Latest numerical weather prediction models from the National Weather Service and private ensembles indicate San Francisco's overnight low on September 5 will likely settle in the mid- to upper 50s°F, driven by moderate onshore westerly flow and a shallow marine layer capping radiative cooling under partly clear skies. Typical early-September conditions feature ocean surface temperatures near 52–56°F that chill incoming air, while a weakening North Pacific High reduces the inversion strength compared with peak summer, allowing modest nighttime drops without strong offshore winds or dense fog. Small forecast spreads arise from uncertainties in marine layer depth and exact wind timing, which can shift minimums by a degree or two across microclimates. Updated model runs and observations through tonight will refine these probabilities ahead of the daily minimum reading.