Have you verified the instances/microflow where the REST call is made happens only once?
Could it be that the list contains two objects? Because it seems that strangely enough the REST service responds with a list of Weather instead of just one object.
Regards,
Ronald
[EDIT]
It seems that you also pass the object along. Is this a submicroflow? Or is it used in a form. Do a find usage of this microflow and try to figure out what could be the reason that the microflow is triggered twice. You could also try to disallow concurrent usage of this microflow ( https://docs.mendix.com/refguide/microflow#3-3-error-microflow).