Q: iPhone 6 switched off suddenly hot and humid weather

Hey bbayatm,

Thanks for the question. If I understand correctly, the iPhone turned off and is not turning back on. I would recommend that you read these articles, they may be helpful in troubleshooting your issue.

If your iPhone, iPad, or iPod touch doesn't respond or doesn't turn on - Apple Support

If the iPhone was getting too hot, this article explains what the iPhone will do. 

Keeping iPhone, iPad, and iPod touch within acceptable operating temperatures - Apple Support

If you were concerned about possible water damage, this article shows where the indicators are. 

Liquid damage to iPhone or iPod isn't covered by warranty - Apple Support

Thanks for using Apple Support Communities.
Have a good one