Since its a screened in porch it's exposed to any snow or lot of moisture in the air so that may be what's making the wood swell up and buckle.
Mary is correct on this. Moisture in the air causes the wood to swell causing this to occur. If the undersize of the porch lacks ventilation the difference on both sides of the deck allows for cupping of the wood. If this is a three season type porch, meaning you cover the screens to keep the weather out you need to be sure you have enough ventilation below to prevent this from happening. If the underside is ventilated you may need to sand and seal the surface of the floor to prevent any rain or snow from sitting on the top after a storm.
Thank you !!!
Is this a T&G floor or more like a screwed down deck? T&G is often just set with small finish nails. at the tongue side...these do not have much holding power. When the floor is dry and flat a number of screws could be used the tighten up the whole floor. Some filler and paint and it will look like nothing is different.