The market question
Polymarket asked what the highest temperature in Hong Kong would be on 25 August 2026. Resolution followed the Hong Kong Observatory’s Absolute Daily Max (°C) at the headquarters station (Daily Extract), recorded to 0.1°C and then binned into the integer degree that contains it—so “31°C” means any reading from 31.0 through 31.9.
The contract set was therefore a set of mutually exclusive temperature bins rather than a single binary. The report under review was issued on the day of the event itself.
What the council concluded
Three models participated: Gemini, GPT, and Grok, with Grok acting as chairman. The council’s formal action was BUY_NO, carrying a stated probability of 55% and confidence of 65%. At the same time it identified a single most-likely bin:
Council recommends BUY_NO (NO). Probability: 55%, Confidence: 65%. Resolution is the Hong Kong Observatory’s Absolute Daily Max (°C) for 25 August 2026 at the Observatory headquarters station (Daily Extract, to 0.1°C precision), binned into the integer degree that contains it (31°C = 31.0–31.9).
The graded pick—the outcome treated as most likely—was the 31°C bin, assigned 54% probability. In short, the council did not treat any other single integer degree as more probable than 31°C, even while framing its overall stance as BUY_NO.
How the probabilities sat
No separate order-book snapshot is preserved in the graded record beyond the council’s own numbers. What we have is internal: 54% on the 31°C contract as the modal outcome, a 55% headline probability attached to the BUY_NO action, and 65% confidence in that framing. Because the grade basis was “most_likely,” performance is scored on whether the 31°C bin actually resolved true and on the 54% probability attached to it.
What actually happened
The winning outcome was exactly the bin the council had ranked first: the Observatory high fell inside 31.0–31.9°C. The council was therefore correct on the graded pick. With a forecast probability of 0.54 on the realized outcome, the Brier score is (0.54 − 1)² = 0.2116—consistent with a modestly confident, single-bin call that landed.
Takeaway
Weather markets resolved to a precise official series leave little room for narrative after the fact; either the reading lands in the named bin or it does not. Here the council’s modal forecast matched the Observatory print. The Brier score of 0.2116 reflects a probability that was directionally right but far from certain—an honest mid-range success rather than a high-confidence lock. The episode is a reminder that, on tightly specified meteorological contracts, simply identifying the correct integer degree as most likely is already a usable edge, provided the probability is not overstated.
AI-generated analysis for informational purposes only. Not financial advice.