Watermelon - picking and managing them during heat
There may be different varieties of watermelon that behave differently, so I can't guarantee that this will work for you.

The way I've always done it is to only cut up what I'm going to eat.

We cut across the watermelon in the shorter direction, starting at one end, producing circles about 1-1.5 inch (2-3 cm) thick.

Here's an image of what removing the first slice looks like:



You can cut these circles into wedges or remove the rind and cut into pieces.



This leaves the remainder of the watermelon intact with only a single side open to the air, and that end is covered in plastic wrap (cling film) and stored in the refrigerator.