Amazon Prime Day, the four-day period during which the e-commerce company offers special deals and signs up new Prime members, helped lift total online sales across America by 30.3% for the period to $24.

Online spending is expected to surge to $23.8 billion across U.S. retailers during a 96-hour Amazon Prime Day event this week, according to an Adobe Analytics forecast released on Monday, as shoppers seek strong discounts on back-to-school gear ranging from apparel to electronics.

Momentum Commerce, which manages online sales for 50 brands, said its Amazon purchases plunged 41% on Tuesday when compared with the start of Prime Day last year.