Uh-Oh! The Latest September Inflation Forecast Spells Trouble for Wall Street, and It's Not Just Energy Prices to Blame.

On Sept. 16, for only the fourth time this century, the Federal Reserve kicked off a rate-hiking cycle. Fed Chair Kevin Warsh and his colleagues had little choice but to tackle persistently elevated inflation -- 66 months above the Fed's long-term target of 2% (and counting) -- head-on. The Federal Open Market Committee (FOMC) raised the federal funds target rate by 25 basis points to 3.75%-4.00%.

Unfortunately, inflationary pressures are far from over, and that's potentially terrible news for Wall Street and its major stock indexes, the Dow Jones Industrial Average (DJINDICES:^DJI), S&P 500 (SNPINDEX:^GSPC), and Nasdaq Composite (NASDAQINDEX:^IXIC).

Fed Chair Kevin Warsh and his colleagues may be just getting started in their fight against inflation. Image source: Official Federal Reserve Photo.

The latest September inflation update offers a worrisome outlook

Even though the September inflation data won't be released until Oct. 14, the Federal Reserve Bank of Cleveland's proprietary Inflation Nowcasting tool provides updated projections after the release of relevant economic data. As of the latest update on Sept. 25, things appear to be worsening.

Headline inflation for August clocked in at 3.4%, according to the U.S. Bureau of Labor Statistics. However, the Cleveland Fed expects the Consumer Price Index (CPI) to jump to 3.57% on an annualized basis in September.

BREAKING: US July PCE inflation, the Fed's preferred inflation metric, hits 3.7%, above expectations of 3.6%.

Core PCE inflation was 3.3%, the second highest reading since October 2024.

US inflation continues to run at nearly double the Fed's 2.0% target.

Own assets or be left…

— The Kobeissi Letter (@KobeissiLetter) August 26, 2026

It's an even direr outlook for Personal Consumption Expenditures (PCE), one of the central bank's preferred inflation measures. PCE accounts for the substitution effect (i.e., consumers trading down to cheaper goods) and includes third-party payments made on behalf of consumers. This makes it a more encompassing inflationary measure than the CPI.

The Inflation Nowcasting tool is forecasting an annualized PCE of 3.78% in August and 3.97% in September, up from a reported 3.7% in July.

Image source: Getty Images.

News flash: Energy isn't the only driver of inflation

The lion's share of this elevated inflation can be traced to President Donald Trump's policies. More specifically, the Iran war.

Since fighting commenced seven months ago, the near-persistent closure of the Strait of Hormuz has stymied the daily flow of approximately 20 million barrels of petroleum liquids. The largest energy supply disruption in modern history has sent gas and diesel prices soaring.

However, the Iran war isn't just an energy issue any longer. As Trumpflation (inflation specifically driven by Trump's policies) has evolved, so have the impacts of Iran-war-driven inflation.

For example, businesses have been forced to alter their modes of transportation, change shipping routes, alter their suppliers, and pay more for petroleum-based goods, such as plastics, due to the closure of the Strait of Hormuz. These added costs, plus several others not mentioned, have reached the broader economy and are directly impacting consumers' wallets.

The Fed’s preferred inflation gauge, Core PCE, came in at 3.3% for July.

That marks 65 consecutive months above the Fed’s 2% target.

In June, Kevin Warsh said:

“We’ve missed for 5 years. And we’re gonna fix that.”

So far: all talk, no action.

Video: https://t.co/9oZTwtA7vK pic.twitter.com/D5q3QLAEI1

— Charlie Bilello (@charliebilello) August 26, 2026

According to the Cleveland Fed, Core PCE, which excludes volatile food and energy costs, is expected to tick up from a reported 3.3% in July to an estimated 3.4% in August and 3.49% in September.

As Trumpflation digs in its heels, Fed Chair Warsh and the FOMC are likely to get more aggressive with interest-rate hikes. That's bad news for Wall Street.

Over the last four years, artificial intelligence (AI) has lifted the Dow Jones Industrial Average, S&P 500, and Nasdaq Composite to new heights. If the cost to finance the AI infrastructure build-out rises as the FOMC hikes rates, it could reduce AI growth expectations and force investors to rethink the otherworldly valuations bestowed on AI stocks.

Sean Williams has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.