The closely matched market odds between a 73°F-or-below low and warmer outcomes stem primarily from divergence among National Weather Service and global forecast models on whether a transient cooler air mass will reach South Florida by May 20 or whether persistent subtropical moisture and southerly flow maintain typical overnight warmth. Historical May climatology shows Miami’s average daily minimum near 77°F, with recent ensemble runs indicating modest variability tied to steering patterns and boundary-layer humidity rather than any strong synoptic signal. Updated model cycles and official National Hurricane Center or local National Weather Service briefings over the next 48–72 hours will likely narrow the range as the event approaches resolution.