Highest temperature in Hong Kong on May 21?

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Market context

Hong Kong’s highest temperature on 21 May will be set by the Hong Kong Observatory’s final “Absolute Daily Max” reading for the day, with the market settling on the recorded Celsius range. May is typically a warm, humid shoulder month in the city: normal highs sit around 29°C to 30°C, while recent forecasts and climate summaries point to daytime peaks in the high 20s and low 30s rather than anything extreme. AccuWeather’s May outlook for Hong Kong shows highs of roughly 83°F to 94°F, and the Observatory said May 2025 was warmer than usual, with a monthly mean maximum of 30.0°C and the month’s top reading reaching 33.0°C.

The 0% implied YES price suggests the market is currently discounting any outcome that would settle into the relevant temperature band, so the main reference is whether 21 May turns into a broadly typical hot day or a brief spike above the seasonal range. WeatherSpark’s May climate data puts the warmest stretch in the final third of the month, with daily highs commonly around 86°F, which is consistent with an expected upper-20s to low-30s Celsius print. In practice, the final figure will be driven by whether cloud, rain and onshore flow keep the Observatory’s maximum suppressed, or whether a clearing, dry afternoon allows a short-lived peak.

The key catalysts are the Hong Kong Observatory’s day-of observations and any late forecast shifts tied to rain bands, a trough, or stronger subtropical ridge influence over southern China. Holiday Weather notes May rainfall in Hong Kong rises quickly through the month, with cloud cover and humidity often limiting sunshine, while the Observatory’s May 2025 review highlighted a drier-than-normal month under a stronger subtropical ridge. If a similar ridge builds again, the day could run close to or above 30°C; if showers and cloud dominate, the high may stay several degrees lower.

Sources: 1 · 2 · 3 · 4 · 5

Methodology

We track Highest temperature in Hong Kong on May 21? 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 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.

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.

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, PolyGram triggers a quick verification flow that finishes in minutes.