(AMZN -2.56%) set sales records in the fourth quarter of 2019, reporting a 21% year-over-year jump in revenue. Total revenue during the period was about $87.4 billion, beating analysts' average forecast for $86.0 billion.

With such a strong fourth quarter last year, you'd think it'd be hard for the e-commerce giant to beat this record performance in the fourth quarter of 2020. But a closer look at Amazon's recent performance and one key detail about this year's fourth quarter suggest the online shopping specialist will once again deliver record fourth-quarter results.

Investors should expect a huge fourth quarter from Amazon -- here's why.

A couple shopping online together.

Image source: Getty Images.

Prime Day comes to Q4

Unlike in fourth quarters past, Amazon's fourth quarter of 2020 will benefit from the inclusion of Prime Day. The member-only shopping event typically took place during the summer. But because this summer was plagued with coronavirus-related business challenges, Amazon's network of sellers wouldn't have been able to fully capitalize on Amazon's Prime Day event.

Of course, Amazon isn't one to miss out on an opportunity. So instead of canceling Prime Day 2020, the company simply shifted it to October. Prime Day will occur on Oct. 13 and Oct. 14 this year, lasting for 48 hours straight. The massive Prime member event will run in 19 countries. 

Amazon's event will include typical major sales of its own devices as well as greater efforts to support small businesses during a challenging year. Amazon is giving out $10 credits to members who spend $10 on select items from small businesses.

Some notable deals during Prime Day will be 60% of third-generation Echo Dot's, 33% off DJI Mavic Mini Drones and Osmo cameras, 36% off Nintendo Switch Online Family Memberships, and more.

Prime Day isn't your average shopping event. It typically yields sales that surpass Amazon's Black Friday and Cyber Monday sales from the prior year. 

Strong momentum

Even without a fourth-quarter Prime Day, Amazon's recent sales momentum suggests the e-commerce giant was likely due for a record fourth quarter. The company's sales soared 40% year over year in Q2 as consumers all around the world turned to e-commerce as an ideal shopping solution while sheltering from home. Revenue for the period was $88.9 billion, crushing analysts' average estimate for $81.5 billion.

The circumstances surrounding COVID-19 arguably accelerated adoption of e-commerce -- both by businesses who are building out their online stores and consumers. This trend will likely persist, albeit likely at a slower pace, in Q4.

Analysts certainly seem to agree that Q4 will be big for Amazon. On average, analysts are estimating that Amazon's fourth-quarter revenue will jump 27.3% year over year. This would be an acceleration from the growth Amazon saw in the fourth quarter of 2019.

Notably, however, Amazon still has to report its third-quarter results. When the e-commerce giant reports its third-quarter results later this month, investors can look to management's guidance for Q4 to see if investors and analysts' hunch that Q4 will be big is on the right page.