In the foreign exchange market on Monday, the yen staged a significant rebound against the U.S. dollar, touching an intraday high of 154.04 yen per dollar, its highest level since February this year. During the London trading session, the yen even saw a rapid surge in just five minutes, with its single-day gain reaching 1.4% at one point. By the end of the trading day, the USD/JPY exchange rate closed down 1.2%, dropping 190 basis points to 154.34. This strong performance has led the yen to appreciate by a cumulative 3.4% over the first five trading days of early September, signaling a potential trend reversal after a prolonged period of depreciation.

The market widely speculates that this sharp rise in the yen may be linked to official Japanese intervention to support the currency during the U.S. Labor Day holiday, a period typically characterized by low liquidity. Previously, Japanese authorities had deployed a total of approximately 15.4 trillion yen (equivalent to $99.6 billion) for large-scale forex intervention in July and August. Against the backdrop of shrinking trading volumes during the holiday, the unusually massive transaction size observed during the session further fueled speculation about another round of official intervention, keeping many market participants highly alert to intervention risks.

In addition to potential forex intervention, the future monetary policy path of the Bank of Japan is also a core driver behind the yen's strength. Currently, the market prices in an 80% probability of the BOJ raising borrowing costs by 25 basis points to 1.25% at its meeting next week. Some even suggest that to combat inflationary pressures, the BOJ might hike rates again in October, resulting in the rare scenario of consecutive rate hikes. This shift in policy expectations has made some short-term funds nervous, triggering severe volatility in the forex market. However, some investors remain skeptical about the BOJ's resolve to maintain a sustained hawkish stance, believing that the subsequent policy direction still holds uncertainties.

The rapid appreciation of the yen has once again triggered market sensitivities regarding the large-scale unwinding of yen carry trades. Looking back at the summer of 2024, the BOJ's rate hike led to a reversal of carry trades, causing severe tremors across global financial markets. Data shows that the outstanding balance of cross-border yen borrowing has surged from 216 trillion yen at the end of 2021 to 360 trillion yen by March this year, an increase of two-thirds, marking the largest accumulation cycle of carry trades in the past 30 years. Facing such a massive scale of funds, the BOJ will inevitably need to balance the pace of rate hikes with financial market stability as it advances the normalization of its monetary policy.