fifos are not for saving or reading more than once. You may find tee better suited to your goals.
Untested guess at what you want(split a network stream):
mkfifo myfifo1 myfifo2 && curl -s http://192.168.1.27:8554 | tee myfifo1 > myfifo2;
Other guess at what you want(display and save on rpi):
raspistill --fullpreview --output - >> jpgs.dat
or using more than one file in a loop
raspistill --fullpreview --output $(date +%Y%M%dT%H%m%S).jpg
or using raspivid
raspivid -fps 2 --timeout 0 --fullscreen --output $(date +%Y%M%dT%H%m%S).h264
Note that you can set the fps on raspivid and with it's temporal compression it may be better than looping raspistill in some conditions.