Moghan recommends waiting for the winds to die down so Hraesvelgr will be able to hear your call.
This quest is available if you have completed the quest The Road to Zenith.
Starting the Quest
Talk to Moghan in the Churning Mists to begin the quest.
Speak with Moghan
Go southwest to where the orange arrow is pointing in the minimap.
Defeat Threatening Monsters to the West and East of Alphinaud's Location
There are two orange arrows in the minimap. One of them points to the north. If you go there, dismount and enter the purple circle. Defeat the Melia Matron that appears. The other one is east of there. Dismount and enter the purple circle, then defeat the Melia Matron that appears there.
Speak with Estinien
Go southwest to where the orange arrow is pointing in the minimap. Talk to Estinien to complete the quest. There will be a cutscene. This one is important, so it is recommended to watch it either now or via the Unending Journey in an inn room.
Next Main Scenario Quest
After you complete the quest, talk to Moghan to accept the next quest: Heart of Ice.