The descriptions mention powering up in cold and hot climates respectively. What does that mean, exactly?
Polar Hunter increases your attack by 15 while fighting in a "cold" area (one that lights your stamina bar blue)
Tropic Hunter increases your attack by 15 while fighting in a "hot" area (one that lights your HP bar red and drains it)
Both of these negate the negative effects of the given area as well. They also give further bonuses for drinking a cold drink(polar hunter) or hot drink(tropic hunter).
North/South Wind Hunter were the translated names from the japanese version, pre-localization.
Testing Polar Hunter I got: Starting Values: 211 Def, 130 Att (Mizutsune Longsword) No Food, No att/def increasing armor skills
Upon Entering Cold area: 231 Def (+ 20 Def) and 145 Att (+15 Att)
After Drinking a Hot Drink (( +Negate Cold status)) : 231 Def, 145 Att
After Drinking a Cold Drink, not in a Cold area: 211 Def, 135 Att (+ 5 Att)
After Drinking Cold Drink and in cold area:231 Def, 150 Att (+20 Att)
So you get +5 Att from a cold drink, and +15 att/+20 Def by being in a cold area, and you can stack these buffs for a total of +20 att/+20 def. Tropic Hunter should work the same, just change out "Cold" with "Hot"