In a match that guaranteed qualification for the winner, the West Indies were bowled out for 198 to give Scotland a gilt-edged chance of participating at their fourth finals when the World Cup is hosted in England next year.
Scotland were 125 for five in their chase with some 14 overs still in hand when rain began to fall in Harare with a light shower unexpectedly turning into a heavy thunderstorm.
The contest was called off around 30 minutes after the players had left the field, allowing the West Indies to avoid a major upset.
Scotland opener Safyaan Sharif removed Chris Gayle with the first ball of the game and, along with Brad Wheal, went on to take three wickets as all the bowlers impressed.
Evin Lewis, who scored 66, and Marlon Samuels who scored 51 were the only batsmen who made significant contributions for the Windies.
Scotland lost their captain Kyle Coetzer in the third over as they began their chase and were constantly under pressure but looking to break the shackles when the storm arrived.
George Munsey was 32 not out in a holding role while Michael Leask was on the front foot and had scored 14 runs off 10 balls.
On Thursday, hosts Zimbabwe can make sure of the other qualifying berth if they beat the United Arab Emirates in their last qualifier in Harare, although the venue was left heavily waterlogged by Wednesday’s rainfall.