hair changing with the temperature....???? (straight-wavy-almost curly)

i think its probably to do with the humidity and the heat it always causes your hair to be frizzier and do crazy things

SO
my mum has straight hair (like, 1a) and my dad has curly hair (like, type 3b i think), and i'm irish-iraqi ethnically, the most arab trait i got was my hair.
and as a kid i had curly hair (like 3a) but then it went completely straight when i was like 9. a couple of years now and it's wavy (like, 2b)
but i've noticed when it's winter and rainy my hair is straighter and when it's sunny and warm my hair goes properly wavy, almost curly. WHY IS THIS??? it's crazy cause today it's rlly wavy and big but just a couple of days ago it was basically straight! (well, a slight wave, but today there are individual waves in my hair)
HOW DOES IT CHANGE? WHY? WHICH ONE IS MY NATURAL HAIR???