Apple

Apple could sell 36 million of its smartwatches over the first 12 months they're on the market, according to the latest prediction out of Wall Street. And that's a conservative estimate.

The new figure comes from Morgan Stanley analyst Katy Huberty, who is raising her Apple Watch sales forecast by 20 percent from the earlier figure of 30 million.

It might have been even higher if Apple were having better luck with its supply chain for the smartwatch, its first foray into wearables.

The market for smartwatches is a bustling one, with a wide array of options including the Samsung Gear S and Android-based models including the LG G Watch R and the Motorola Moto 360 . But while smartwatches from those and other companies have been on the market for months, none has yet lit up interest among consumers in the way that Apple's entry is expected to. In 2014, all smartwatch vendors combined shipped only 4.6 million devices, according to Strategy Analytics.

The Apple Watch is available in three different flavors -- the entry-level Sport version, the midlevel Apple Watch and the luxury Apple Watch Edition. The Sport version starts at $349, the Apple Watch at $549 and the Apple Watch Edition at $10,000. For the moment, they're available for purchase through Apple only by reservation at an Apple Store or via online sales, and can also be found in a sprinkling of luxury stores.

The devices were back-ordered as soon as they went on sale in April, with delivery dates stretching into June and July. Apple hasn't revealed any numbers for initial sales (in contrast with its typical approach when a new iPhone goes on sale), and it's unclear how much of the delay stems from strength of consumer demand and how much from supply shortages or manufacturing issues.

Apple CEO Tim Cook last month spoke in only the most general of terms about the start of Apple Watch sales.

"Right now demand is greater than supply so we are working hard to remedy that," he said. "I'm generally happy how we're moving on with the ramp."

Demand outstripping supply is a familiar story for Apple whenever the company rolls out a new product. But in the case of the Apple Watch, the limited supply could end up costing the company a healthy number of sales, according to Huberty.

Her figure of 36 million in unit sales is based on polling. It takes into account only those polled who said they would "definitely" buy the Apple Watch and not those who said they would "probably" buy it. It also assumes that 50 percent of buyers will be in the US.

Huberty has been tracking US consumers' interest in the Apple Watch since it was first announced last September and said that surveys showed prospective demand rising consistently over the past six months, and has spiked in recent weeks.

"US Apple Watch demand increased around 60 percent since March," she said. "Importantly, Apple enjoyed the biggest increase in Watch purchase intentions post making the product available in mid-April. While the survey data extrapolates to 50 million annual Watch demand, we see this as a bull case given supply limitations."

In other words, Apple would be on track to sell 50 million of its smartwatches in the first year if only it could make that many.

Huberty said she believes supply will "significantly undershoot demand" over the first six months. But as the production process ramps up and more orders are filled, supply should start to catch up with demand. As a result, the analyst is sticking with her current Apple Watch sales forecast for the June and September quarters but has increased her estimates for the December and March quarters by 6 million units.

That mostly upbeat forecast is contrary to the more bearish scenario envisioned by investment firm KGI Securities, where Apple analyst Ming-Chi Kuo has often been on the mark with his predictions. KGI has slashed its annual shipment forecast for the Apple Watch in half, 9to5Mac said Wednesday. Based on slower demand for the watch, KGI said it now believes Apple will ship only 15 million watches this year, down from the prior estimate of 20 million to 30 million units.

Now playing: Watch this: Apple Watch: Extremely ambitious, far from perfect

In March, before the watch went on sale, Fortune polled a series of analysts for their estimates and got numbers ranging from 8 million to 41 million, with an average of 22.5 million in annual sales. In early May, UBS analyst Steve Milunovich lowered his estimate for Apple Watch sales to 31 million from 40 million for Apple's fiscal 2016, which starts in October. However, the analyst said he was more bullish on the watch over the longer term, according to Barron's.

In her investors note, Huberty also chimed in with iPhone sales predictions.

Demand for the iPhone continues to surpass expectations even though the iPhone 6 is nearing the end of its product cycle, meaning the next iPhone is only about four months away from its release. Based on results from Morgan Stanley's AlphaWise Smartphone Tracker, which uses Web searches to compile sales data, the analyst has raised her iPhone sales forecast for the current June quarter to 50 million from 46 million. During the same quarter in 2014, iPhone sales reached just 35.2 million units.