By Krystina Gustafson, CNBC

Shoppers may not be as keen on Black Friday doorbusters as they once were, but one holiday shopping tradition continues to gain steam.

According to a forecast by Adobe's Digital Index, released Thursday, U.S. online sales on Cyber Monday will reach $3 billion for the first time this year, making it the largest single day for digitalsales in history.

If achieved, that figure would represent a growth rate of 12 percent year over year, and a significant jump over the course of three years. Back in 2012, sales on that day fell just shy of $2 billion.

But while Cyber Monday remains the undisputed leader for online sales, the gap is narrowing. According to Adobe's forecasts, online Black Friday sales are expected to increase 15 percent, to $2.7 billion, and Thanksgiving Day sales are seen rising 18 percent, to $1.6 billion.

"Although [Cyber Monday] isn't growing as fast, it still is the king of all shopping days online," said Tamara Gaffney, principal research analyst at Adobe Digital Index.

Overall, the Adobe Digital Index predicts online sales will reach $83 billion in November and December. While that would mark an increase of 11 percent over last year, it would also represent a slight deceleration from 2014, when Adobe said holiday sales rose by 12 percent.

Adobe bases its forecasts off data from more than 1 trillion visits to 4,500 retail sites.

Other findings from Adobe's report include the fact that 76 percent of spending this season is expected to go toward 1 percent of products, compared to the typical 65 percent. These products tend to be toys, electronics and gift cards — meaning shoppers better act fast on items in these first two categories.

"That's the dynamic that causes such a frenzy," Gaffney said.

Among the toys and electronics Adobe has pegged to be top sellers are Sphero's much-buzzed about BB-8 "Star Wars" toy, the Apple Watch and the Roku.