[Text Source: NOAA/CPC and NOAA/ESRL/PSD]
Nino Regions - for data sampling of SSTs the tropical Pacific has been divided into a number of regions named Nino 1, 2,3, 4, and 3.4 (which is encompasses part of both region 3 and 4). Nino 1 is the area defined by 80W-90W and 5S-10S, Nino 2 by 80W-90W and 0S-5S, Nino 3 by 90W-150W and 5N-5S, Nino 4 by 150W-160E and 5N-5S, Nino 3.4 by 120W-170W and 5N-5S. (see: http://ggweather.com/enso/nino_regions.gif
The Climate Prediction Center has weekly data since 1990 and monthly since 1950. The Climate Diagnostics Center has monthly Nino 4 since 1948.