Jakarta, a megacity in Indonesia with 10.4 million inhabitants often experiences short-duration heavy rainfall causing devastating damage to infrastructure and loss of life. However, few studies have investigated the local factors influencing mesoscale rainfall extremes (REs) around Jakarta. This study aims to use C-band Doppler radar (CDR) to characterise sub-daily REs and understand the changes of mesoscale spatial characteristics of diurnal rainfall variation due to land-sea breeze and topography affect REs on seasonal timescales. We use a six-minute CDR during 2009-2012 and one-minute stations data at the mountain, inland, and coastal sites in 2010. We performed quality control of CDR and established the Z-R (reflectivity-rainfall) equation to retrieve one-hour rain-rate estimates (Z = 8.745R^2.149). Our results show that the local effects play a role in generating rainfall over the region. A distinct diurnal peak in the mean of hourly intensity (h_int) and rainfall frequency (R_hr ≥ 1 mm/ h_{freq_1}) is found over the mountainous region of west Java. In the dry season (Jun-Aug), there is a delay in the peak of h_int and h_{freq_1} occurring at 15-18 Local Time (LT), while in the wet season (Dec-Feb) the peak starts at 12-15 LT. In Dec-Feb, at the coast, the R_{freq_1} reaches a peak in the morning (0-6 LT). There is seasonal variation in the hourly rainfall statistical distribution over the radar domain. The Probability Distribution Function shows that at higher rain-rates (10<R ≤100 mm), the driest season has a higher contribution of heavy rain-rates than in the Sep-Nov. Spatial maps of h_int and daily intensity (d_int) show that the highest amount of rainfall occurs in the Dec-Feb especially in the western part of the radar domain and the mountainous sites where rainfall exceeds 0.84 mm/hr and 20 mm/day, with the highest d_int consistently appears at the mountainous regions at all seasons.