Strong El Niño conditions, with Niño-3.4 sea surface temperature anomalies already exceeding +1.8°C and models projecting further strengthening through fall 2026, represent the dominant driver of trader sentiment favoring below-average September rainfall in Hong Kong. This pattern typically weakens the East Asian monsoon trough and reduces tropical cyclone activity or steering patterns that deliver heavy precipitation to southern China during the month, when historical normals range from roughly 222–299 mm. Early-September observations and short-range forecasts show scattered showers and thunderstorms but limited widespread heavy rain so far, consistent with suppressed convective activity under the current oceanic-atmospheric setup. Market-implied odds clustering near or below 275–300 mm reflect this consensus while acknowledging residual uncertainty from potential late-month typhoon tracks or localized convective bursts that could still push totals higher.