"He feels hot in summer" should be correct too. The feminine ending in लगती refers to गरमी. उसे can be both masculine or feminine.
I think that लगती refers to the person not the weather. So this sentence could be construed as - to her in the summer, she feels hot. The first गर्मी refers to the noun "summer" as it is followed by में The second गर्मी is the adjective hot which she feels. However I am not a native speaker so feel free to correct me.
No, gender and number of lagnâ depend on what is experienced (here: garmi, a feminine noun), not the experiencer. According to the two grammars I consulted , lagnâ literally means "to be attached, applied, stuck". Thus, a literal translation of the phrase would be "Hotness is attached to her/to him in summer", i.e., "He/she feels hot in summer". If the experiencer is a noun, ko must be attached to it, e.g. admi/auret ko garmi lagti hai "The man/the woman feels hot".
richard547614..A native speaker of Urdu here: I disagree. There is no way you can tell if the sentence is about a man or a woman. उसे in the beginning is gender neutral. While summer गर्मी is feminine. Therefore लगती refers to summer.
By looking at the context. But when it's just one sentence, you can't really know, unfortunately.
Please se my answer above. उसे is gender neutral. It is the summer that is feminine.