**Persistent southerly flow from the Gulf of Mexico and high humidity are keeping overnight lows elevated in the upper 70s for Houston on September 21, 2026.** Official National Weather Service and model guidance show the daily minimum temperature occurring overnight into or during the early hours of the 21st, with forecasts centering on 79–81°F under mostly clear to partly cloudy skies, light southeast winds, and dew points in the low-to-mid 70s. This pattern reflects typical late-summer conditions with minimal radiational cooling due to high moisture content and the absence of any frontal passages or drier air masses. Trader consensus, reflected in the market-implied probabilities favoring 78–79°F (31%) and 76–77°F (23.5%), aligns closely with this consensus forecast range while assigning lower weight to cooler outcomes that would require stronger northerly flow or clearer, drier conditions not currently indicated. Key differentiating factors include the strength of Gulf moisture advection and the timing of any subtle wind shifts that could modestly enhance or limit overnight cooling. Updated model runs and NWS briefings over the next 48 hours will provide the primary near-term catalysts for any shifts in positioning ahead of resolution.