Modern Tempest was able to hold temporally with his magic the god Drogue, whose power, according to Donna Troy eclipsed those of Superman.
Garth also survived re-entering the atmosphere and falling into the ocean.
Garth fought and was about to defeat Donna Troy.
Tempest defeated three Atlantean sorceress with his magic.
Garth can use the Eldritch blast, that can reduce to ashes a normal human, damage Donna Troy and pierce a demon's chest.
Dick Grayson says that Tempest moves very fast for him.
He can take bullets.
Tempest can damage the skin of demons with his water blasts.
I don't know much about classic Tempest. Maybe
@Endless Mike can help with that.
Meanwhile, Storm can boil water:
Defeated Super-crocodiles:
She can also control ocean currents:
And can control the air on people's lungs and freeze the heart and veins of other people:
I guess Storm wins this. She can freeze Tempest's veins or attacking him with a lightning when he is swimming on the ocean.