Answer:
D. To express a strong feeling by making it seem insignificant.
Step-by-step explanation:
The author's most likely purpose is to express a strong feeling by making it seem insignificant. This rhetorical device is called "understatement." An understatement happens when an author describes something in a way that is less strong than what would normally be expected. In this case, although the sun is extremely strong, the speaker describes the day as "a bit warm." This device tries to draw attention to a strong feeling by making it seem insignificant.