Warmest season vs. hottest season

[Hotty]

English Grammar Tests, Elementary Level

ESL/EFL Test #119 "Weather Test (6)", question 4

In North America, the warmest season of the year is usually the ..........

(a) spring
(b) summer
(c) fall

English Grammar Tests, Elementary Level

ESL/EFL Test #119 "Weather Test (6)", answer 4

In North America, the warmest season of the year is usually the summer.

Correct answer: (b) summer
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warmest or hottest

[Gray]

Google "hottest season" and read why 'hottest' isn't appropriate here. But, I still have doubts as dictionary doesn't speak against the use of 'hottest' here.

Natives, please help.
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First lesson - English, not english. I, not i. ~A student of English