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 market betting on whether the city’s highest temperature will breach a specific Celsius threshold. The Hong Kong Observatory records daily maximums to one decimal place, and settlement hinges entirely on their finalized “Daily Extract” data. With the crowd-implied probability at 0% YES, the consensus treats a high-temperature outcome as virtually impossible, suggesting traders expect conditions to stay well below the target range.

Historically, late July in Hong Kong often sees temperatures between 31°C and 34°C, with extreme days occasionally reaching 35°C or higher during prolonged heatwaves. However, the 0% pricing implies the market believes 2026 will follow a cooler pattern, possibly due to anticipated cloud cover, rainfall, or the influence of a tropical system that typically suppresses peak heat. Comparable cases from the past decade show that while record highs are rare, they are not unprecedented; the current pricing may overlook this tail risk, creating a potential value spot for contrarian traders betting on an underdog heat spike.

Traders should monitor the Hong Kong Observatory’s daily weather bulletins and any tropical cyclone warnings issued by the Joint Typhoon Warning Center, as these can drastically alter temperature outcomes. A recent forecast from the Observatory’s mid-July update suggests a mix of sunshine and scattered showers, which could keep temperatures moderate [1]. If a sudden shift in wind patterns or a rapid clearing of clouds occurs, the market may need to recalibrate its 0% stance, especially if the “Absolute Daily Max” approaches the upper end of the historical range.

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

At resolution the UMA oracle takes over: a proposer posts the outcome with a bond, any token holder can dispute within two hours. Without dispute the result is accepted and the smart contract distributes USDC instantly.

On Kalshi (CFTC-regulated) resolution runs through their in-house clearing engine in USD. Betfair Exchange settles after match end in the account's local currency. Manifold pays no cash — only its in-platform "mana" currency.

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 Who Will Win. 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's the difference between YES and NO shares?

A YES share pays $1.00 if the event happens, $0 otherwise. A NO share pays $1.00 if the event doesn't happen. The market price between 0¢ and 100¢ is the implied probability.

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.