In the past year, shares of Amazon (AMZN) - Get Report  , currently at $835, have risen 40%. The online retail behemoth reports fiscal third-quarter earnings after the close on Thursday. Can Amazon produce another blockbuster quarter or are things about to get cloudy?

Analysts are looking for third quarter revenue of $32.66 billion, up 28.9%, and earnings of 81 cents per share. North American revenue should be up 26% to $18.9 billion and international revenue of $10.5 billion will likely be up 28%.

Operating profit is expected to be at least $750 million on a 36% gross margin. The consensus is forecasting Ebitda of $3.4 billion.

The big driver of Amazon's results will be the company's cloud business, Amazon Web Services. I think investors should be concerned about a big AWS slowdown, especially with the stock up so much in the last year.

In the first quarter, AWS revenue grew 64%, then, in second quarter, 58.2% -- lower than the most optimistic forecast of 62%. This quarter AWS is projected to slow to 53%.

Investors may start to worry that AWS is up against impossibly tough comparisons. In last year's fourth quarter, AWS grew 69%. There's no way Amazon is going to beat that number.

I believe management will guide AWS fourth-quarter revenue growth in the high 40%, which would only highlight the dramatic loss of sales momentum at Amazon Web Services. While 47% to 49% sales growth is awesome, I think investors want more.

In fact, I think investors only really care about AWS and are ignoring the e-commerce side of the business. AWS profitability is driving earnings and the stock. Any slowdown at AWS is sure to throw a monkey wrench into investor's expectations.

I expect an in-line third quarter but I think things are going to get increasingly cloudy in the fourth quarter.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.