**Warm southerly airflow and high pressure under the ongoing UK heatwave are keeping overnight minima elevated across southeast England.** Official Met Office guidance for London on 13 August points to a daytime peak near 35°C, with the overnight low expected around 19–21°C amid mostly clear or partly cloudy skies and light winds that limit radiative cooling. Recent model runs show only modest night-time drops because the warm air mass and elevated dew points suppress temperature falls, consistent with the amber heat warning and reports of minima holding at 16–18°C or higher region-wide, with a chance of tropical nights above 20°C in the southeast. The tight clustering of market-implied odds around 18–19°C (with 20°C a clear third) reflects residual uncertainty in short-range forecast details: small differences in predicted cloud cover, boundary-layer mixing, or the precise timing of any subtle wind shifts can shift the recorded daily minimum by 1–2°C. Historical August climatology for London shows typical minima near 14–16°C, but the current anomalous warmth—part of a summer already tracking well above average—has pushed expectations upward. Traders are therefore focused on the next Met Office and ECMWF model updates and any late adjustments to cloud or wind forecasts that could tip the balance between 18°C and 19°C resolution.