NOAA’s multivariate ENSO index (MEI) changed its data input from the Japanese Meteorological Agency’s JRA-55 reanalysis dataset to JRA-3Q as of January 2024. However, the data has not been attainable since May although NOAA claims the data is available (although hard to decipher with the government shutdown). MEI is a handy climate diagnostic identifying the atmospheric reaction to the SSTA/SLPA pattern across the Pacific tropics/subtropics.

The latest marine heatwave report identifies many large episodes in the northern hemisphere, common during early autumn in the current decadal pattern. Strongest marine heatwaves are off the East Asia Coast, Central Pacific, and off the Northwest Eurasia Coast. The "warm blob" in the Northeast Pacific during late summer has rapidly weakened during the past several weeks. Southern hemisphere marine heatwaves will strengthen as summertime arrives.

In a surprise, the month of September and especially October (so far) have averaged drier than expected considering the normally wet bias Australian climate produces when Indian Ocean dipole (IOD) is negative and La Nina is developing. The dry and increasingly warmer than normal pattern, especially in the East (and more recently across the North) is due to negative phase of the southern annular mode (-SAM) or negative Antarctic oscillation (-AAO) in that anomalous high pressure covers Antarctica forcing strong mid-latitude upper troughs, one of which is south of Southeast Australia.

A weak La Nina is forecast for Q4/2025 shifting to neutral phase during early 2026 and possibly to El Nino during the middle of next year. A strong ENSO episode within the next 12 months is not expected although forecast confidence in a phase change is reasonable.