Can I with War Caster feat cast a reaction spell on opportunity attacks triggered by the Sentinel feat?

@JeremyECrawford If you have War Caster, can you cast as a reaction on OAs triggered by the Sentinel feat?

— Daniel Gray (@filmadept) March 15, 2016

The attack granted by the third benefit of the Sentinel feat isn't an opportunity attack. #DnD https://t.co/XT5UPjjMQS

— Jeremy Crawford (@JeremyECrawford) March 21, 2016