Highest temperature in Hong Kong on July 4?

Platform comparison

Market context

The real-world event at hand is the daily maximum temperature recorded by the Hong Kong Observatory on 4 July 2026, measured in degrees Celsius to one decimal place. This single data point will determine the outcome of a prediction market where the current crowd-implied probability for a 28°C peak sits at 0% YES, despite external models suggesting a 68.5% chance for that specific threshold[1]. The divergence between the zero-implied probability on the platform and the substantial odds offered by cross-platform analysts highlights a significant pricing inefficiency that traders must scrutinise before settlement.

Historical climate data frames this probability gap, as July remains Hong Kong’s hottest month with average highs reaching 89°F (approximately 32°C) and recent daily peaks hitting 92.1°F (33.4°C) on 2 July 2026[3][5]. While the 2018 July mean maximum was 31.8°C, the current market pricing ignores the consistent thermal intensity of early July, treating a 28°C outcome as virtually impossible despite it falling within the lower bounds of typical summer variability[4]. This suggests the market is overreacting to recent extreme heat rather than accounting for the statistical likelihood of a slightly cooler, yet still warm, day.

Traders should monitor the Hong Kong Observatory’s finalisation of the “Daily Extract” for 4 July, as the market cannot resolve until this official data is published in the climatological archive[2][8]. The primary catalyst is the release of the “Absolute Daily Max” figure, which will supersede all forecast models and settle the contract at 12:00 UTC on 4 July 2026[2]. No further announcements are required, but the dependency on this specific dataset means the price will remain volatile until the Observatory confirms the final temperature, a process that typically concludes within hours of the day’s end[4]. The settlement window closes strictly at 2026-07-04T12:00:00Z, leaving no room for late data adjustments[1].

Sources: 1 · 2 · 3 · 4 · 5

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 Kalshi vs Polymarket. 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.

Do I need to KYC for this market?

On Polymarket directly, no — it's wallet-based. Intermediary brokers like Kalshi vs Polymarket trigger KYC only above $1,500 of lifetime trading volume; under that you trade pseudonymously with a single wallet address.