Where in the world am I looking at?
You are looking at Sea Surface Temperature anomalies in degrees Celsius, or "SST anomalies" for short. Yellows and purples mean warm, greens and blues mean cold. SST anomalies are how much temperatures depart from what is normal for that time of year. This makes sense; we might say that we had a "warm winter" even though it was still much colder than summer. What we mean is that it was warmer than a normal winter; in our parlance, we would say that it was a "positive anomaly". An unusually cold winter would be a "negative anomaly". For Pacific SST, an anomaly in the range of 1.5 to 3.5 degrees Centigrade would be considered characteristic of an El Nino; the warmer and more widespread the water, the stronger the El Nino.
Last modified: November 4, 2013