Is it normal for a roof to leak in heavy rain?
No. A roof in good condition keeps out a downpour as well as a drizzle.
When water only appears in the worst storms, one part of the roof is coping with ordinary rain but not with a lot of water arriving fast or sideways. Wind pushes rain under laps and behind metal, which is why these leaks so often lead back to flashing at a chimney, a skylight or a wall.
Other usual suspects: a valley or gutter that spills over when the volume spikes, an aging seam on a flat roof, a gap around a vent boot.
Near open water, as in Parole between the Severn and South rivers, storms push rain sideways under ridge caps and rake edges too, so those get checked along with the flashing.
Keep a short log: the date, which way the wind blew if you know it, and exactly where the water appeared. It saves time finding the way in on the roof.
Do not wait for the next big storm to prove it. A leak that only shows in downpours is still wetting the deck and insulation each time, just in smaller amounts.
Next time it pours, note where the water shows, then book a visit. A leak like this is booked within 48 hours.