Trader consensus on the Polymarket distribution, with the highest implied probability on below-normal totals under 275 mm, reflects the Hong Kong Observatory’s September 2026 outlook for normal-to-below-normal rainfall amid a rapidly strengthening, potentially record El Niño. Equatorial Pacific sea-surface temperatures have risen sharply, with models projecting a very strong event peaking in November–December that typically suppresses South China Sea convection and favors high-pressure ridging over the region during the second half of the month. Early-September tropical cyclone activity, including systems crossing the northern South China Sea, introduces short-term rainfall potential, yet climatological analogs and dynamical guidance indicate reduced overall moisture transport. Key variables include the precise timing and intensity of El Niño teleconnections, the frequency and tracks of late-season tropical cyclones, and any deviations in the strengthening subtropical anticyclone. Forecast updates from the Observatory and major centers will refine these probabilities as the month progresses.