Rare Events of Stratus Clouds on the Northeast Coast of Brazil

One event of three consecutive days and another of four consecutive days of Stratus clouds were registered at the Maceio airport on the northeast coast of Brazil. This is a very rare phenomenon for equatorial regions and it was analyzed using the high resolution (10km) ETA model, NCEP reanalysis, satellite data and conventional data supplied by the Hydrometeorological Directory DHM-SERHI/AL and by the Department of Flight Protection of the Zumbi dos Palmares airport. Wave disturbance in the trade winds and weak ascendant movements at low levels (1000 and 925hPa) were identified. At the same time, anticyclonic curvature at high levels formed descendant movements and subsidence inversion. These vertical movements combined with a stable layer between 850 and 700hPa created a very humid layer at the low levels. The precipitation forecasted by the ETA model with 24h antecedence presented a satisfactory result for an average quantity of precipitation. Nevertheless, the spatial distributions of forecasted and observed precipitation were different. Precipitation during all days was not forecasted for the coastal region, and for the west region the forecasted precipitation was more intense than the observed ones.