Madden Julian Oscillation Rainfall Influence On Southeast Asia, Australia and South America in February

Highlight: Emerging Madden Julian oscillation intensity in the East Indian Ocean and influence on precipitation.

Fig. 1: The 40-day forecast identifying where tropical convection is strongest (green) revealing presence of the Madden Julian oscillation.

Discussion: The convective phase of the Madden Julian oscillation (MJO) is forecast to strengthen in the same position over the next 2 weeks possibly lingering into March (Fig. 1). To compensate for this vast region of convection, the downstream effect is an area of subsidence extending across South America. The influence on climate is profound. The immediate important influences include an expansive very heavy rainfall pattern over Southeast Asia, the eastern Indian Ocean and Indonesia while the influence on South America is to make the climate drier. Additionally, the persistent convection in the far West Pacific/East Indian Ocean tropics will increase central equatorial Pacific Ocean trade winds which should cause a recently weakened La Nina to regain some strength.

The convection phase of the Madden Julian oscillation is evident now. A large mass of convection stretches across the southern tropical latitudes from the East Indian Ocean to Indonesia (Fig. 2). The heavy thunderstorm pattern is also evident in the northern hemisphere tropics in this region (Fig. 3).

The influence of the stagnant and strengthening MJO on rainfall for Southeast Asia, the East Indian Ocean and Indonesia is to produce excessive rainfall. The GFS ENS is most profound with their wet forecast across Southeast Asia (Fig. 4). Interestingly, the GFS ENS is dry across Australia (Fig. 5). The prevailing Australian climate through summertime 2021-22 is generally wetter than normal. Normally, MJO presence in the East Pacific/Indonesia sector is wet for Australia. A concern is the Australia climate may be wetter than most model forecasts for the next 15 days while the Southeast Asia very wet forecast may be overstated.

Often overlooked is the subsidence phase of the MJO which is clearly evident across South America over the next several weeks. The influence is dry and drier (model) forecasts are well-supported for South America through the middle third of February. The current GFS ENS 15-day percent of normal rainfall forecast for South America features a very dry regime across Argentina which is well-supported (Fig. 6). The very wet forecast for Brazil is likely too wet.

Fig. 2: Satellite view of the convection phase of the Madden Julian oscillation in the East Indian Ocean to Indonesia region in the southern hemisphere.

Fig. 3: Satellite view of the convection phase of the Madden Julian oscillation in the East Indian Ocean to Indonesia region in the northern hemisphere.

Fig. 4: GFS ENS 15-day percent of normal rainfall forecast across Southeast Asia and Indonesia.

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

Fig. 6: GFS ENS 15-day percent of normal rainfall forecast across South America.