The Hong Kong Observatory’s monthly forecast for normal to below-normal October rainfall, driven by a persistent anticyclone aloft and a weak northeast monsoon, forms the main catalyst behind the 83% market-implied probability on the 70-120 mm band. This aligns with the 1991-2020 climatological normal of 120.3 mm while accounting for reduced tropical cyclone activity, which historically supplies the heaviest monthly totals. Early October observations show moderate accumulation without extreme events, and short-term models indicate mostly light or suppressed precipitation through mid-month. Trader consensus thus treats the 70-120 mm range as the most probable outcome consistent with official guidance, while assigning low odds to drier or wetter extremes given the forecast’s uncertainty range and potential late-month shifts.