Though this TAF is from Fortaleza international airport located in northeast Brazil...where it really gets pretty damn hot sometimes....the RMK PDH is not related to any indication of temperature or any other weather condition. Once a asked this same question to an ATC controller here in Brazil and I was told that in this case it stands for the initials of the person/officer responsible for writing the MET message and has no operational purpose. Seemed like a reasonable explanation to me.
Cheers!