Troubleshooting the above warning message in Nagios:

i) If you can specify the IP address of the host with its port number try specifying it that way instead of the host name

ii) Check the the time that is set for the http check parameter and based on it try setting the -w (warning message) parameter (sample setting: command_line /usr/lib/nagios/plugins/check_http -H mywebsite.com -t 60 -w 55)