What is really supporting the dollar: rate differentials and positioning

Rate differentials: the direct source of dollar strength

The dollar index closed at 102.53 on 14 October, an 18-month high. The direct driver is the rate differential. US September CPI rose 3.7% year on year and 0.6% month on month, both above expectations, pushing the cumulative probability of one more Fed hike before year-end above 85%. Front-end Treasury yields rose accordingly, reinforcing the dollar's rate advantage.

The most direct gauge of the differential is the gap between the two-year Treasury yield and the two-year yield of the counterparty currency. When the gap widens, the dollar gains support. When it narrows, that support fades.

Risk sentiment: safe-haven and liquidity demand

The dollar is both a safe haven and the global settlement currency. When geopolitical risk rises — for example, Middle East supply disruption concerns pushing oil higher — demand for dollar liquidity increases, providing a second layer of support. That layer usually lasts less long than the rate differential, but it matters more during an event shock.

Positioning: the main source of short-term volatility

When the market forms a consensus about direction, positioning concentrates on one side. Even with no change in fundamentals, the unwinding of crowded positioning can produce substantial volatility. The usual way to observe positioning is through non-commercial net positions in the futures market and risk reversals in major currency options.

Note that positioning data is a lagging indicator. Its value lies in identifying the state of crowding, not in forecasting next week's move.

How the three variables combine

A workable framework: when the differential widens and positioning is not crowded, the probability of trend continuation is relatively high. When the differential widens but positioning is crowded, watch for a periodic pullback. When the differential narrows while positioning is crowded, that is the combination in which dollar longs most need to reduce.

What would change the current view

Three developments are worth watching: a sustained weakening in US employment data, a decline in inflation expectations, and a shift in Fed officials' language. Take September payrolls: 29,000 jobs added against a 90,000 forecast, yet a single month is not enough to change the path — repricing requires weakness that is consecutive and broad.