Traders assign near-certainty to a 25°C minimum in Hong Kong on August 3, driven by the Hong Kong Observatory’s official daily observation confirming that exact low under typical subtropical summer conditions. Persistent high humidity, southeasterly flow from the South China Sea, and a stable thermal profile prevented overnight radiative cooling below this threshold, aligning with long-term August climatology where minimums rarely fall under 24–26°C without strong frontal passages or typhoon influence. The market-implied odds reflect verified station data rather than model projections, with negligible probability mass on other outcomes. Only a rare post-publication revision of the observatory record or a shift to an alternate measurement site could realistically alter the result.