S&P 500 Gains Over 2% in August; September Seasonal Weakness Looms Again
nashnova research
The S&P 500 gained over 2% in August while the Dow hit multiple all-time highs, but September — historically the worst month for US stocks — is approaching with seasonal headwinds, technical warnings, and overheated sentiment converging, prompting multiple firms to turn cautious.
Why is September called the weakest month?
Per the 2026 *Stock Trader's Almanac*, since 1950 the Dow has averaged a 0.8% September decline and the S&P 500 a 0.7% drop; the Nasdaq has averaged −0.9% since 1971 and the Russell 2000 −0.8% since 1979.
This means → September is the only month where large-caps, small-caps, and tech all post negative averages.
The Almanac's explanation: fund managers return after Labor Day and dump positions, then quarter-end mutual-fund rebalancing drags down the final weeks — in 18 of the past 30 years the S&P started September strong but gave it back by month-end.
What does midterm-election-year rotation add to the risk?
Roth Capital chief technical strategist JC O'Hara notes that midterm-election years historically bring sharper volatility in September and October; money is currently rotating into first-half laggards. This reflects a defensive repositioning ahead of autumn.
BTIG chief market technician Jonathan Krinsky warns that the recent rotation is just capital "sloshing back and forth" between sectors without building upward momentum. In plain terms = the money hasn't left, but it's not pushing in one direction — so the index stalls.
He adds: if capital that exited AI and tech stocks fails to return, the market could face a fresh leg down.
What are the technical warning signals?
JPMorgan technical strategist Jason Hunter flags that the S&P 500 is approaching long-term channel resistance near 7,900, while AI-linked stocks remain weak.
The Philadelphia Semiconductor Index broke key support in June and still sits roughly 22% below its all-time peak, with limited rebound strength. This means → the semiconductor correction may not be over yet.
Hunter adds a caveat: the past 18–24 months show that front-running a downturn has not been a profitable strategy. In plain terms = the signals are real, but the people who shorted early didn't make money either.
How overheated is sentiment?
Ned Davis Research analyst London Stockton notes that the firm's crowd-sentiment and trading-sentiment gauges are both in the "excessive optimism" zone. Historically, when both hit that level simultaneously, markets tend to come under pressure.
Stockton suggests the market may need a period of choppiness to digest the optimism — or simply wait until midterm-election uncertainty clears.
Some investors treat the S&P 500 equal-weight index as a safer bet — it sits only ~1% off its high. But BTIG data show that in every midterm-election year since 1990, the equal-weight index suffered at least a 7% pullback between August and October (the sole exception, 2006, had already dropped 9% from May to July). In plain terms = equal-weight looks diversified, but historically it can't dodge this window either.
Can fundamentals hold the line?
August's rally rested on strong earnings: US pre-tax corporate profits jumped to $4.8 trillion in Q2, or 18% of national income — the highest share on record since at least 1950.
Nvidia beat Q2 expectations, but also disclosed a sharp rise in receivables and a corresponding drop in free cash flow. This means → the revenue headline looks great, but cash collection is slowing — quality bears watching.
Macro variables are stacking up too: the PCE price index rose 3.7% year-over-year, nearly double the Fed's 2% target; WTI crude hit $86.79 per barrel on Monday, its highest since August 21; and the US and Iran exchanged strikes for the first time in over a month, escalating geopolitical tension.
What is September's real test?
Seasonal pressure, technical resistance, overheated sentiment, and geopolitical risk are converging on four fronts — that is the full risk map September faces.
Over the past two years, the market has repeatedly shown "counter-seasonal" resilience, bouncing back every time bears called a top. This reflects underlying support from earnings fundamentals and capital flows.
In plain terms = the real question for September isn't "will it drop?" — it's whether the resilience that defied history before can survive all four pressures arriving at once.
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