Highest temperature in Hong Kong on July 21?

Platform comparison

Market context

Hong Kong faces its peak summer heat on 21 July 2026, with the Hong Kong Observatory set to record the day’s absolute maximum temperature in degrees Celsius. The prediction market in question tracks which temperature range will contain this peak, yet the crowd currently assigns a 0% probability to the YES outcome, implying near-certainty that the event will not occur within the specified bracket. This stark pricing suggests traders believe the forecasted high will fall outside the defined range, likely due to expectations of either significantly cooler conditions or a record-breaking spike beyond the upper limit.

Historically, Hong Kong’s July highs typically range between 31°C and 34°C, with extreme days occasionally reaching 35°C or higher under strong subtropical ridges. The 0% implied probability aligns with recent patterns where temperatures have remained stable within the 32–33°C band, making outliers less probable unless a sudden monsoon disruption or heatwave intensifies. Comparable cases from 2023 and 2024 show consistent clustering around 32.5°C, reinforcing the market’s conservative stance against unusual deviations.

Traders should monitor the Hong Kong Observatory’s daily weather bulletins and the latest tropical cyclone warnings, as these directly influence temperature outcomes. A recent update from the Observatory notes heightened uncertainty in mid-July forecasts due to shifting Pacific pressure systems, which could alter thermal conditions unexpectedly [1]. Key catalysts include the release of the “Daily Extract” containing the finalized “Absolute Daily Max” data, which will determine settlement once published after the 2026-07-21T12:00:00Z deadline.

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). That keeps the comparison honest — a single canonical probability across the row, with the venue-by-venue trade-offs spelt out in the columns next to it.

Resolution & payout

Settlement runs on-chain. Polymarket's contract logic separates YES and NO shares as conditional tokens; at resolution the winning share lifts to $1.00 and the losing one to $0. The outcome input comes from the UMA Optimistic Oracle, which secures against bad resolution with a bond + dispute window.

Once finalised, the smart contract pays USDC to the holders' wallets within minutes — no withdrawal fees beyond Polygon network gas. Kalshi settles in USD via CFTC clearance, Betfair in account currency net of commission, Manifold in play-money mana with no cash-out.

FAQ

Where can I trade this market with the lowest fees?

Polymarket is geo-blocked in the US/UK/EU. The easiest 0%-fee broker into the same order book is Best Prediction Markets UK. Kalshi charges up to 7% per trade; Betfair Exchange takes 2-5% commission on net winnings.

How does resolution work?

Through the UMA Optimistic Oracle on Polygon: a proposer submits the outcome, a two-hour challenge window opens, and USDC payouts settle automatically once the result is final.

What does Polymarket cost to trade?

Polymarket itself charges 0% — the only cost is the Polygon network fee, typically under $0.01 per transaction. Off-chain venues like Kalshi or Betfair charge 2-7% commission.

How fast are USDC deposits?

Polygon credits deposits after 12 confirmations — usually under 30 seconds. Withdrawals follow the same path and land back in your wallet within minutes.

How reliable are the quoted odds?

The YES/NO percentages are the live mid-prices of the Polymarket order book. On deep markets they move every few seconds; on thinner ones you'll see short plateaus.