Stocks tend to plummet in September - but expect a better month this year, Bank of America says

• The S&P 500 tends to perform badly in September, sliding 0.7% on average.
• But it could buck that trend this month, according to Bank of America.
• The benchmark index's 18% rally year-to-date has set it up for further gains, one strategist said.

Stocks are one trading session into what's historically been their worst overall month. 

Since 1945, the S&P 500 has slid 0.7% on average in September, data from CFRA Research shows.