Persistent southwest monsoon (Habagat) activity is the dominant driver, with PAGASA forecasting 50–100 mm of rainfall and widespread thunderstorms over Metro Manila through September 6. These conditions produce extensive cloud cover, elevated humidity near 85–95%, and reduced solar insolation, limiting daytime heating and capping maximum temperatures. Official model guidance and recent observations indicate highs of 28–29 °C, consistent with the market’s emphasis on 29–31 °C outcomes. Historical September climatology shows average maxima near 30–31 °C, but the current wet pattern has suppressed values below that baseline. Forecasters note typical model spread of 1–2 °C tied to exact timing and intensity of convective cells, keeping implied probabilities clustered around the observed range while acknowledging potential for brief clearing that could allow a 30–31 °C spike.