You've basically got a double redirection.
nmap -sT localhost > hist
should do it. Unless the pipe to cat is doing something I'm missing, which is very likely.
Is that making the difference between on-the-fly reporting and a finished report? Is that what you were specifically interested in? I would think that would just drag it off to cat and spit out the file.
Anyway - depending on your specific goals, you might also want to look into 'tee'.