This study used the Empirical Orthogonal Function (EOF) analysis which is a technique of descriptive multivariate statistics. It is a useful technique in the meteorology and oceanography. The original purpose of EOF was to reduce the large number of variables of the original data to a few variables, but without compromising much of the explained variance. Lately, however, EOF analysis has been used to extract individual modes of variability such as rainfall data, (A. Hannachi, 2004) known as teleconnections.
For technical applications EOF to study the variability of rainfall will reduce the amount of data to only the dominant mode and can explain the changes of precipitation in a clear overview. The algebraic essentials of EOF analysis can be described as follows. In the EOF technique, the data was collected as a grid of the study area. The data are first arranged into matrix where is the rainfall amount collected at the time and station . Which are arranged data as shown Figure 2.1.