Highest temperature in Hong Kong on August 21?

Platform comparison

Market context

On 21 August 2026, the Hong Kong Observatory will record the day's peak temperature in degrees Celsius. This market settles on that single daily maximum reading, published in the Observatory's Daily Extract climate database. The current 0% implied probability reflects the market's inability to price an event nine months forward with any meaningful historical anchor, rather than a genuine forecast that temperatures will fail to reach any threshold.

Hong Kong's August temperatures cluster tightly around 32–34°C, with absolute daily maxima rarely exceeding 36°C even during heat waves. The Observatory's 30-year normal for August sits near 32.3°C; extreme readings above 37°C occur roughly once per decade. Traders comparing this market across platforms will notice Polymarket's decimal odds format (where 0% probability shows as 1.00) differs sharply from Kalshi's implied probability display, though both charge similar maker–taker fees around 2%. Betfair and Smarkets, by contrast, offer tighter spreads on weather contracts but require UK or EU residency; Polymarket's global KYC reach makes it the primary venue for this specific Observatory-linked settlement.

The key dependency is the Hong Kong Observatory's publication schedule. Data typically appears in the Daily Extract within 48 hours of the date in question, though the settlement window extends to noon UTC on 21 August to accommodate any delays. Traders should monitor the Observatory's website for any methodological changes or station relocations that might affect recorded maxima. Seasonal typhoon activity in late August could produce outlier readings; the 2015 heat wave pushed daily maxima to 36.1°C, a useful reference point for calibrating tail-risk pricing.

Methodology

This page compares Highest temperature in Hong Kong on August 21? specifically across Polymarket, Kalshi, Betfair Exchange and Smarkets. The live probability is the Polymarket mid; the comparison columns summarise each venue's fee structure, KYC, settlement currency and payment rails. Every CTA routes to Robinhood Prediction Markets, which mirrors the Polymarket order book at 0% fees.

Resolution & payout

Settlement is the biggest difference between the four platforms: Polymarket on-chain in USDC (instant), Kalshi USD via CFTC (T+1), Betfair and Smarkets in local currency via bank withdrawal (T+1 to T+3). On-chain settlement clears in minutes — the fastest payout path of the four.

FAQ

Polymarket vs Kalshi — which is better?

Depends on your location. Kalshi is CFTC-regulated, US-only with full KYC. Polymarket is global, on-chain, no KYC up to $1,500. Polymarket has ~10x higher liquidity but higher regulatory risk.

Which platform has the deepest liquidity?

Polymarket — by a wide margin. Top markets reach $50-500M volume, Kalshi ~$200M cumulative, Betfair similar. Deeper liquidity means your trade moves the quote less.

Is Betfair a Polymarket alternative?

Only partially. Betfair Exchange is UK-focused with a sports-betting emphasis; they have politics markets but with thinner liquidity than Polymarket. Settlement in GBP/EUR, 2-5% commission on winnings.

What about Smarkets as an alternative?

Smarkets is a UK betting exchange with a lower default commission (2%) than Betfair. Liquidity on political markets is below Polymarket, comparable to Kalshi. Geo-blocked in many jurisdictions.

Are all these platforms regulated?

No. Kalshi is CFTC-regulated (US). Betfair and Smarkets are UK Gambling Commission licensed. Polymarket operates without explicit regulation — a different risk profile than a regulated sportsbook.