You may use GPM 10-km resolution satellite data (12-h latency) and extract the data over Karnataka. Today or mostly tomorrow morning you fill find the data for yesterday.
Link is https://gpm1.gesdisc.eosdis.nasa.gov/data/GPM_L3/
There is no easy means to get the insitu rainfall data. There is a good network of TRG (Telemetry Rain Gauge) setup across Karnataka by KSNDMC (state disaster monitoring cell). You can only access the data through a research collaboration. I had used their data for my research. Another option is through requesting for the data from Department of Economics and Statistics (DES) Karnataka. Note here you can get only the historical data and the network is only sparse.