We're now into September, and that means many investors wonder if the September effect will be in place. This speaks to the historical trend of stocks underperforming in September compared to other months.  

How you approach September may depend on whether you're an optimist or a pessimist. Sorry, no “I'm a realist" answers will be accepted. If you're more pessimistic, you'll join many others who view September and October as months to sell stocks and look for the safety of other asset classes. 

But if you're an optimist, you may be willing to poke around at stocks, particularly from quality companies that may offer a buying opportunity. This isn't about being reckless; it's about being prudent. The best-in-class companies will continue to be solid investments regardless of what's happening in the economy at any given moment.  

Here are three growth stocks that offer investors a buying opportunity in September.  

Standing Out in a Tight Credit Market 

For more than a year, the canary in the recessionary coal mine has been the uncomfortable, if not record, level of consumer credit card debt. That has government regulators looking to force credit card issuers to lower the late fees they can charge to as low as $8 from their current level between $31 and $40.  

That's putting pressure on the stock of credit card issuers. However, analysts believe the American Express Company (NYSE: AXP) is better positioned to deal with this regulation. To be fair, many Amex cards allow consumers to carry balances. That wasn't always the case. Still, the company continues to cater to premium consumers who tend to have higher incomes.  

The takeaway is that the company relies less on late fees as part of its revenue stream. This can allow investors to focus on other fundamentals. That starts with earnings. The company posted mixed results in its July earnings report. But it beat on the bottom line and raised its forward guidance.  

American Express analyst ratings on MarketBeat give AXP stock an 8% upside. That would more than make up for the dip in the stock since the earnings report.  

Buy the Dip After Investors Sell the News  

Amgen, Inc. (NASDAQ: AMGN) has taken investors on a roller coaster ride over the last 12 months. AMGN stock is down sharply from its 52-week high and continues to fall since the news came out that the Federal Trade Commission (FTC) granted permission for the company to complete its $27.8 billion purchase of Horizon Therapeutics Public Limited Company (NASDAQ: HZNP).  

Primarily due to uncertainty surrounding the FTC's decision, there wasn't a lot of conviction with AMGN stock. Since the news broke, there have been slightly more put options than call options. That means the stock could move lower.  

However, Amgen is expected to increase earnings by 8% over the next year. Analysts may not fully appreciate that. However, on September 6, HSBC raised its price target for AMGN stock to $320, which is 25% higher than the current consensus price target.  

There's Still Time to Take a Bite Out of Apple 

Apple, Inc. (NASDAQ: AAPL) is up about 4.5% in the last month, but it's still below the highs of late July and early August. Is that enough growth to attract investors? It should, but not for the reasons you may think. 

Many investors are focusing on Apple's upcoming launch event on September 12. If you're a fan of Apple products, seeing what new products the company will roll out is always interesting. This year, consumers and investors will focus on the company's iPhone 15. 

I won't try to say that iPhone sales aren't important to Apple. But as many investors know, it's becoming a (slightly) smaller piece of the overall pie. The tech giant continues to grow its Wearables and Services business. And part of that includes Apple TV, which has captured about 6% of the streaming market.  

That's still a far cry from Netflix, Inc. (NASDAQ: NFLX), Amazon.com, Inc. (NASDAQ: AMZN) and even The Walt Disney Company (NYSE: DIS). But, at $6.99 per month, the service offers great value and continues to expand into areas like live sports, which may make it more compelling.  

Traders are likely to continue shorting AAPL stock. It's one of the most heavily shorted stocks. But now is a good time to consider nibbling on the stock if you have a long position. The Apple analyst ratings on MarketBeat give the stock a consensus price target of $198.86, which is 5.5% higher than its current price. However, several analysts are giving Apple much higher price targets.