Wet Pattern in Brazil Continues; Shifts South

Fig. 1-2: The Nov. 19-25, 2024, rainfall amount observations across South America and the CMC ENS 15-day percent of normal rainfall forecast.

Discussion: The rainfall across parts of Brazil and Bolivia has been in the 4-8-inch range during the past week (Fig. 1). Aerial coverage of the wet weather pattern is immense and includes most of Brazil (except northern areas) and Argentina (except western areas). Interestingly, the rainfall occurs during the subsidence phase (across the America tropics) of the Madden Julian oscillation (MJO) which normally inspires a drier South America climate. The 15-day outlook is best represented by the Canadian Ensemble which identifies a persistent heavy rain zone shifting south to Northern Argentina, Southern Brazil, and Paraguay (Fig. 2). The forecast trend is wetter. Dynamics to inspire the continuing wet weather are available especially in the medium range as another upper trough moves across the East Coast of Argentina with attendant cold fronts extending to Southeast Brazil.

In Australia, an upper trough brings a wave of heavy rain to the north and east continent through the weekend (Fig. 3). The 6-10-day period turns hotter although areas of heavy rain appear across northwest continent and on the Southeast Coast (Fig. 4). In the 11-15-day period, more areas of heavy rain are forecast in the Northwest and near the New South Wales/Queensland coastal border (Fig. 5). The convection phase of the MJO north of Australia inspires periods of heavy rain.

Fig. 3-5: The GFS 15-day percent of normal rainfall forecast across Australia.