Both are set to return to the Caribbean: Roach due to the death of his father, and Dowrich for personal reasons.
Roach, West Indies' senior fast bowler, claimed figures of 3 for 114 in the first Test, which New Zealand won by an innings and 134 runs. Wicketkeeper Dowrich suffered a hand injury on the first day and did not bat in either innings.
Joshua Da Silva, the 22-year-old from Trinidad & Tobago, has been added to the 14-man squad and is in line to make his international debut as Dowrich's replacement behind the stumps. Da Silva has one first-class hundred in 17 first-class appearances, but impressed when making 133* and 56* in an intra-squad warm-up match in Manchester on West Indies' tour of England earlier this year.
As well as the loss of Roach and Dowrich, West Indies have concerns over the fitness of Shimron Hetmyer and Keemo Paul. Hetmyer sustained a concussion during the T20Is series and is still being monitored, while Paul is recovering from a groin strain, and both will be assessed nearer the start of the Test.
The uncapped Chemar Holder is the most obvious like-for-like replacement for Roach, although the availability of allrounder Paul, whose most recent Test appearance came in February 2019, would strengthen the batting.
West Indies Test squad: Jason Holder (captain), Roston Chase (vice-capt), Jermaine Blackwood, Kraigg Brathwaite, Darren Bravo, Shamarh Brooks, John Campbell, Rahkeem Cornwall, Joshua Da Silva, Shannon Gabriel, Shimron Hetmyer, Chemar Holder, Alzarri Joseph, Keemo Paul
Standby: Nkrumah Bonner, Preston McSween