The temperatures are scorching on Wall Street, and so is the market. The has jumped 3.5 percent this month, placing the index on track for its best August since 2014, when it gained 3.8 percent.

Underscoring the market's performance is this week's historic run: The last time the S&P 500 achieved four consecutive highs during the month of August was in 1987, according to an LPL Financial analysis. Of course, that run preceded the "Black Monday" crash in October.

Now, some market watchers are forecasting a pullback in the coming weeks as stocks hit record highs.

"I'm skeptical that the S&P can continue this uninterrupted, and I do expect we'll see at least a 4 to 5 percent correction, at least sometime in the month of September into October," Mark Newton, founder and president of Newton Advisors, told CNBC's "Trading Nation" on Wednesday.

He's most cautious because September is traditionally a rocky time for the market, particularly during midterm election years, and the Dow and S&P 500 typically post losses. Newton also cited high investor sentiment and the fact that U.S. markets are so far ahead of foreign equity markets, which have taken a hit in recent months.

After getting knocked down earlier this year amid sharp declines in big tech and trade war-induced volatility, the broader market has clawed back its gains and all major indexes hover at or near record highs.

Newton said even though he's cautious in the near term, he isn't taking all his chips off the table.

"Anything down near 2,700 for me would be an excellent chance to take a look at buying," Newton said, adding that health care is his favorite sector to own into year-end. The group has been on a tear, rallying 11 percent as the top sector this quarter and coming out even atop high-flying technology stocks.

Other market strategists are similarly wary about buying stocks at these levels given September's usual bearish track record.

"I'd rather wait until that time passes before getting long the S&P. Any kind of a pullback, that would be a good time in November for us to get long," Boris Schlossberg, managing director of foreign exchange at BK Asset Management, said Wednesday on "Trading Nation."

Still, he isn't entirely pessimistic about the market; he's most bullish on the financials into year-end as he forecasts a steepening yield curve and continued rising inflation. He also cites the group's "oversold" condition as a reason to get bullish.

The broad U.S. equity markets closed out the session on Wednesday slightly higher, with the Dow posting its highest close since February and the S&P 500 posting an all-time high at 2,914.04.