During a patient retrieval from a remote mountainous area, you encounter a hiker who has been exposed to extremely low temperatures for an extended period and is now presenting with frostbite on their hands. What is the most appropriate initial step in managing this patient's frostbite?
Applying direct heat with a heating pad
Rubbing the frostbitten areas to improve circulation
Removing blisters from the affected areas
Immersing the frostbitten areas in warm water