The entry for
Jenna notes the popularity of the name was influenced the character "
Jenna Wade" on the show
Dallas.
According to Wikipedia,
"The character of Jenna Wade was originally portrayed by Morgan Fairchild for one episode in 1978; Jenna was then portrayed by Francine Tacker for two episodes in 1980. When the character was brought back in 1983, the part was recast for the second time, this time with Jenna being portrayed by Priscilla Beaulieu Presley."
I would guess the rise in popularity of the name coincided with the (re)introduction of the character
Jenna, being played by a famous actress, and thus the name gained more visibility.