Record-Breaking Precipitation in Indonesia's Capital of Jakarta in Early January 2020 Linked to the Northerly Surge, Equatorial Waves, and MJO

A record-breaking extreme rainfall event, the highest amount recorded since 1866, hit Indonesia's capital, Jakarta, in early January 2020. This torrential rainfall was mainly caused by the convergence of moisture-rich air due to an unusual blocking of cross-equatorial northerly surge over Northwest Java by the southerly winds induced by a cyclonic flow over the Indian Ocean. This condition caused a local increase in the amount of water vapor over Jakarta that eventually led to the formation of clouds and heavy precipitation. In addition, the concurrent occurrences of convectively active phases of equatorial waves (Kelvin, TD-type, and eastward propagating inertia-gravity waves) and Madden-Julian Oscillation during the event also partly contributed to the enhanced local moisture over the region by increasing low-level moisture flux convergence. Together, these large-scale dynamical drivers provided a convective environment that fostered the development of a massive rain-producing mesoscale convective system and, consequently, extreme rainfall over the region.

Automated summary

In early January 2020, Indonesia's capital Jakarta experienced a record-breaking extreme rainfall event. This rainfall was mainly caused by the convergence of moisture-rich air due to a blocking of cross-equatorial northerly surge and the presence of convectively active phases of equatorial waves and Madden-Julian Oscillation.