Abstract: Based on the surface station observation and sounding data, and the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis datasets (ERA-5), the synoptic characteristics of warm-sector rainstorms in southern Henan are investigated by the mesoscale analysis and induction for the weather condition of warm-sector rainstorms from May to September during the 2011—2020 flood season. The thresholds of environmental condition parameters related to warm-sector rainstorms with different circulation patterns are extracted by the percentile method. The results show that: (1) The warm-sector rainstorm plays a major during the flood season in southern Henan. Thirty-six warm-sector rainstorm days are identified from May to September during 2011—2020, accounting for about 53% of the total heavy precipitation days. (2) Warm-sector heavy rainfalls in southern Henan can be categorized into four types of synoptic conceptual models, including warm shear line, shear-subtropical high, strong southwest jet and cold front types. The shear-subtropical high type occurs most frequently, while the cold front type is the least frequent. The frequency distribution of warm-sector rainstorms for four types is closely related to the locations of their major weather systems. (3) Conditions with abundant water vapor in the whole layer, relatively strong deep vertical wind shear, moderate instability energy of the atmosphere and low-level southerly jet are favorable for the generation of warm-sector rainstorms in southern Henan. The specific humidity at 850 hPa, the depression of the dew point at 500 hPa, K-index, and the maximum lower-level southerly wind speed can serve as predictive indicators for the forecast of warm-sector rainstorms over southern Henan.