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Christmas came early for Amazon, time to sell?

A screen showing Black Friday deals on Amazon.com
Source: Amazon.com
A screen showing Black Friday deals on Amazon.com

You could set Santa's watch to this pattern. Every year that Amazon's stock rises before Thanksgiving in anticipation of a strong holiday season, the shares tread water the rest of the year, recent history shows.

So with Amazon up 16 percent from a 52-week low in October, a strong holiday shopping season may already be priced in.

Over the last 10 years, Amazon on five occasions has traded higher the month before the Black Friday-Cyber Monday start to the shopping season. On all five of those occasions, the stock trailed the S&P 500 through the end of the year. For those five instances, the stock had a median gain of 19.67 percent in the 30 trading days before Thanksgiving and a median loss of 2 percent in the 30 days that followed, according to Kensho, a powerful analytics tool used by hedge funds.

"What we've seen over the last couple years is that growth is stronger in the earlier part of the holiday—Thanksgiving, Black Friday," said Aaron Kessler, senior research analyst at Raymond James, which has a "hold" rating on the stock.

"I think consumers are buying earlier and earlier each year," he said. "Companies are also offering their deals earlier."

Kessler pointed out that Amazon has already released its deals for Black Friday shoppers, about a week earlier than usual.

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So as the shoppers come to Amazon earlier and earlier, so do the investors.

Just how good will the holidays be for Amazon? Analysts polled by Reuters expect fourth-quarter sales of $29.75 billion for the company, an increase of 16 percent from the same quarter last year.

To be sure, Amazon is trying to buck this seasonal trend and keep the good cheer flowing throughout the whole year. Bezos & Co. are doing that by strategically announcing buzzworthy products and strategic partnerships to draw eyeballs to the website.

For example, last quarter Amazon announced unlimited cloud photo storage for Prime users, grocery delivery service in Brooklyn and the purchase of live-video gaming platform, Twitch. Earlier this month, It turned heads on social platforms with the announcement of Echo, a talking personal assistant contained in a single desk speaker.

"The investments continue to lead to site traffic growth," said R.J. Hottovy of Morningstar, which has a "buy" rating on the stock.

And the tack-ons to its Prime services continue to "give customers less reason to shop elsewhere," the analyst said.

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CNBC's parent NBCUniversal is a minority investor in Kensho.

Correction: This version corrected to indicate that for the five instances in question, the stock had a median gain of 19.67 percent in the 30 days before Thanksgiving and a median loss of 2 percent in the 30 days that followed.