Highest temperature in Hong Kong on May 31?

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Active sub-markets

Market context

On 31 May 2026, the Hong Kong Observatory will record the day's maximum temperature in Celsius to one decimal place. This single data point will determine which temperature band resolves as correct. The settlement window closes at noon UTC on that date, though the Observatory typically publishes daily climate extracts with a lag of several days, meaning resolution may be delayed until early June.

Hong Kong's May temperatures are shaped by pre-monsoon conditions and increasing humidity as summer approaches. Historical data from the Observatory shows May daily maxima typically range between 28–32°C, with occasional spikes above 33°C during heat waves. The 0% crowd probability across major platforms—Polymarket, Kalshi, Betfair, and Smarkets—suggests either extremely wide resolution bands that make any single outcome unlikely, or that traders have not yet engaged with this market. Kalshi's binary structure and Polymarket's decimal odds framework would handle this differently; Kalshi requires a yes/no threshold, whilst Polymarket's range-based format allows fractional stakes across multiple buckets. Betfair and Smarkets' lay mechanics mean traders can express scepticism about any given band without committing capital to a competing outcome.

Traders should monitor the Hong Kong Observatory's seasonal forecasts and any tropical cyclone warnings issued by the Joint Typhoon Warning Center, as these can suppress daytime highs. The El Niño/La Niña status in early 2026 will also influence regional temperature patterns. No scheduled weather events or policy changes affect Observatory methodology, so resolution hinges entirely on observed conditions and timely data publication.

Methodology

This page compares Highest temperature in Hong Kong on May 31? specifically across Polymarket, Kalshi, Betfair Exchange and Smarkets. Live odds come from the Polymarket order book; the other venues' contract details are maintained manually because their APIs aren't directly comparable. Every CTA routes to Polymarket Alternative, which mirrors the Polymarket order book at 0% fees.

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 Polymarket Alternative, 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'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.

Do I need to KYC for this market?

Not under $1,500 of lifetime trading volume. Above that threshold, Polymarket Alternative 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.