The 25-year-old Jennings managed just 127 runs in eight innings during England's 3-1 series win over South Africa and was replaced by Mark Stoneman in the 13-man squad to face the Caribbeans from Thursday.
"He hasn't had the best of series. He would have known that and been disappointed," all-rounder Stokes told Sky Sports. "From the amount of runs he has got over the last two seasons playing for Durham, and getting 100 in his first England innings, he knows that he can do it."
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The left-handed Jennings scored 112 on his Test debut in India last December and followed it up with a half-century in the next Test against the world's top-ranked side. But he has failed to show the same level of consistency since, with 48 his highest score in the four-Test home series against South Africa.
Jennings will return to Durham and look to recapture the form that earned him selection. Surrey batsman Stoneman is set to make his debut at Edgbaston and the 30-year-old will become former captain Alastair Cook's 12th opening partner since the retirement of Andrew Strauss in 2012.
England also called up 20-year-old Hampshire leg-spinner Mason Crane for the first time in the longest format after he made his T20I debut in June.
Skipper Joe Root said new leg spinner Mason Crane was typical of the modern cricketer who feels at ease in switching between the many formats of the game.
"He is a very exciting prospect and this is a great opportunity," said Root. "T20 is part and parcel of the schedule and you've got to be able to switch between formats. He'll have a good week's preparation now."
The highly rated leg-spinner played two T20 games for England against South Africa earlier this summer, effectively sealing the series by having AB de Villiers caught in the deep off his googly delivery.
He is not certain to play at Edgbaston, where the timing and pink ball is likely to favour the seamers, and his first-class record is modest — 70 first-class wickets at almost 42 runs each. But his inclusion in the squad over his Hampshire team mate, off-spinner Liam Dawson, probably reflects England's desire to take a leg-spinner to Australia for the forthcoming Ashes series.
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