Strong El Niño conditions strengthening into fall 2026, with sea surface temperatures already exceeding 2°C above average and high odds of a very strong event, represent the dominant driver tilting trader consensus toward lower Seattle September totals near the historical 1.6-inch average. This pattern favors a southward-shifted storm track and enhanced ridging over the Pacific Northwest, suppressing onshore flow and atmospheric river activity that typically accounts for up to 57% of autumn precipitation in the region. Short-term National Weather Service guidance shows modest early-month rain but aligns with broader seasonal outlooks projecting below-normal accumulation along the coast. Differentiation among the tightly bunched bins hinges on the precise timing and intensity of any late-September frontal systems or marine pushes, which remain uncertain given model spread and the evolving ENSO state.