Bring 4 quarts water to boil in large pot. Add 1 tablespoon salt and macaroni and cook until nearly tender, about 5 minutes. Drain in colander and rinse with cold water until cool, then drain briefly so that macaroni remains moist. Transfer to large bowl.

Stir in onion, celery, parsley, lemon juice, mustard, garlic powder, and cayenne, and let sit until flavors are absorbed, about 2 minutes. Add mayonnaise and let sit until salad texture is no longer watery, 5 to 10 minutes. Season with salt and pepper to taste. Serve. (The salad can be covered and refrigerated for up to 2 days. Check consistency and seasonings before serving.)