Highest temperature in Hong Kong on May 21?

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Market context

Hong Kong’s top temperature reading for 21 May will be taken from the Hong Kong Observatory’s “Absolute Daily Max (deg. C)” once the daily extract is finalised. The crowd-implied 0% YES means the market is effectively pricing no confirmed path to a publishable reading inside the settlement window, so the key issue is not the weather itself but whether the Observatory issues a final value for the date and whether that value lands in the listed band.

For context, Hong Kong in May is typically warm and humid rather than extreme: recent climate summaries put average May highs around 29°C to 31°C, with the month often producing several days in the upper 20s or low 30s. The Observatory said May 2025 was relatively dry and hot, with a maximum of 33.0°C on 22 May and rainfall far below normal. More broadly, Hong Kong has continued to post unusually warm records in recent years, including a sixth-warmest year in 2025, which matters because even modest late-spring surges can push daily maxima towards the low-to-mid 30s rather than the high 20s.

The main catalysts are the Observatory’s daily extract timing, any late data correction, and the short runway before the 12:00 UTC settlement cut-off. Traders should watch the Hong Kong Observatory climatology page for the final daily extract, plus live forecasts from the local bureau and major weather services if a ridge, trough, or rain band is expected to move through. From a market-access angle, German GlüStV rules can restrict participation for some users, while the US CFTC’s reach remains a background issue for US persons even where the event itself is weather-based. “No-KYC up to $1,500” generally means smaller positions may be opened with lighter identity checks, which can make this market quicker to access, but it does not remove jurisdictional limits or settlement-source requirements.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

Methodologically we separate two layers: the live probability (Polymarket mid-price) and the platform attributes (fee, KYC, settlement currency, payment rails). The odds column is filled only where we have clean data — that avoids the made-up numbers that get a network demoted when search engines cross-check against the source venue.

Resolution & payout

Polymarket-based markets settle through the UMA Optimistic Oracle on Polygon. A proposer submits the outcome, a two-hour challenge window opens, and unchallenged proposals finalise the resolution. Payouts settle automatically in USDC the moment the result is final — no bookmaker, no delay.

Kalshi-based markets settle in USD via the CFTC-regulated clearinghouse. Betfair Exchange settles in GBP/EUR net of commission. Manifold is play-money and does not pay out real funds.

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.

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.

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.