Recent Met Office observations and forecast models for London on September 13, 2026, confirm a daytime peak of 23°C under mild, mostly cloudy conditions with light southwesterly winds and scattered light rain. This aligns with surface measurements from stations like Heathrow, where afternoon temperatures stabilized near that level amid above-average but not extreme early-autumn warmth. The market's near-certain pricing on 23°C reflects this strong observational consensus and the narrow resolution criteria for the daily maximum. Minor shifts remain possible only if final official reports from primary stations revise the peak by 1°C due to microclimate differences or exact timing, though current data make such adjustments improbable.