TOKYO: Investors have fallen over each other in recent weeks to buy the yen on bets that interest rates are finally about to tip in Japan’s favour.

They face a moment of truth as soon as Wednesday.

The currency has climbed roughly 5% against the dollar since it began surging on July 11, a move that was amplified by suspected market intervention from Japanese authorities.

After vacillating between gains and losses in Tokyo and London trading last Friday, the yen rallied as much as 0.5% in New York before paring the advance.

But some investors warn that the rally is fragile, as was on show last week when the yen rapidly retraced an advance after last Thursday’s stronger-than-expected US economic growth figures.

Swaps markets suggest a roughly 45% chance of the Bank of Japan (BoJ) hiking rates by 15 basis points at the conclusion of its July 31 policy meeting, indicating plenty of caution.

And only 30% of BoJ watchers surveyed by Bloomberg forecast a hike, even if more than 90% see it as a risk.

That leaves yen bulls vulnerable, particularly if the BoJ also disappoints on expectations for a sizeable cut in bond purchases, or if the Federal Reserve later in the day does anything to dampen hopes for a rate cut in September.

“This is a crazy yen rally,” said Nick Twidale of ATFX Global Markets, who has traded Japan’s currency for a quarter of a century. “The BoJ could be party poopers and not play its part in tightening policy.”

Twidale said that if the BoJ underwhelms the market, carry trades that have kept the yen weak “may come back with a vengeance”.

Others from BlackRock Inc to former central-bank officials are predicting the BoJ will stand pat on interest rates for longer.

Patchy economic data lend credence to this view: While a key gauge tracking the strength of Japan’s service sector rebounded in July, a measure of factory activity showed a contraction.

Weak consumer spending is further complicating the BoJ’s decision next week, people familiar with the matter said.

“If the BoJ does nothing, the dollar-yen rate could surge again,” said Amir Anvarzadeh, strategist at Asymmetric Advisors who has tracked Japanese markets for over three decades.

The yen traded 0.1% higher to 153.75 per dollar at 3.30pm in New York. Inflation figures for Tokyo earlier showed that consumer prices accelerated for a third month.

Nathan Swami, head of foreign-exchange trading for Asia Pacific at Citigroup Inc in Singapore, saw additional demand for bullish yen options after the outsized move this week.

“It is still too early to tell if this signals a longer-term investor sentiment shift, and may thus more likely be a tactical shift in short-term positioning or hedging activities for now,” he said.

According to other traders, some hedge funds remained on the sidelines amid uncertainty over how much the currency could gain ahead of next week’s BoJ policy meeting.

Still, many traders have slashed bearish yen bets in recent weeks.

Non-commercial traders - a group that includes hedge funds, asset managers and other speculative market players - now hold some US$8.9bil in positions tied to wagers that the yen will fall, according to the latest Commodity Futures Trading Commission data through July 23.

That’s the least short since mid-March and down from a near-term peak of more than US$14bil in early July.

If the BoJ “doesn’t fully deliver,” then the yen could weaken toward the 158 level against the dollar, according to National Australia Bank Ltd’s Rodrigo Catril.

Yet even if the BoJ does tighten policy on Wednesday, there is still a case for it to retain favour in carry trades, in which investors take advantage of Japan’s ultra-low interest rates to borrow in yen to then invest in currencies with higher yields.

 -Bloomberg