Highlight: MJO strengthens, expands eastward in Pacific.
Fig. 1: NOAA/NHC 5-day forecast track for Hurricane Ian.
Discussion: Typical of a La Nina climate, the Madden Julian oscillation (MJO) has a tendency, to reside in the warmer than normal eastern Indian Ocean/West Pacific tropics with reluctance to shift eastward toward cooler equatorial waters. This scenario is observed during the northern hemisphere 2022 summer months. However, the MJO has recently developed an eastward reach to the tropical West Pacific and is forecast by ECMWF during the next 2 weeks to strengthen in phase_4/phase_5 (Fig. 1).
During an active MJO phase_4/phase_5 (Indonesia and vicinity), tropical/subtropical convection (heavy rain) is enhanced and leads to a wet monsoon signature for the maritime continent longitudes plus increasing risk of tropical cyclone activity in the West Pacific (Fig. 2). Conversely, MJO phase_4/phase_5 usually produces subsidence and a dry climate across South America and South Africa.
The most recent 15-day percent of normal rainfall forecast for the tropical/subtropical East Indian/West Pacific Ocean areas features widespread heavy rainfall including increased risk of additional tropical cyclones (Fig. 3). Included in the increased wet weather risk is Australia through the first third of October.
Fig. 2: Convection (blue)/subsidence (orange) climatology for MJO phase_4/Phase_5.
Fig. 3: GFS 15-day percent of normal rainfall forecast for the East Indian/West Pacific Ocean basins.