Thread Subject: EOF/PCA with SST

Hello everyone,
I would like to do a EOF/PCA analysis on SST to identify different types of El Nino modes.
I know that there is a function in matlab I can use: princomp, I also read that I could use pcacov if I used it directly on a covariance matrix.

My main problem is, however, that I don't know how to format my input data :-(

So far I have a global grid 180x360 (lat x long) of SST for 360 months. (180 x 360x 360)
I would only extract the tropical Pacific SST and I also know that I have to subtract the climatological seasonal cylce before I apply PCA but that will still leave me with a 3D data set.
What am I forgetting? How do I change the input format? Do I have to calculate averages over time?

I'm lost here and any help would be greatly appreciated
All the best
Sandra