I've already made my case for why Apple (NASDAQ:AAPL) might end up missing its revenue guidance for the fiscal fourth quarter, which closes on Sept. 30. My thesis is that Apple's strong Q4 guidance was issued before one of Apple's key suppliers for vertical-cavity surface-emitting laser (VCSEL) arrays, Finisar, ran into manufacturing delays related to a process change. I could certainly be wrong, but the timeline of events supports my theory.

Apple investors now have another data point that could suggest a Q4 miss is on the horizon.

iPhone X being splashed with water

Everyone wants iPhone X, which won't ship until fiscal Q1. Image source: Apple.

iPhone 8 demand is modest

KGI Securities analyst Ming-Chi Kuo released a research note yesterday (via 9to5Mac) suggesting that iPhone 8 demand is proving to be tepid, as most customers are much more interested in the iPhone X, which won't launch until November. Apple is still quoting shipping times of one to two weeks for iPhone 8 pre-orders, whereas prior years often saw shipping times quickly slip to three to six weeks at this stage following the unveiling. As of yesterday, some configurations were still available for launch day (this Friday).

Those shipping estimates don't inspire a lot of confidence in demand for the iPhone 8 and 8 Plus, which may be instrumental in hitting the ambitious forecast of $49 billion to $52 billion in sales. There is some pricing upside since Apple bumped up starting prices to $699 and $799 for iPhone 8 and 8 Plus, respectively, but the Mac maker would still need considerable unit demand to hit its outlook. That guidance was provided only about a third of the way through the quarter on Aug. 1.

Silver linings

It's not all bad news, though. Kuo also believes that demand for the new Apple Watch Series 3 with cellular is enjoying "significantly stronger-than-expected pre-order demand," also pointing to preliminary shipping estimates of three to four weeks. The analyst had previously expected cellular models to comprise 30% to 40% of volume, but now believes that cellular models could end up being 80% to 90% of volume.

On the base aluminum Apple Watch Series 3 models, cellular connectivity is a $70 option, while the higher-end stainless steel and ceramic models all include LTE -- and also received price bumps. This all bodes well for Apple Watch average selling prices (though Apple likely won't disclose financials).

Perhaps more importantly, all of the customers that are awaiting the iPhone X are doing just that: waiting. They're not switching to Android. Those sales are just being shifted from fiscal Q4 to fiscal Q1. On the August earnings call, CEO Tim Cook discussed purchasing delays caused by persistent iPhone rumors: "We do think that based on the amount of rumors and the volume of them, that there's some pause in our current numbers. And so where that affects us in the short term, even though we had great results, it probably bodes well later on."

In this case, "later on" means in the coming months following the November launch of iPhone X as Apple scrambles to achieve supply/demand balance.

Evan Niu, CFA owns shares of Apple. The Motley Fool owns shares of and recommends Apple. The Motley Fool has a disclosure policy.