**Persistent southwest monsoon (Habagat) activity and associated cloud cover, scattered rains, and thunderstorms are the dominant factors keeping overnight lows in Manila near 23–24 °C on September 10.** Official PAGASA guidance for Metro Manila explicitly forecasts a 24–31 °C range under cloudy skies with scattered showers, consistent with recent station observations showing a 24.5 °C minimum early on the 10th. High humidity (often 85–95 %) and light winds limit radiational cooling, while daytime convection and rainfall further suppress the diurnal temperature range. Ensemble model guidance and local forecasts converge on nighttime minima of roughly 25–26 °C (77–79 °F), but recent trends of slightly cooler mornings amid ongoing monsoon flow support the market’s heavy weighting toward 23–24 °C. No major tropical cyclone or abrupt shift in steering patterns has emerged in the past 24–48 hours to alter this setup, and traders are pricing the outcome near official agency thresholds rather than historical September averages. Updated PAGASA briefings and the next model runs remain the key near-term catalysts.