Highest temperature in Hong Kong on August 18?

Platform comparison

Market context

On 18 August 2026, the Hong Kong Observatory will record the day's highest temperature in Celsius to one decimal place. Polymarket currently prices this contract at 0% YES across all temperature bands, reflecting either extreme illiquidity or a technical settlement state rather than genuine market conviction about the weather outcome. The market settles only after the Observatory publishes its "Daily Extract" data, which typically becomes available within days of the observation date but may face delays during typhoon season or system maintenance.

Hong Kong's August temperatures are remarkably consistent year-on-year, with historical daily maxima clustering between 31°C and 34°C. The Observatory's records show that temperatures exceeding 35°C occur in fewer than 5% of August days, whilst readings below 30°C are virtually absent during this month. August 2023 saw a peak of 34.5°C; August 2024 reached 34.8°C. These patterns suggest that the market's zero probability across all bands reflects settlement mechanics rather than meteorological impossibility—traders cannot yet position because the contract awaits finalised Observatory data.

The key catalyst is the Observatory's publication schedule. Traders should monitor the Hong Kong Observatory's website for the "Daily Extract" release for 18 August 2026, typically posted by late August or early September. Secondary factors include any announced system outages or data delays. The settlement window closes at 12:00 UTC on 18 August 2026, but actual resolution depends on Observatory data availability, which may extend resolution well beyond that timestamp.

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.

UK Frequently Asked Questions

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 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.

Is Polymarket legal in the UK?

Polymarket is accessible to UK traders but is not UKGC-licensed. It operates under US CFTC jurisdiction. UK residents face no domestic legal prohibition on using it, but UKGC consumer protections do not apply. For UKGC-regulated alternatives, Betfair Exchange and Smarkets offer similar prediction-style markets.

Do I pay tax on prediction market profits in the UK?

UKGC-licensed platform profits (Betfair, Smarkets) are typically tax-free gambling winnings for UK individuals. Polymarket profits involve USDC crypto transactions, which HMRC treats as Capital Gains Tax events. Keep full transaction records and report via Self Assessment if gains exceed £3,000 per tax year.

How do I deposit on Polymarket from the UK?

UK traders typically fund Polymarket via Coinbase UK, Kraken or Revolut — buying USDC with GBP and transferring to a Polygon-compatible wallet (MetaMask, Coinbase Wallet). Polymarket's onboarding walks you through the bridging process. Typical GBP-to-USDC conversion costs 0.5–1%.