rainfall.
Storm surge levels (river level minus the astronomical tide levels) were used to identify cases associated with sudestadas. Although there is a local belief that most sudestadas are caused by cyclogenesis during winter, they actually occur during the whole year, being indeed less frequent in winter. In addition, they are not necessarily associated with cyclonic circulation. The maximum frequency of sudestadas is observed during summer and at the beginning of spring and autumn. This annual distribution was similar when two different waterโlevel thresholds were used to characterize the storm surge.
The three principal components (PCs) of the atmospheric circulation field at 1000 hPa accompanying the sudestadas explain 75% of the variance. These patterns show that sudestadas are associated with either a combination of a highโpressure system to the south of the RP and relatively low pressure to the north (first and second PC modes) or a very deep lowโpressure zone to the north of the river (third PC mode). These cases are associated with southeasterly winds, which produce tide waves on the RP.
Almost all the sudestadas associated with the third PC occur in winter and they reach on average greater peak levels than the others. These cases are associated with an intense lowโpressure system north of the RP, which is typically due to the frequent cyclogenesis in that region. Copyright ยฉ 2004 Royal Meteorological Society