The winners will face Sussex Sharks in the semi-finals, which take place on Finals Day at Edgbaston on Saturday September 15.
Play will start at Taunton at 1pm tomorrow, weather permitting. The forecast is a lot better.
Umpires Neil Mallender and Steve O’Shaughnessy ruled that the reserve day would have to be used after a 4pm pitch inspection, an hour after the scheduled start.
Rain had fallen heavily throughout the morning, creating patches of casual water on the outfield as well as saturating the covers.
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A sell-out 7,500 crowd had been expected, but many supporters did not bother to turn up at the Cooper Associates County Ground because the weather was so bad.
Somerset will not be refunding ticket money to those unable to attend if play is possible tomorrow.
A club statement read in part: “Should the match have to take place on the reserve day then we are afraid that we would not be in a position to refund match tickets because the match will have taken place.
“It would also be extremely difficult from a logistical point of view to refund the tickets and re-sell them in such a short space of time.
“We understand that the match being played on the reserve day may make attending the fixture rather more difficult for some people and this is unfortunate for all concerned.
“However, cricket supporters are well aware of the major match protocol and the need for a reserve day within that procedure.
“Those who are unable to attend may wish to utilise our social media channels to facilitate the transferal of match tickets at face value.
“However, Somerset County Cricket Club can in no way condone any profit making or ticket touting in regard to this or any fixture.”
The other semi-finals at Edgbaston will see Lancashire Lightning take on Worcestershire Rapids. The draw was made shortly after play was abandoned at Taunton.