Warm-Sector Heavy Rainfall over the Eastern China Plains: Identification, Characteristics, and Precursor Dynamic Signals

Abstract. Warm-sector heavy rainfall (WSHR) features small spatial scales, posing critical forecast challenges, while its fractional contribution to regional heavy rainfall and its short-term precursors remain poorly quantified. Drawing on 2021–2025 warm-season (June–September) observations from 493 surface rain gauges, ERA5 reanalysis, and a radar wind profiler (RWP) mesonet across the eastern China plains, we build an objective identification framework integrating automated front detection, warm-sector mask, and station-specific 99^th-percentile hourly rainfall thresholds to separate WSHR from other heavy rain events. We detect 477 station-based WSHR events alongside 6002 non-warm-sector heavy rainfall events. WSHR exhibits scattered spatial distribution, peaks in July–August, and preferentially occurs overnight, with rainfall onset concentrated 2000–0300 Beijing Time. Accounting for merely 5–10 % of annual heavy rainfall occurrences, WSHR has shorter durations yet comparable median rainfall accumulations and heavier extreme rainfall tails. On average, they contributed 13.8 % of the total heavy-rainfall accumulation, and locally 40–50 %. Composite ERA5 fields show that WSHR initiates within an 850-hPa moist tongue of high pseudo-equivalent potential temperature south of the front, superimposed on strengthening low-level moisture flux convergence. RWP composites based on 62 WSHR events reveal a characteristically low and strong low-level jet that becomes increasingly frequent before the onset of rainfall, accompanied by enhanced kinetic energy and shallow vertical shear below 3 km and an abrupt ascent increase centered at 1–2 km within the final hour. These kinematic signals from wind profilers offer valuable observational precursors for predicting localized WSHR across the eastern China plains.