• by Sarah Mahoney  @mahoney_sarah, Yesterday

Amazon Prime Day is shaping up to be a performance monster—not just for Amazon, but for the entire ecommerce ecosystem, according to a new Adobe forecast.

Adobe expects online shopping to surge 28.4% from July 8 to 11, which translates to a $9.6 billion increase.

Some observers initially questioned Amazon’s decision to double Prime Day’s length to 96 hours, concerned the added time might dilute urgency and lead to more cart abandonment. But with recent shifts in consumer search behavior—and mounting economic uncertainty—many now expect a blockbuster. Bank of America is reportedly anticipating $21 billion in sales over just four days, marking a 60% increase from last year's sales of $13.2 billion.

Adobe forecasts that total spending on all online retail will be equivalent to two Black Fridays, as other retailers—including Target with its Circle Week—tempt shoppers with big-discount deals of their own.

Mobile continues to dominate for impulse buys, and Adobe expects it to account for 52.5% of sales—about $12.5 billion.

Less predictable is just how tempting the deals will be. Adobe forecasts that they will remain at historically high levels, providing a good value for consumers, but potentially creating profitability problems for retailers. Adobe predicts discounts will range from 10% to 24% off, inspiring shoppers to trade up to higher-end selections.

It expects the steepest cuts on apparel, estimating those discounts at 24%, compared to 20% last year,

Other average discounts: electronics at 22% (vs. 23%), televisions at 17% (vs. 16%), appliances at 16% (vs. 14%), and toys at 15% (level with last year's 15%).

Adobe also expects many shoppers to use Prime Day to jump-start back-to-school spending. A separate Deloitte survey backs that up: 53% of K–12 parents say they plan to shop the event, with 46% buying school supplies, and 40% starting holiday shopping.