Now that worked out just swell, didn't it?

Remember way back on Sept. 15, when Japan intervened in the currency markets to drive down the soaring yen? The yen had just stormed through the 83-yen-to-the-dollar level that a number of large Japanese exporters had pegged as the exchange rate where they stopped making money.

By buying U.S. dollars and selling yen, the intervention succeeded in driving the yen down to an exchange rate of 86 to the dollar.

Temporarily.

By Oct. 6, the yen had climbed back to the exchange rate that prevailed before Japan intervened -- and then some. The yen closed Monday at 82.70 to the U.S. dollar.

It's likely that the yen will keep climbing, too -- even if fears that the Bank of Japan will intervene again restrains the rate of that climb. On Monday, the yen, which had strengthened to 81.36 to the dollar, fell back to 82.70 on fears that the Bank of Japan would move.

Currency traders have been loading up on short positions against the dollar. They know they're exposed because of the size of those positions, and that makes them nervous. And as I've written a number of times recently, the dollar is so oversold that a short-term bounce is looking increasingly likely. (For more, see my post).

But most currency traders believe they've got weeks yet before the Japanese government intervenes again. They say that the Japanese government won't intervene to weaken the yen until after the G20 meeting in Seoul that ends on Nov. 12. Intervening before a meeting where currency interventions will be a hot topic would be just too provocative and would expose Japan to renewed criticism that its intervention has stoked an already-worrisome currency war.

That's even though smaller Asian countries such as Thailand, Taiwan, Malaysia, the Philippines, and even host-nation South Korea look like they intervened in the currency markets last week.

But with the yen hitting a new15-year high against the dollar, I expect Japan to intervene after the meeting ends unless G20 officials can cobble together a deal with China to allow the renminbi to appreciate. And with China signaling its reluctance to even discuss a deal, the odds are very low that the G20 meeting will yield anything that would be definite enough to head off another Japanese intervention to weaken the yen.

Full disclosure: At the time of this writing, Jim Jubak didn't own shares of any company mentioned in this post in his personal portfolio.