Persistent subtropical high pressure and elevated dew points near 75°F are anchoring Miami's overnight lows near seasonal norms of 79–81°F for August 17, producing the tight 39.5% and 37% market shares on 80–81°F and 78–79°F. High atmospheric moisture limits radiational cooling despite mostly clear skies, while light southeast winds and urban heat retention further compress the diurnal range. Minor model differences in boundary-layer mixing or brief cloud increases could tip the minimum across the 79°F threshold. No tropical systems or frontal passages are expected to alter the pattern before dawn on the 17th, keeping trader focus on short-term forecast refinements from the National Weather Service.