NEW YORK (CNN/Money) - The Nasdaq is enjoying its strongest September since 1999, the Dow and S&P are seeing their best since 1998. But Wall Streeters, used to selloffs and crashes this time of the year, are still skeptical about the market's ability to keep climbing through October.

"You always hear that September and October are bad months for the stock market, especially October," said Bill Roe, portfolio manager at Melhado Flynn & Associates. "I think there's a lot of caution. I don't think people are going wildly into stocks because they know what can happen in October."

Caution aside, the Nasdaq composite index claimed gains of 4.3 percent in the first five trading days this month -- its second best early-September run in the past 15 years, according to the Hirsch Organization, publishers of the Stock Traders Almanac. The Nasdaq gained 2 percent over the first two weeks of the month.

The Dow jumped 0.4 percent, and the S&P 0.7 percent -- much better than their averages over the past 15 years for the first 10 trading days of the month. This is the kind of performance Wall Street hasn't seen in years.

Thanks to the market crashes of 1929 and 1987, as well as the wild rides of the late 1990s, October has the reputation of being a "jinx month" for the market. But it can also be a turnaround month for stocks -- it was that in 1998 and 1999. Despite significant drops at the beginning of October in those years, stocks managed to end the month with big gains.

With the economy on the rebound and the market on a bull ride since March, stocks are likely to take their cue from the third-quarter earnings reports that are set to start rolling in mid-October. And the earnings season is expected to be strong. Already, the number of companies upwardly revising their guidance has grown 27 percent from the same period last year.

"There's no doubt that earnings are going to be better, said Jon Burnham, portfolio manager at Burnham Securities.

Investors got their first taste of corporate America's bottom line performance when a handful of financial services companies began posting their results Thursday. Despite their exposure to rising interest rates, five of Wall Street's heavyweights due to report in the coming days are expected to post stellar results.

Bear Stearns (BSC: Research, Estimates) and A.G. Edwards (AGE: Research, Estimates) each reported quarterly earnings Thursday morning that soared past Wall Street's estimates. Bear Stearns' bottom line was helped especially by its thriving bond business, even in the face of rising rates.

If Goldman Sachs (GS: Research, Estimates), Lehman Brothers (LEH: Research, Estimates) and Morgan Stanley (MWD: Research, Estimates), due Tuesday, also deliver on the expectations, the entire financial sector and the broader stock market could celebrate by moving higher still.

"A lot of people were concerned about how the back-up in interest rates was going to affect these companies," said Reilly Tierney, financial analyst at Fox, Pitt Kelton. "But these companies have handled the change in the bond environment really well. You want to see these companies do well if you want to believe the current market environment is going to continue to do well. These are leading indicator-type stocks."

The third quarter may have been a strong one for investment companies, but banks with large mortgage businesses probably got stung by the late summer rise in interest rates. Two of the top three mortgage lenders, Washington Mutual (WM: Research, Estimates) and Countrywide Financial (CFC: Research, Estimates) warned Tuesday that they suffered large declines in mortgage applications in August from the prior month. Washington Mutual said it would take a loss for the sale of mortgages in the third quarter. Countrywide Financial is set to report quarterly results on Oct. 21, while Washington Mutual's report is due on Oct. 14.

Despite Wall Street's interest rate anxiety, the Federal Reserve's stated commitment to keep rates low, reiterated in comments after its last policy meeting Tuesday, also has the potential to keep optimism up in October. Add to that economists' projections that the economy will grow at a rate of 4.5 percent in the third quarter, from 2.4 percent in the second quarter and the basis could be there for an unusually strong and smooth October for stocks.

Yet, many market watchers are still wary. As of Wednesday's close, the Dow had risen 14.7 percent so far this year and the S&P had gained 17 percent. The Nasdaq had jumped a whopping 41.3 percent.

This runup has some money managers nervous. They also worry about continued tensions in Iraq and the Middle East and a labor market that has yet to show signs of better health.

"October can be a difficult month, so I don't want to bet on October," Burnham said. "But I don't think it will be terrible."