Variability and Predictability of Indian Rainfall During the Monsoon Onset Month of June

Summer‐mean Indian rainfall (June to September) decreases during a developing El Niño. Here we investigate the variability and predictability of Indian rainfall in each summer month with a focus on June, the onset month of the Indian summer monsoon (ISM). We find that Indian rainfall in June is affected by both concurrent and antecedent El Niño conditions, with a larger contribution from the latter. During the post‐El Niño June, rainfall decreases over central and northeastern India with anomalously extended premonsoon heatwaves as the positive sea surface temperature (SST) anomalies over the north Indian Ocean delay the onset of the ISM. Our results suggest that the prediction of Indian rainfall in June needs to consider concurrent SST anomalies over both the equatorial Pacific and north Indian Oceans. A better prediction of El Niño–Southern Oscillation and north Indian Ocean SSTs can improve the prediction of the ISM onset, the termination of premonsoon heatwaves, and Indian rainfall in June. Plain Language Summary The summer monsoon (June to September) brings over 70% of the annual rainfall to India. Even small deviations from the climatology can cause floods and droughts in this agricultural country, so the prediction of Indian summer rainfall is important. Indices representing concurrent El Niño–Southern Oscillation conditions in the Pacific have been widely used in predicting of summer‐mean rainfall over India. Here we show that including the concurrent Indian Ocean surface temperatures improves the prediction of the Indian monsoon onset, the termination of premonsoon heatwaves, and Indian rainfall in June. Key Points There are large regional differences from month to month in both the interannual variability and predictability of Indian summer rainfall Indian rainfall in June is affected by both concurrent and preceding winter El Niño conditions During the post‐El Niño July and August, positive Indian SAT anomalies are due to the north Indian Ocean warming.