Ireland, choosing to bat, were restricted to 183 for eight from their rain-reduced allocation of 48 overs, and the target was increased under the Duckworth-Lewis Method which is used to recalculate totals in weather-affected matches.
Jeremy Bray hit the top score for Ireland of 41 from 72 balls, and Andre Botha gathered 28.
Chris Gayle, Daren Powell, and Dwayne Bravo collected two wickets apiece for West Indies.
West Indies had early success, when William Porterfield was caught at first slip off Daren Powell for a duck in the second over touching a short, rising ball.
Eoin Morgan came and took the sting out of the West Indies attack with a stand of 58 for the second wicket with Bray.
Bray was given a reprieve on 34, when he drove Daren Powell straight into the lap of cover fielder Marlon Samuels, who failed to hold onto a sharp chance in the 14th over.
West Indies did not have to wait too long for more success though.
Morgan was caught at deep fine leg off Powell for 18, when he got carried away, hooked at a short, lifting delivery and his top edge flew almost 50 yards behind the stumps and keeper Denesh Ramdin held a superb running catch.
Two wickets in the space of nine balls further slowed Ireland's progress in the middle of their innings, and left the visitors on 82 for four.
Niall O'Brien was caught behind off Ian Bradshaw for 11 in the 21st over nibbling at a ball moving away, and next over, Bray drove at a slower ball from Jerome Taylor and was caught at mid-off for 41.
Kevin O'Brien arrived to consolidate for Ireland in a partnership of 47 for the fifth wicket with Andre Botha before he swung at a delivery from Gayle and was caught at deep mid wicket for 16 in the 36th over.
Gayle struck again in the 40th over, when Botha sliced a pull, and he was caught at backward point for 28.
But the weather interrupted and the players spent 70 minutes off the field, before they returned, and Bravo collected the wickets of Andrew White, bowled for 18, and John Mooney, caught behind, for a duck.
Ramdin ended with four catches.
Both sides made one change to their line-ups from their previous matches.
Ireland brought John Mooney in to replace captain Trent Johnston, who has not recovered from a shoulder injury he sustained in last Saturday's stunning win against Pakistan.
Kyle McCallan led the Irish side in Johnston's absence.
West Indies included Ian Bradshaw ahead of Corey Collymore in a rotation of their bowlers.
Both sides have already secured their places in the Super Eights, but the outcome of the match will be vital, since the winning side will start the next stage of the competition with the two points they will gain from victory.
West Indies lead the group with four points, Ireland are second on three, Pakistan are third on two points, and Zimbabwe are last on one.
Ireland 183 for 8 in 48 overs (Jermey Bray 41, Andre Botha 28, Kyle McCallan 20 n o; Gayle 2 for 23, Powell 2 for 24, Bravo 2 for 35) Vs West Indies (yet to bat)