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The truth about 'September swoons': Strategist

Canaccord's Dwyer: Don't sweat September
Canaccord's Dwyer: Don't sweat September

It's the latest calendar-based worry for investors: That the historically tricky month of September could bring trouble for stocks in 2014. But while the long-term historical metrics make the beginning of autumn look dangerous, Canaccord Genuity strategist Tony Dwyer says that concerns about the month are a bit overblown.

First of all, Dwyer grants that September may bring some trouble. Using data from SentimenTrader, he points out going back to 1929, in the 12 times that the S&P has risen more than 3 percent in August to hit a 52-week high (precisely the situation in the prior month) September has only been positive once. That means it's been a down month 92 percent of the time.

Read More Why analysts say September could be a big deal

However, the median loss in those situations has been a mere 1 percent, he adds. And even that number is "highly skewed" by massive losses in the Great Depression and in 1987.

And while suggesting that September could bring rockiness, Dwyer maintains a very bullish perspective on stocks as a whole.

"If the market gods give you a gift of weakness, with the fundamental and tactical backdrop that we have, I think you want to be adding to your core position in equities," he said Tuesday on CNBC's "Futures Now."

Read MoreHot August may give way to cool September

Traders on the floor of the New York Stock Exchange.
Lucas Jackson | Reuters

And even short-term traders might not want to step in the way of the rally.

September swoons could be "a reflection of a very strong August—people come back to work and say, 'OK, maybe my number are a little bit too high,'" he said, when asked for a possible explanation of the market phenomenon. But "either way, it's not something you want to bet on, because it gets reversed in the fourth quarter."

Indeed, after a September drop, the markets tend to close the year higher—rising 75 percent of the time in the fourth quarter, for an average gain of 2 percent, Dwyer said.

—By CNBC's Alex Rosenberg

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