This is a fairly straightforward rain water leak; leaky door membranes are not unique to Nissans, they are one of the most common leaks on any kind of car.
Solution: Replace the door membrane and seal it properly, and recommend that we do all four doors because if one has perished, the others are likely not far behind. As it's not an expensive fix in terms of parts, it makes sense to do it.
The car will also need to be dried, so the front seat will come out, the carpet lifted up, the water underneath extracted, and then we will put our drying machines on it.
We have been repairing leaks and drying cars for over 30 years
Up to a third of the cost of your car was computers, processors and sensors. Delicate electrical systems hidden under your carpets, which might now be sitting in water.
Car Leak Repair
Question: "If I use a car cover and get the car dried out, can I bring it to you in the summer?"
Answer: You could do, but we strongly advise against this.
The car will be very unlikely to dry on its own. You really need to get those carpets lifted, suck out the water and dry the car with blowers and dehumidifiers. Otherwise, the car will remain wet.
You are probably already experiencing condensation and a damp smell. Putting a car cover over it will just increase the condensation and warmth while making the car nice and dark. You will be creating a mould farm.
So stay away from car covers, but by all means, keep the car garaged and make serious attempts to dry the car if you can.