How can we reconcile the fact that solar and lunar eclipses are signs of God's warning and wrath, necessitating a rush to prayer, remembrance (dhikr), and supplication (du'a), with our prior knowledge of them long in advance? And would the Prophet's ﷺ fear have been of the same intensity if he had known about them beforehand?

Eclipses (solar and lunar) are two signs among the signs of Allah, with which He frightens His servants. The believer does not know what punishment or wrath might accompany them. This is why the Prophet, peace and blessings be upon him, would be alarmed upon seeing clouds or wind, because anticipating the occurrence of a sign does not eliminate fear. Just as a person anticipates rain, he does not know what benefit or harm might accompany it. This is contrary to the state of the heedless, who await rain only to be met with punishment. The Prophet's alarm was due to his knowledge of his Lord and his intense fear of Him.