Recent dry conditions following the UK's record-hot summer of 2026, marked by prolonged high pressure and below-average rainfall, have tilted trader sentiment toward drier outcomes for London precipitation, with the 30-40 mm and sub-30 mm bins leading at 27.0% and 26.5% implied probability. The long-term September average near 50 mm reflects typical Atlantic frontal influences, yet lingering anticyclonic patterns and soil moisture deficits can suppress convective rainfall early in the month. Model divergence on the timing of seasonal transition to westerly flows keeps probabilities spread across 30-60 mm bins, with potential for late-month increases if low-pressure systems strengthen.