Persistent marine-layer stratus and strong onshore flow driven by the cool California Current and coastal upwelling keep adjacent Pacific waters near 55–58 °F, limiting San Francisco’s August 31 maximum. Latest National Weather Service guidance and ensemble runs indicate mostly cloudy skies with southwest winds of 10–20 mph, producing forecast highs of 62–65 °F—well below the 69.6 °F climatological average. Minor model differences in the timing of any afternoon clearing or wind strength create the tight clustering around the 64–67 °F bins that traders currently favor, while stronger marine influence would favor the lower end of that range. No significant synoptic change is expected before the period ends.