Now that tropical cyclone season is winding down we enter the next persistent issue for meteorological winter 2020-21 which is La Nina storms. La Nina storms produce three types of high impact weather certainly evident in the SUN/MON forecast.
A La Nina climate is normally wetter than normal across northern and eastern Australia. However, November has been dry in these sectors. Contributing to the dryness is the subsidence phase of the Madden Julian oscillation at the tropical longitudes of Australia.
Forecast models have over-forecast rainfall across the dry-to-drought portion of Brazil consistently the past 30 days for both short-range and medium-range timescales. Forecast models have a tendency to turn northwestern South America wet with a fetch of that moisture across Brazil (at times). Instead the northwest South America dry pattern (and drought) persists and central/south Brazil rains are failing.
Last week the Nino SSTA regions warmed significantly and La Nina lost intensity. In the eastern equatorial subsurface robust cool water supply diminished indicating fuel to sustain La Nina is less plentiful.