Recent Met Office guidance for London on September 26 points to a daytime maximum of 21°C under partly cloudy skies with light westerly winds, underpinning the near-even trader consensus around 20–21°C. Model runs show limited diurnal warming from modest September insolation, with high pressure favoring stable conditions and minimal cloud break that could push readings slightly higher or keep them capped near 20°C depending on exact timing of any thicker cover. Historical September averages near 18–20°C provide context, while the tight spread reflects genuine forecast uncertainty in boundary-layer mixing and short-term steering patterns ahead of tomorrow’s official observations.