Weather is significant and symbolic throughout the entire novel. When Nick first comes to East Egg to meet with Daisy, Tom, and Jordan in the first chapter, the reader is told that it is the end of spring and the beginning of the summer. THe first reason that this is symbolic is because the summer represents new life in the novel. The summer for all of the characters will bring about new experiences, some of which are not very positive. The warm weather also signifies rising tempers of the characters and flaring moods resulting in fights and arguments throughout the novel (mostly between Gatsby and Tom but also between Tom and Daisy and between Tom and Myrtle). The end of the novel brings about an end of the summer and the beginning of the fall which represents death and ending -- hence the deaths of Gatsby, Myrtle, and George and the end of Nick's "adventure" in Long Island.
Fitzgerald uses the weather as a motif in the novel to characterize the moods of the situations. Hot weather is uncomfortable and the weather becomes more and more unbearably hot as the story continues. That is because the situation between Daisy, Gatsby Tom and Nick is becoming more and more uncomfortable. This discomfort reaches its climax as the four main characters go to New York to escape the heat but ironically, the situation between the four of them becomes more and more tense. When Gatsby goes to meet Daisy, the hot weather is a clue that their situation is going to make everyone uncomfortable.