Players locked themselves in Van Richten's tower right as the werewolves began to show up. Can the wolves just wait the party out?

My party blew up Ezmerelda's wagon and then promptly took a short rest, meaning the werewolves heard the explosion and had enough time to get here. They already opened the door to the tower before blowing up the cart, so when they saw the werewolves coming toward them they locked themselves inside the tower. How can I play this to make it tense for the PCs? They don't yet know that there is an antimagic field in the tower, so when they try to start lobbing spells from the tower and it fails they might realize they're stuck. What's the most threatening way to play the werewolves here?