Sea Surface Temperature Anomalies (SSTA) of the 1998 El Ni簽o. The SSTA are derived from the Advanced Very High Resolution Radiometer (AVHRR) Optimally Interpolated SST that are provided by the Group for High Resolution Sea Surface Temperature (GHRSST) and also use NOAA's National Centers for Environmental Information (NCEI) climatology. The AVHRR instruments have been flying onboard NOAA's operational polar orbiting satellites since 1981 beginning with NOAA-7 and continuing to present with NOAA-19.