East of Iguassu Falls and the small piece of Argentina that sticks into the eclipse track, the Moon's shadow crosses an extensive area of rolling hills that grow gradually in height to form the 2000 meter high Serra do Mar that guards the Atlantic coast of Brazil. In November, the region is alternately affected by moist unstable air masses from the north and cooler southerlies from higher latitudes. Cold fronts that separate the two air masses can generate large areas of heavy cloud and bring poor eclipse prospects. Movement of fronts is impeded by the mountains and bad weather may linger in the area for several days, spawning a series of small rainy disturbances that keep the skies from clearing. Though they are not high mountains, the Serra also provide some blocking of moist airflows from the Atlantic, preventing them from moving into Argentina and Paraguay. Figure 9 shows this as a small decrease in sunny skies near Criciúma and along the Atlantic coast. In particular, the coast itself at 49 deg W is cloudiest of all. The statistics in Table 14 reflect this climatology as well. For instance, compare Posadas and Alegrete with Florianapolis and Porto Alegre.
It is a good rule to avoid mountains during an eclipse, particularly those in which a nearby ocean is available to supply moisture. Valleys have an unfortunate tendency to fill with cloud as second contact approaches and it is difficult to find a site with reliable downslope drying winds in the jumble of terrain. The eclipse track through Brazil is just such an area and the statistics bear out its poor ranking. It has one tempting asset - a four minute eclipse. It is advisable to use weather forecasts a day or two ahead of time to plan your location. However, a long trip may be necessary to find better weather, perhaps into Argentina or Paraguay.
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