**Traders have converged on a 40°C daily maximum in Jeddah on September 15 because official station observations and multiple forecast models show the temperature peaking at that exact threshold amid typical late-summer Red Sea coastal conditions.** Clear skies, light variable winds, and high humidity have supported strong daytime heating without significant cloud cover or precipitation to moderate it, consistent with September climatology where averages reach the mid-30s °C and occasional peaks exceed 40°C. Real-time data from sources like local meteorological stations confirm the high has been attained, producing the market-implied certainty. A realistic challenge would require post-analysis revisions to station records or discrepancies between measurement sites, though such adjustments are uncommon once the diurnal cycle has passed.