In August, I wrote an article for Barchart about a 75-day seasonal selling window in December Euro FX futures, asking whether traders were prepared for the potential decline. That pattern now deserves renewed attention. Additional 15-year seasonal studies show that several other U.S. dollar-paired currencies have historically weakened during the September window: December Swiss franc and New Zealand dollar futures declined in 14 of the past 15 years, while December Euro FX, British Pound, and Japanese yen futures declined in all 15. Those percentages—93% and 100%, respectively—describe historical consistency, not certainty, and a 15-year sample should never be mistaken for a guaranteed outcome. Nevertheless, when several independently traded currencies begin to exhibit comparable seasonal behavior against the same counter currency, the common denominator matters. In this case, that denominator is potential U.S. dollar strength. Seasonality identifies the window, but the trade still requires confirmation from price structure, momentum, and risk parameters appropriate to current volatility.
Global Interest Rates
The interest-rate backdrop provides a credible fundamental tailwind for that seasonal tendency. However, the policy picture is more nuanced than simply describing the Federal Reserve as hawkish and everyone else as dovish. As of early September, the Fed’s target range stands at 3.50%–3.75%; July’s FOMC minutes described economic growth as solid and inflation as remaining above the 2% objective. The ECB has also tightened, raising its deposit rate to 2.25% in June before holding steady in July, while the Bank of Japan has moved its policy rate to 1%. Even after those adjustments, however, U.S. short-term rates remain appreciably above comparable policy rates in the euro area and Japan. That differential can support the dollar through carry demand and the relative appeal of dollar-denominated fixed-income assets. Traders should recognize the counterargument: additional ECB or BOJ tightening, particularly a faster-than-expected normalization in Japan, could narrow that advantage. For now, persistent U.S. inflation and resilient activity leave the Fed less room to ease aggressively, preserving a fundamental backdrop consistent with seasonal dollar strength.















