How can I tell when a whole melon is ripe enough to eat?

If the melon is ripe, it will yield noticeably to the pressure of your finger. A cantaloupe's stem should be gone, leaving a smooth symmetrical, shallow base called a "full slip.” If all or part of the stem base remains, or if the stem scar is jagged or torn, the melon is probably not fully matured. Second, the netting, or veining, should be thick, coarse, and corky, and should stand out in bold relief over some part of the surface. Third, the skin color between the netting should have changed from green to yellowish gray or pale yellow.
 
A ripe honeydew's surface has a soft, velvety texture. A slight softening at the blossom end, a faint pleasant fruit aroma, and yellow-white to creamy-white rind color also indicate ripeness.
 
A ripe watermelon's surface should be relatively smooth. The rind should have a slight dullness, meaning it shouldn't be too shiny or dull. The ends should be filled out and rounded, and the underside should have a creamy color.
 
Source(s):
Wholefoodsmarket.com