Juno is a champion of Carthage and Dido. Aeneas is destined to found Rome, and Venus is his mother. At about line 100 the two of them get together and conspire to get the two together. It’s really Juno’s initiative, hopefully distracting Aeneas from his real destiny. “Let us then rule this people jointly,” Juno suggests.
Create a storm while the two are out hunting. The two will take shelter, and, well, you know what happens next in a cave between two people hot for each other.
Here’s a description of the rain from Book IV, 160, that drives the lovers into the cave.
Interea magno misceri murmure caelum
incipit; insequitur commixta grandine nimbus
Meanwhile, in the sky begins the turmoil of a wild uproar; rain follows, mingled with hail.
From earlier in the chapter,
They stumbled out of Elsie’s and felt rain drops. Soon it was a deluge, with hail mixed in and lightening as the drops got larger and fell faster and closer together. They held hands as they made their way back to the hotel where they had met earlier.
The rainstorm forces the two into the cave.