Traders see the highest temperature in London on September 28 centering on 18–19°C because short-range forecast models from the Met Office and ECMWF currently show a mild autumn pattern with a weakening high-pressure ridge allowing moderate Atlantic airflow. Ensemble spreads remain narrow around seasonal norms for late September, with cloud cover, wind direction, and any late-day clearing as the main variables that could shift the daily maximum by one or two degrees. Recent model runs have shown little change, keeping the distribution tight between 17°C and 21°C while underscoring the inherent uncertainty in boundary-layer processes that determine exact peaks. New guidance expected within the next 24–48 hours will provide the next clear test of these probabilities.