NEW YORK (CNN/Money) - Renowned rally killer August is on the move and its partner in crime, September, is just around the corner. So why aren't more market watchers panicking?

Maybe that's because they suspect that while a storm is definitely brewing, it may not turn into quite as torrential a flood as it has in recent years. Ah, the bulls. You've gotta love that optimism.

But don't get too excited, Pollyanna. Over the last 15 years, August has been the worst month for the Dow industrials and the S&P 500, while September has been the second worst, according to the Hirsch Organization, publishers of the Stock Trader's Almanac. For the Nasdaq, things are reversed. September is the worst, while August is the second worst. (See chart for more details.)

If you look back a little more, from the start of Nasdaq trade in 1971 through now, September has been the worst month for all three indexes and August the second-worst month.

Overall, in comparing the seasons, the old adage "spring ahead, fall back" takes on a new meaning. Fall as a whole has been pretty historically wretched. Since 1964, there have been 16 fall declines of more than 10 percent.

"The fall has traditionally caused anxiety for investors and produced some big declines, particularly in late August and early September," said Michael Sheldon, chief market strategist at Spencer Clarke.

"We're likely to see a correction this year after the run we've had, as well," Sheldon added. "But the outlook for third and fourth quarter earnings has been good, and if the economic data continue to improve, we could see a slightly more narrow decline that what people have been expecting."

In the period of August-October of 2001, the stock market lost 16.2 percent year-over-year, according to the Almanac; in 2002, it lost 19.5 percent year-over-year in the period.

"I'm not looking for quite the same steep declines this year, but early August has already been weak and we are definitely trending a lot lower for the period," said Jeffrey Hirsch, editor of the Stock Trader's Almanac. "You're not likely to see another sustained upturn until the end of the year."

But a silver lining, of sorts, does loom.

Major stock market crashes have given October the unsavory reputation as being something of a "jinx month," and it is historically pretty terrible, particularly for the Nasdaq. But October is actually not quite as terrible as people think it is, said Hirsch. The Almanac refers to it as the "bear killer," because although the first part of the month is usually pretty awful, often bear markets start to turn by the end of the month.

Since bottoming March 11, stocks have been on a tear. As of Friday's close, the Dow was up 21.6 percent, the S&P 500 was up 22.4 percent, and the Nasdaq composite was up 34.9 percent. But those gains were mostly accrued in the 3-1/2 months since the 2003 bottom, with investors betting on a second-half pickup and putting their money where their mouths were. For the last five weeks, stocks have been drifting in a range, as investors have sorted through second-quarter earnings and June and July economic figures.

"I think it's going to continue to be a sideways market in August and into September," said Peter Green, market analyst at MKM Partners. "Seasonally, there's the tendency for selling, but as of now, there aren't any big events on tap that could take us a lot higher or a lot lower."

The second-quarter earnings period is mostly done, with around 412 of the S&P 500 companies already having reported their results as of late Friday. So far, approximately 63.8 percent of reported earnings have beat estimates, 22.4 percent have met estimates, and 13.6 have missed. Traditionally, this time of year tends to be sluggish because once the bulk of second-quarter earnings is over with, the only consistent news coming in tends to be economic, and even that is muted in the face of weak summer volume. As a result, stocks tend to drift lower.

While that tendency is still there, "the one positive for the market this year is the monetary and fiscal stimulus that is in the pipeline," said Brett Gallagher, head of U.S. equities at Julius Baer. "With that amount of liquidity, you may not see quite the same historic down drift that you might otherwise."

"Our general view is that the market is very overbought and will go down, but that could be delayed somewhat," Gallagher added. "In the very near term, I hesitate to bet against the market when you've got this much stimulus."