Nagios - can it do what I want?

What I’d like is for it to “look” at my cacti graphs and based on a historical value, send an email if it goes above or below a certain threshold.

For instance, it will look at a traffic graph. It is Tuesday today, so I want it to look at the value for this time last week and if it deviates significantly, send a warning.

However, it would need to be smart enough to not send a warning if last weeks spike was an anomaly and this weeks data is normal.

Can it do this?

sure, if you write the plugin which reads the graphs…

nagios makes immediate checks basing on plugins… cacti has a threshold plugin which MAYBE does what you are looking for…
I think there’s a fault in how you want to monitor your graphs… having a check of that type would give you an alert for a full week because of a network spike on any day… i don’t think you want an alert ll the time even if 99% of the time the parameter you are looking at is ok.