Much of our moisture originates from the tropics this time of year. The LHS chart shows tropical moisture (rising air at high altitude) over Australian longitudes (green shading). Similarly, RHS charts for the last 2 weeks, with low air pressure off eastern and northern Australia. Tracking this tropical moisture can help understand when rain-bearing systems are more likely.

The CPC (US) reports the Madden-Julian Oscillation (MJO) being “better organised” in Phase 5 this week (Australian region). The dynamical model spread for the next move of the MJO remains high, as ensemble means favour a decline of the intraseasonal signal over the Maritime Continent and western Pacific likely due to destructive interference with the ongoing La Niña. This limits forecast confidence on the predicted evolution and strength of the MJO into late December.

For a basic MJO explainer and why we need to watch the MJO, see the following animation here: https://www.youtube.com/watch?v=SwoB-2nSnJ0