Moisture/water on floor near main backyard windows

Hi folks!

After some heavy rain last night, we noticed a wet spot on the floor of our newly-purchased Eichler, close to the large windows facing the backyard.

We're pretty confident it's not coming from the roof since there's no visible water/humidity above that spot, the window trim on the floor in that location also feels a bit mushy and the flooring looks a bit water-stained. It's also unlikely that this is coming from the underfloor radiant heating, since ours has been disconnected. So we're suspecting water intrusion from the outside during heavy rain.

What's the right type of professional to have come in and diagnose/quote for a repair?