National Weather Service forecast models currently project a daily high in the mid-to-upper 80s for Houston on May 18, driven by southerly flow and moderate humidity typical of late-spring Gulf Coast patterns, which supports the near-even market split between the 88°F-or-higher and 86–87°F buckets. Ensemble guidance shows limited spread around this range, with the primary uncertainty tied to the exact timing and extent of afternoon cloud cover or a weak sea-breeze front that could cap temperatures near 84–85°F in some runs. Historical climatology places the May 18 normal at 88°F, providing context for why traders assign only minimal probability below 84°F. Updated model cycles and the next official NWS forecast discussion are the key near-term data releases likely to refine these market-implied odds.