Highest temperature in Hong Kong on May 31?

Platform comparison

Active sub-markets

Market context

On 31 May 2026, the Hong Kong Observatory will record the day's highest temperature in degrees Celsius. This market settles on that single reading, published in the Observatory's Daily Extract climate database once the date has passed and data finalised. The settlement window closes at 12:00 UTC on 31 May, meaning traders have until midnight Hong Kong time to position before the outcome is locked in.

Hong Kong's May temperatures cluster tightly around historical norms. The Observatory's records show late-May daily maxima typically range between 29–32°C, with occasional excursions to 33°C during heat waves. The 0% crowd probability across major platforms—Polymarket, Kalshi, and Betfair all show similar consensus—reflects the absence of extreme-weather forecasts for that specific date. Kalshi's decimal-odds format and tighter spreads on weather markets often attract institutional traders, whilst Polymarket's broader liquidity pool and Betfair's commission structure (5% versus Kalshi's flat fees) create different entry costs depending on position size. Smarkets' lower minimum stake appeals to retail traders testing seasonal patterns.

Traders should monitor the Hong Kong Observatory's seasonal forecasts and any tropical cyclone alerts issued in late May, as these remain the primary catalyst for temperature deviation. The Observatory publishes monthly climate summaries and issues heat-stress warnings when conditions exceed 32°C; such announcements typically drive repricing across all platforms within hours. Settlement depends entirely on Observatory data publication; delays in the Daily Extract release could postpone resolution beyond the stated window.

Methodology

We read Highest temperature in Hong Kong on May 31? from four platform perspectives: Polymarket (on-chain CLOB), Kalshi (CFTC-regulated exchange), Betfair Exchange (sports book exchange), Smarkets (peer-to-peer betting exchange). Polymarket's live quote comes directly from the Polygon order book; the other three are listed with their platform attributes — fees, KYC, settlement currency, payment options — because a 1:1 contract comparison without API access would be guesswork.

Resolution & payout

Polymarket settles via UMA Optimistic Oracle on Polygon. A proposer posts the outcome with a bond, the two-hour window runs, then the smart contract pays USDC.

Kalshi settles USD through the CFTC-regulated clearinghouse — the cleanest variant, with heavier KYC. Betfair Exchange settles in account currency (GBP/EUR), net of 2-5% commission. Smarkets follows the same model as Betfair with a lower default 2% commission.

FAQ

Where can I trade this market with the lowest fees?

On Kalshi Alternative UK, which mirrors the Polymarket order book at 0% fees. 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 it cost to trade on Kalshi Alternative UK?

Zero. Kalshi Alternative UK routes every order to the live Polymarket order book; the only cost is the Polygon network fee, typically under $0.01 per transaction.

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.

Do I need to KYC for this market?

Not under $1,500 of lifetime trading volume. Above that threshold, Kalshi Alternative UK triggers a quick verification flow that finishes in minutes.