Highest temperature in Hong Kong on May 31?

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Market context

On 31 May 2026, the Hong Kong Observatory will record the day's maximum temperature in degrees Celsius to one decimal place. This single data point—published in the Observatory's Daily Extract once finalised—will determine which temperature band resolves YES. The settlement window closes at 12:00 UTC on that date, though the actual temperature reading may not be available immediately after; traders must account for publication lag before the market can formally resolve.

Hong Kong's late May climate sits at the threshold between spring and early summer. Historical data from the Observatory shows daily maxima in this period typically range between 28°C and 32°C, with occasional excursions toward 33°C during heat waves. The 0% crowd probability suggests either an extreme upper-band threshold or a technical artefact in how the market's range brackets were constructed. Comparing against May 2023 and 2024 Observatory records provides the most reliable baseline for calibrating expectations; neither year produced anomalous readings that would invalidate seasonal norms.

For programmatic monitoring, the Observatory publishes its Daily Extract on a fixed schedule accessible via their climate data portal. Traders building conditional orders or automated alerts should target the specific URL structure of the Daily Extract rather than relying on secondary weather APIs, which may introduce rounding or lag. Regional weather systems—particularly the onset of the southwest monsoon and any tropical cyclone activity—drive material variance in late-May temperatures. The Hong Kong Observatory's official forecast issued in early June will be the first formal guidance; tracking their 10-day outlook from late May onwards provides the earliest signal for whether anomalous conditions are developing.

Methodology

We track Highest temperature in Hong Kong on May 31? on the five venues with material liquidity for prediction markets. Live odds come from the Polymarket Polygon order book — the only source that ships real-time data under an open licence. For Kalshi, Betfair and Manifold we list platform attributes (fee, KYC, settlement, payment) instead of fabricated odds, because their APIs use non-comparable contract definitions.

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?

On Polymarket Review 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.

Is this market available outside the US?

Polymarket Review UK is available in most jurisdictions where Polymarket isn't directly accessible. Polymarket itself is geo-blocked in the US/UK/EU. Always check local regulations.

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, Polymarket Review UK triggers a quick verification flow that finishes in 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.