September Seasonal Weakness Puts Micron, Nvidia and Broader Market on Watch as Rosh Hashanah Adage Returns

September has historically been the worst month for the S&P 500, and heading into September 2026, analysts and strategists are revisiting two overlapping seasonal signals: 98 years of data showing negative average returns for the index during the month, and the old Wall Street adage to sell on Rosh Hashanah and buy on Yom Kippur. MarketWatch and Nasdaq commentary published on September 3 highlighted both patterns as actionable frameworks for the current environment.

Micron Technology and Nvidia are receiving particular attention within this seasonal narrative. Micron is scheduled to report fiscal fourth-quarter 2026 earnings on September 30, squarely inside the historically weakest stretch of the year. The Federal Reserve's next rate decision, set for September 16, adds another variable: market pricing has shifted to a greater than 60% probability of a rate hike, up from 41.4% the prior week, following hawkish comments from Fed Chair Kevin Warsh at Jackson Hole. Analysts note that the rate decision could move Micron more than its own earnings report, given the company's sensitivity to borrowing costs and memory-cycle dynamics tied to AI infrastructure demand.

Among individual stocks outperforming the broader tape on September 3, Paccar, Arch Capital Group, and ATI all closed ahead of the S&P 500. The Rosh Hashanah sell signal, historically associated with only modest declines before Yom Kippur, is viewed by strategists as more a reflection of broader September seasonality than a stand-alone catalyst.