Apple Watches, which Adobe predicts will be hot sellers this holiday season, are displayed at an Apple store in New York. (John Taggart/Bloomberg)

As millions of online shoppers swipe and tap their way down their Christmas shopping lists this year, two categories are forecast to account for the lion’s share of people’s projected $83 billion in spending: electronics and gift cards.

Based on an analysis of more than 1 trillion visits to retail Web sites, Adobe predicts that 76 percent of online sales during the holiday season will be rung up from just 1 percent of items.  Some 60 percent of those sales will be electronics, Adobe expects, and another 10 percent will be gift cards.

In other words, there is an intense concentration of shopper interest online around a very narrow array of products.  And Tamara Gaffney, Adobe Digital Index’s principal research analyst, says that while this is especially true during the holidays, the pattern holds all year long.  Even outside of November and December, Adobe finds that 65 percent of online sales go to 1 percent of items.

These findings underscore how unevenly the impact of e-commerce has been felt throughout the retail industry.  In the electronics category, where it is particularly easy to comparison shop online, consumers have been especially willing to pony up in the digital channel.  An iPad is the same whether I get it from Best Buy, the Apple store or Amazon, the reasoning seems to be, and so the purchase comes down to convenience and price. But other categories, such as jewelry and home goods, so far have been less affected by the rise of online shopping, perhaps a sign that shoppers still like to touch and test out these kinds of items before they spend on them.

Gaffney said the concentration of shopping dollars around such a thin slice of products means it is especially crucial for retailers to make wise inventory decisions this holiday season.

“It’s a time of year when, in reality, product variety is not going to win,” Gaffney said. Instead, she added, retailers can best position for the season by making sure they’re always in-stock on a few key items. 

Adobe’s models also shed light on the extent to which Black Friday is morphing from a one-day shopping sprint into a several days-long marathon that often doesn’t even involve a trip to the mall.  The company projects that online sales on Thanksgiving Day will total $1.6 billion; Black Friday, $2.7 billion; and Cyber Monday, $3 billion.  Thanksgiving Day is expected to be the fastest-growing shopping day, with an 18 percent increase in sales over last year.

If you’re a bargain hunter, the projections suggest that it’s best to get an early start on your shopping.  Adobe forecasts that prices on toys will actually be lowest on the Saturday before Thanksgiving, and for electronics, the Monday before Thanksgiving.  Procrastinating husbands and boyfriends, take note: Jewelry prices are predicted to be lowest on Thanksgiving Day.

And while we typically think of Black Friday and Cyber Monday as being the days to nab the best deals, Adobe predicts that for the e-commerce industry overall, the biggest discounts — an average of 26 percent off — will come on Thanksgiving Day.

More from The Washington Post:

On Black Friday, REI wants you to take a hike. Literally.

FedEx readies for a crush of holiday-season shipments

Meet BB-8, the toy that could be a breakout hit this Christmas