By Mike Dolan

LONDON (Reuters) - Investors have been braced for a stormy September for so long now it's getting difficult to see this month's stiffening gales blowing them off course for long.

September - traditionally the worst month of the year for U.S. stocks with an average loss since 1928 of 1.1 percent - does look rough again. It's just a wonder who's left to surprise.

Even a cursory glance at event diaries during the Spring would already have given fair warning of what the final month of the third quarter was brewing.

And markets have for months been shaping up for the first reduction of the U.S. Federal Reserve's bond buying program, or 'quantitative easing' on the 18th - with QE-buffeted emerging markets feeling the sharpest adjustment. German elections four days later could bring unfinished euro zone business - such as unresolved Greek bailout funding - back to the policy table.

U.S. budget wrangling also is set to resurface through the month as the Federal debt ceiling needs to be raised by mid-October to avoid default. And a possible U.S.-led strike on Syria, with all its potential impact on regional stability and world energy prices, emerged last month as a wild card.

But after several weeks mulling outcomes, postponing debt and equity issuance, hedging bets and diversifying portfolios, can there be any investors left unawares, and how much of all this is accounted for in prices?

Implied volatility gauges have popped higher (.VIX) (.V1XI), though only just back to June levels under 20 percent for Wall Street stocks and only slightly above long-term averages.

And aside from selected hard-hit emerging markets and currencies, such as Turkish stocks and India's rupee, most other major equity and bond markets have had less than 3 percent of froth blown away over the past two weeks.

Yet, the relatively limited if choppy August moves mask a much bigger global markets adjustment since May, when Fed 'tapering' was first mooted and ripped through many assets.

Perhaps the best illustration of that is the rise in investment fund cash holdings to their highest levels in 12 months in August, according to Reuters asset allocation polls.

Is that enough? The key question is whether the dominant Fed event has been finally discounted.

TAPER TIME

Strategists at Morgan Stanley believe it probably is, estimating that many of battered emerging debt markets are already priced as if 10-year U.S. Treasury yields were as high as 3.2 percent - some 30 basis points above current levels.

Reassured by evidence the United States, Britain, the euro zone and Japan have assumed 'global growth leadership' from flagging emerging world, as well as reduced anxiety about China's slowdown, the U.S. bank feels investors are already sufficiently strapped in for this month's bumpy ride.