As slow moving as Harvey likely will be Storm Surge will still occur, and probably be prolonged and pile up. Especially if it stalls near or just at the coastline. If anything it could be higher in areas than they are predicting. If it were ramping up quickly AND moving quickly then it would be less, but ramping up and crawling is a near worst case.

12Z GFS: (Pressures initialized too high)
landfall Saturday morning, Cat 3. stalls just inland until Wednesday! and then moves northeast inland.

12Z Euro Landfall Saturday morning Cat 2 (obviously not strong enough based on new pressures) Exits out into the Gulf Monday, then second landfall in western LA on Wednesday, cat 3. Rain and huge coastal impacts all along E. Texas and Louisiana.

12Z HWRF Landfall early saturday morning as a cat 3. stalls just inland.

3k nam has pressure down to 873 (record Cat 5) before landfall, but is not a tropical model.