This was not a planned trip as of this morning, so it sounds like his brother’s condition may have taken a bad turn.
According to Fox News:
President Trump is expected to travel to New York on Friday to visit his brother Robert Trump, who is said to be very ill, in the hospital.
A senior administration official said Friday that the president “has a very good relationship with his brother and his brother is very special to him.”
The president will is expected to travel on Marine One to New York City Friday afternoon.
The president’s brother was reportedly hospitalized in the intensive care unit at Mount Sinai Hospital in New York for more than a week earlier this summer.