National Weather Service and NOAA short-range forecasts highlight abundant Gulf of Mexico moisture and a persistent trough of low pressure as the main drivers of scattered thunderstorms and measurable rain on September 5, 2026, concentrated across the Southeast, Florida, and Gulf Coast states where afternoon PoP values reach 40-80%. Weak disturbances traveling along the trough, combined with high dew points and heat indices above 100°F, favor convective development during peak heating hours. In contrast, the Northeast sees a cooler air mass limiting activity, while the Southwest contends with separate monsoonal moisture. Traders monitoring market-implied odds should watch the next NWS model runs and local office updates, which refine precipitation timing and amounts critical to resolution thresholds.