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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. Plain Language Summary: A record‐breaking heavy rainfall event, the highest in the 156‐year historical records, hit Indonesia's capital, Jakarta, in early January 2020. The flooding induced by extreme rainfall caused tremendous damage to infrastructure and had significant socioeconomic impacts. This study examines the atmospheric driving mechanisms underlying this extreme event. We found that heavy rains were triggered by an increase in humid air due to the blocking of the northerly surge over Northwest Java by the southerly winds. This condition created conditions for the development of deep convection and heavy rain over the region. In addition, the large‐scale moisture convergence induced by some types of equatorial waves and Madden‐Julian Oscillation during the event further enhanced local moisture and supported the development of convective cells and extreme rainfall. Deepening the understanding of the atmospheric mechanisms driving this event may provide valuable information for forecasting precipitation extremes over Jakarta in the future. Key Points: An exceptionally high daily rainfall accumulation of up to 377 mm caused severe flash floods in Jakarta in early January 2020The extreme rainfall was mainly caused by convergence of moisture‐rich air due to an unusual blocking of northerly surges by southerly windsThe occurrences of equatorial waves and Madden Julian oscillation partly contributed to the enhanced local moisture by increasing low‐level moisture convergence [ABSTRACT FROM AUTHOR]

Extreme rainfall accompanied by strong winds hit the province of Bengkulu in the western coastal area of Sumatera Island during September 19-20, 2017, causing floods and landslides in Seluma and Central Bengkulu district. This extreme rainfall was recorded by Bengkulu Meteorological Station about 257.0 mm day -1 using rain-gauge observation. The spatial distribution of extreme rainfall cannot be seen if only using a rain-gauge observation in this location. The spatial distribution of extreme rainfall is needed to identify the impact of rainfall on landslides in large areas. The study aims to (1) develop the reconstruction of the spatial distribution of extreme rainfall using weather radar and (2) investigate the trigger that caused extreme rainfall by analyzing the synoptic-scale tropical waves. Each weather radar datum is saved in a Constant Altitude Plan Position Indicator (CAPPI). To get rainfall information, the CAPPI must be derived from Quantitative Precipitation Estimation (QPE) values. In this paper, we derived CAPPI using a Marshall-Palmer reflectivity-rain rate relationship. The result shows that rainfall formed on September 20, 2017, 21.00 UTC with total daily rainfall ranged between 176 and 247 mm in both districts and the mean of total daily rainfall has exceeded the average of monthly rainfall. The analysis of tropical waves suggests that only Kelvin waves were active and served as a possible trigger factor while the Madden-Julian Oscillation (MJO) and Equatorial Rossby (ER) waves were inactive during this extreme rainfall., Competing Interests: The authors declare that they have no conflicts of interest., (Copyright © 2020 Jaka A. I. Paski et al.)