2017 MacBook Pro temperature rising when connected LG 27UD88

Hi,

I've bought 2017 MacBook Pro 13" without touchbar and it's working really well but I've got one problem with it.

When I connect USB-C external LG 27UD88 monitor via usb-c cable (1440p scaled) temperature immediately raise up about 20 degree. From ~50 celsius to ~70 celsius.

Nothing more happens. Only safari open with 1 tab. Just after about 1min it's 20 degree up. Is this normal behavior? It's a little disturbing because fan start to be heard and noise isn't enjoyable. Especially it's very annoying when I'm working with more tools open, then fan continuously is at 7200RPM.