Explaining The Unusually Wet India to China Pattern

Fig. 1: The anomalous precipitation rate across Asia since June 1, 2020.

Discussion: During the past 2 months an arc of persistent heavy rainfall has extended from the western half of the tropical Indian Ocean northeastward across parts of India and northeastward from there into China and more recently Japan (Fig. 1). Another large area of wet climate has emerged over Western Indonesia.

Surrounding areas have been very dry particularly Western and Eastern Russia. The leading catalyst of this entire climate regime is a stalled moderate-strength Madden Julian oscillation over the western half of the equatorial Indian Ocean stretching westward across tropical Africa since June 1 (Fig. 2-3). Enhancing the MJO convection and possibly allowing the MJO to persist in this region is the consistent warmer than normal ocean surface to a region where water temperatures already very buoyant (Fig. 4). The heavy rain pattern in Western Indonesia is also related to the tendency for increased convective rains over anomalous warm water.

The MJO forecast reveals that for the first time in 2 months some movement is expected. The ECMWF forecasts MJO to shift east toward Indonesia the next 2 weeks (Fig. 5) which will cause the wet weather across Western Indonesia to (also) shift eastward (Fig. 6). So far, Australia looks unaffected by the MJO shift. However, forecast models may trend wetter for Australia in August given the MJO shift.

Fig. 2-3: The stalled MJO pattern in the western Indian Ocean since June 1.

Fig. 4: The warm SSTA pattern in the Indian/West Pacific Ocean(s).

Fig. 5-6: The MJO forecast indicates an eastward shift which causes advancing rains across Indonesia.