Highest temperature in Hong Kong on May 21?

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Market context

Polymarket is pricing this Hong Kong Observatory contract at 0% YES, so the on-chain USDC position still implies no meaningful chance that the highest temperature for 21 May settles in the market’s specified Celsius band. Because settlement uses the Observatory’s “Absolute Daily Max (deg. C)” from the Daily Extract, the key question is the day’s actual peak reading in Hong Kong, not a forecast average or citywide mean. On Polygon, the conditional token only resolves once the Observatory finalises the daily extract, so traders are effectively holding or buying exposure to the single highest observed temperature, with no payout until that source data is published.

For context, late-May Hong Kong is typically warm and humid rather than extreme by local standards. Historical climate data and seasonal averages put daytime highs around the mid-to-high 20s Celsius, with May often warming into the 29–30C range on the hottest afternoons. Recent years have also shown a tendency towards more heat: the Hong Kong Observatory said 2025 was one of the city’s warmest years on record, with 53 very hot days and 54 hot nights, and the mean maximum temperature in that period was 28.9C. That backdrop matters because a prediction market like this is less about whether Hong Kong is hot overall and more about whether the day reaches an upper-tail reading strong enough to land in the relevant temperature bucket.

The main catalysts are the Observatory’s same-day readings, any updates to the Daily Extract, and whether cloud, rain, or maritime breezes suppress the afternoon peak. Hong Kong’s weather can turn quickly in late spring, so the final number may be lower than the early-day forecast if showers develop or if the heat peaks away from the Observatory site. Traders should watch the Hong Kong Observatory’s published daily extract for 21 May and any short-range forecast updates during the day, since the market cannot resolve until the source data is finalised.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

This page is a comparison snapshot: one live quote (Polymarket), four reference venues with their key attributes, and a single execution path — every trade button routes to PolyGram, which mirrors the Polymarket order book directly.

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?

On PolyGram, 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?

PolyGram 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.

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 it cost to trade on PolyGram?

Zero. PolyGram 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.