On Thursday, tech giant Apple (NASDAQ:AAPL) sent out invites to its annual September product event. The event will take place on Tuesday, Sept. 10 at 10:00 a.m. PDT. iPhones are typically the main product that Apple announces at its September events -- and this year looks like it will be no exception. The company has three new iPhones in its pipeline to show off.

Investors will be watching the event closely, as the tech company's fall lineup of new products wasn't enough to grow sales during the holiday season last year. Apple missed the midpoint of its revenue guidance range for its first quarter of fiscal 2019 (a period that lined up with the fourth quarter of calendar 2018) by a whopping $7 billion.

Ahead of the event, here's a preview of what to expect.

Apple CEO Tim Cook kicks off Apple’s March 2019 event.

Apple CEO Tim Cook. Image source: Apple.

New iPhones

The tech giant is readying two new versions of its iPhone XS and iPhone XS Max. They'll be differentiated with "Pro" branding, according to Bloomberg's Mark Gurman. Giving credence to this rumor, the Bloomberg journalist is known for his reliable sources from within Apple -- and he has a great track record with predictions for the tech company's product features. Gurman's sources also say Apple will unveil a predecessor to the iPhone XR.

As was the case with the previous iPhone lineup, the new "Pro" versions of the iPhone XS and XS Max are expected to have OLED displays, respectively measuring 5.8-inches and 6.5-inches diagonally. They'll sport major camera upgrades, a new matte finish, improved Face ID, and faster performance thanks to a new processor, Gurman predicts. The iPhone XR is also expected to boast a new camera and processor.

In the first full quarter of iPhone sales following last year's iPhone launch, iPhone sales tumbled 15% compared to the same period in the prior year. Accounting for 62% of the holiday quarter's total sales, the segment's poor performance unsurprisingly weighed on the tech giant's overall performance. Total sales declined 5% and earnings per share fell 7.5% during the period.

Investors will be hoping these new iPhones can create enough excitement going into its first quarter of fiscal 2020 -- which coincides with the fourth calendar quarter of 2019 -- that Apple will be able to grow its overall sales this time around.

Services

Looking beyond iPhone, another key topic to surface during the event may be Apple's services. The company has recently been doubling down on its services business as it attempts to find more ways to monetize its active installed base of users across its iOS ecosystem. In addition, the company likely hopes to become less dependent on the iPhone.

This spring, Apple announced four new services, including Apple TV+, Apple News+, Apple Arcade, and Apple Card. While Apple News+ and Apple Card have already been launched, the company has yet to release the other two services. Expected to launch them sometime in the fall, Apple may share more details on the services, including pricing.

The tech company is also reportedly readying new MacBook Pros, an updated Apple Watch, new iPads, and the Mac Pro it unveiled (but has yet to launch) in June. But it's unclear whether any of these products will be shown off during the event, as Apple typically holds a second event in the fall where it unveils more products. Some of these products, therefore, may be slated for an event later this year.