Now comes August

The Dow Jones Industrial Average ($INDU) had its best monthly performance -- up 8.6% -- since October 2002 and its best July since 1989.

The Standard & Poor's 500 Index ($INX) and the Nasdaq Composite Index ($COMPX) were up 7.4% and 7.8%, respectively -- their best July performances since 1997.

Now comes August, which can be a problematic month, which is followed by the always dangerous September. Since 1987, August has been one of the stock market's weakest months of the year, the Stock Trader Almanac says. August also typically sees low volume as many traders and investment professionals go on vacation.

August 2008, however, was benign: The Dow was up 1.5%, with the S&P 500 up 1.2% and the Nasdaq up 1.8%. But the market literally crashed in September 2008.