A. Niño Regions

Niño sea surface temperature (SST) Indices are based on the average of SST anomalies across the given regions: Niño 1+2 (0-10S, 90W-80W), Niño 3 (5N-5S, 150W-90W), Niño 3.4 (5N-5S, 170W-120W) and Niño 4 (5N-5S, 160E-150W). These indices are used to monitor the conditions in the Tropical Pacific for the occurrence of El Niño or La Niña.

Warm sea surface temperatures (SSTs) across the central and eastern equatorial Pacific persisted in September with anomalies ranging from 1.0ºC - 2.5ºC. The strong warming (>2.0ºC anomaly) over the eastern equatorial Pacific was still observed and expanded westward. However, the SSTAs in the western Pacific and over most of the maritime continent were near to below average, particularly around Indonesia.

B. Indian Ocean Dipole (IOD)

The Indian Ocean Dipole mode Index (DMI) is defined as the difference between the SST anomalies (ºC) of Western (10ºS-10ºN & 50ºE-70ºE) and Eastern (10ºS-0ºN & 90ºE-110ºE) Equatorial Indian Ocean regions (WEST-EAST). The DMI values represent the intensity of the Indian Ocean Dipole (IOD); DMI values above +0.4 °C is referred as the positive IOD, DMI values below −0.4 °C is referred as the negative IOD and DMI values between +0.4 °C and -0.4 °C is referred as the neutral IOD.

Positive IOD values were still observed during the month, with the western equatorial Indian Ocean showing warmer than average SSTs while the eastern equatorial Indian Ocean was observed to be cooler than average.