Current Met Office guidance for London on August 20 projects a daytime maximum of 23°C under a mix of sunny intervals and possible scattered showers, with ensemble forecasts from ECMWF and GFS clustering tightly around 22–23°C. This reflects a transitional synoptic pattern featuring moderate westerly flow and Atlantic air masses that limit strong warm advection, while variable cloud cover and light winds moderate peak insolation and boundary-layer heating. Recent model runs show reduced spread as the event nears, consistent with typical late-summer variability rather than heatwave conditions seen earlier in August. Traders assign near-equal weight to the leading bins because small differences in frontal timing or convective development could shift the official reading by 1°C at monitored stations. Updated high-resolution guidance and satellite observations over the next 48 hours will further constrain outcomes.