Forecast models from Chinese meteorological sources and international ensembles indicate a multi-cloudy day on September 19 with a projected overnight low near 16–19 °C, driven by a shift from southerly to northerly flow that advects slightly cooler continental air while limiting clear-sky radiative cooling. Recent days have featured above-average warmth and high humidity that delayed the seasonal decline, yet the approach of a weak frontal boundary increases the chance of modest cooling; historical climatology places the long-term average low at roughly 15 °C. Model spread remains the dominant uncertainty, with some runs showing greater cloud cover or stronger northerly winds that could push the minimum a degree or two lower, while others keep readings closer to 20 °C. The near-even market split between sub-14 °C and 23 °C-plus outcomes therefore reflects traders weighting this narrow forecast envelope and the limited time remaining for new observational data or model updates to resolve the range.