Traders returning from August breaks confront a concentrated set of risks that could drive volatility across asset classes in September. Market participants point to continued concern about elevated sovereign debt levels and the risk of more persistent inflation as key undercurrents. The following outlines the principal issues investors will be watching in the coming weeks.
1) Duration of the Iran conflict and its market consequences
The ongoing war with Iran has been a primary market mover, creating wide swings in oil and gas prices as investors attempt to gauge the likelihood and timing of reopened maritime routes, particularly the Strait of Hormuz. Those price moves have provided a tailwind for energy stocks while weighing on major energy-consuming industries. Higher energy costs have fed into inflation readings and pressured sovereign bond markets.
So far, global economic growth has absorbed much of the shock, but the near-term buffers that initially cushioned the impact are eroding. In the immediate term, diplomatic discussions between Iran and Oman focused on management of the Strait of Hormuz are the attention point. For investors with longer horizons, there is consideration of geopolitical and economic realignments, including the possibility of new pipeline routes that bypass Hormuz and the emergence of fresh regional partnerships, such as potential alignments involving Saudi Arabia, Pakistan and Turkey.
2) A pivotal week for major central banks
September brings simultaneous meetings of the U.S. Federal Reserve and the Bank of Japan, a scheduling overlap that could generate a concentrated burst of market volatility. Markets assign roughly a 40% probability to a Fed rate increase at the September 16 meeting, making both the action taken and the rhetoric around it significant. What Chair Kevin Warsh says at the Fed - including remarks he is due to deliver at the Jackson Hole symposium - will matter as much as any policy decision. Observers note that Warsh’s relatively reserved communication style has at times left markets unclear on the Fed’s intentions.
Complicating the Fed outlook is recent U.S. Treasury intervention in bond markets, which may dilute the market’s ability to price risks and thus muddle the Fed’s signaling. "How the Fed is going to communicate going forward is important because it impacts their overall credibility and global interest rates," said Justin Onuekwusi, chief investment officer at St. James’s Place.
In Japan, where authorities recently stepped in to support a stronger yen, markets are pricing in a Bank of Japan rate increase at its September 18 meeting. Market-watchers emphasize that central bank tone will be decisive - "It’s all about the narrative and how hawkish the governor sounds," said Hank Calenti, chief strategist for global markets at SMBC EMEA - with the potential to reshape Japan’s government bond yield curve. Ten-year Japanese yields are approaching 3%, the highest level seen since the mid-1990s.
3) The AI listings question and tech-market sensitivity
Investor enthusiasm around AI has been a major equity theme, and the prospect of a very large AI-focused initial public offering adds another layer of market risk. Anthropic is widely expected to be the next heavyweight tech company to go public following a blockbuster SpaceX listing in June; reports indicate it may seek to raise as much as $100 billion. Market participants warn that such an offering - with reported valuations that reached $965 billion in May and talk of a possible $1 trillion IPO valuation - could strain the AI trade as markets absorb substantial bond sales by big tech companies to finance capital spending.
Rory Dowie, multi-asset portfolio manager at Marlborough, expects valuations for Anthropic and OpenAI to be particularly frothy. Violeta Todorova, senior research analyst at Leverage Shares, pointed to the narrowness of investor exposure to the AI theme, noting that a sudden drop in appetite would reverberate through firms already priced for robust AI infrastructure demand - including major suppliers and cloud providers.
4) French fiscal tensions and broader euro-area politics
The French government is due to present a draft budget to the National Assembly in the coming weeks, setting up a contentious fiscal debate. Authorities intend to keep the deficit under control as they approach the 2027 presidential contest, an election that some polls suggest could benefit the far right. Zurich Insurance Group’s chief economist Guy Miller warned there is a risk of higher yields on OATs (French government bonds), though he does not expect movements large enough to threaten the overall euro-area debt framework.
Germany’s sovereign debt could face pressure as well amid a sequence of state elections that may weigh on Chancellor Friedrich Merz’s standing. Merz has seen his popularity dented by a series of political missteps, and some polls indicate the far-right AfD could outpace his party in certain state-level contests.
5) The new British government’s fiscal test
In the United Kingdom, Prime Minister Andy Burnham’s policy agenda has not yet unsettled markets markedly, but any attempt to lift growth while fiscal room is limited could alter that balance. The October budget and the Labour Party conference in September will be early opportunities to assess how the new administration and finance minister John Healey intend to reconcile growth objectives with constrained public finances. Ten-year UK borrowing costs remain elevated, although they have retreated from 18-year highs reached in May. The memory of the 2022 mini-budget crisis is likely to constrain policy choices; Burnham has indicated he will adhere to the UK’s fiscal rules. "There is a risk they try and push the envelope, and I think that would be a mistake," said Andrew Wishart, senior UK economist at Berenberg.
6) U.S. midterms, gas prices and political timing
September typically marks the start of an intensified campaign period ahead of the U.S. midterms in November, a dynamic that could influence economic policy and market sentiment. Consumers are watching gasoline prices, which have risen above $4 a gallon on average as a result of the Iran conflict, after being below $3 in January. President Donald Trump recently told Americans that higher prices were worth the cost of defeating Iran; some analysts believe the administration prefers gasoline prices to ease before voters head to the polls.
Jefferies’ chief European economist Mohit Kumar connects the political calendar to efforts by Treasury Secretary Scott Bessent to reduce borrowing costs. Kumar argues the administration has limited scope to tolerate higher long-term rates ahead of the midterms because mortgage costs are linked to the long end of the Treasury yield curve.
Collectively, these threads - geopolitics, central-bank communication, tech-related capital markets activity, European and UK fiscal politics, and the U.S. election timetable - form a dense backdrop for market participants returning to work. Each element carries the potential to shift asset pricing in bonds, currencies and equities, and investors will be parsing policy signals and political developments closely in the weeks ahead.