September Market Weakness: The Setup Has Teeth

September weakness may not be a fluke, according to a market analysis citing Citadel Securities’ Scott Rubner. The piece points out that since 1928, September is the only month that closes lower more often than higher, with an average return around -1.1% and closer to -1.5% in midterm election years. It highlights that the back half of the month is historically the weakest two-week period, with typical intra-month selloffs averaging -4.7% (about -6.2% in midterms). The author argues that this year’s demand backdrop is also shifting: cohorts that fueled August’s S&P 500 highs are stepping back, and buybacks authorized for over $1.1 trillion through August could slow into early September as blackout periods accelerate around Sept. 12.