Seasonal Headwinds Meet AI Names: September’s Historical Weakness in Focus

September has long carried a reputation as one of the weakest months for U.S. equities, and a recent analysis highlighted the pattern’s depth: since 1928, the S&P 500 Index has declined by an average of 1.1% during the month. The weakness tends to be amplified in midterm election years — Cantor Fitzgerald data cited in the analysis shows the index has fallen 5% during the September–October window 15 times since 1930.

Investors watching this year’s seasonal stretch are also weighing macro pressures beyond the calendar, including geopolitical tensions in the Middle East and signs of strain among U.S. consumers. Against that backdrop, attention has turned to how artificial intelligence-linked stocks — many of which have driven market gains — weather a potential pullback.

How Three AI-Linked Names Are Trading

Marvell Technology stood out on Tuesday, with shares climbing 7.11% to $223.55 from a prior close of $208.70. The semiconductor company, which designs data infrastructure chips spanning the data center core to the network edge, carries a market capitalization of roughly $164.5 billion.

Palantir Technologies slipped 0.64% to $169.53, down from a previous close of $170.62. The software company, known for its Gotham platform used by intelligence communities in the U.S. and U.K., remains one of the larger names in the AI software space with a market cap near $407.4 billion.

Snowflake saw a sharper decline, falling 5.15% to $337.18 from $355.50. The cloud data platform provider, whose AI Data Cloud lets organizations consolidate data into a single source of truth, holds a market capitalization of approximately $114.5 billion.

The Seasonal Setup

The divergence in Tuesday’s moves illustrates how uneven AI-related trading can be even within a single session. Semiconductor and infrastructure names tied to data center buildouts have at times moved independently of software firms whose AI narratives are still maturing commercially.

Historical seasonal patterns are averages, not guarantees, and analysts typically caution that September’s weak track record reflects many different market environments across nearly a century. Still, with midterm-year dynamics and current macro pressures layered on top, the month arrives with more than the usual share of cautionary context for equity investors.

Source: original release

What to watch

• Upcoming quarterly earnings reports and guidance from Marvell, Palantir, and Snowflake, particularly any commentary on AI-related demand.
• Broad-market performance through September and October, given the historical midterm-year pattern cited by Cantor Fitzgerald.
• Developments in geopolitical tensions and U.S. consumer spending data that could add pressure to equity markets.