The Australian Bureau of Meteorology (BoM) has reported that three out of four criteria for the development of the El Nino weather phenomenon have been met.
However, the Pacific Ocean and atmosphere have not fully coupled, which is a characteristic of El Nino events. Nonetheless, sea surface temperatures (SSTs) in the central and eastern Pacific are exceeding the El Nino threshold, and models indicate that further warming is likely to persist until at least the end of the year.
The current El Nino Southern Oscillation (ENSO) outlook remains at El Nino alert status. Past data suggests that when the El Nino alert criteria have been met, an El Nino event has typically occurred about 70 percent of the time.
El Nino is caused by the warming of SSTs in the Pacific Ocean and is associated with drought and deficient rainfall in regions like Asia, particularly India.
The Southern Oscillation Index (SOI) has shifted back to neutral levels in the past month, with the 30-day SOI at +3.9 for the 30 days ending July 16, and the 90-day SOI outside El Nino thresholds at -5.2.
The BoM upgraded its El Nino watch to an El Nino alert on July 6, indicating a 70 percent chance of the weather event occurring. However, sustained changes in wind, cloud, and pressure patterns towards El Nino-like conditions have not been observed, which explains why the Pacific Ocean and atmosphere are not yet fully coupled.
On another note, the Indian Ocean Dipole (IOD) is currently neutral, but models suggest a positive IOD is likely to develop in late winter or early spring. A positive IOD can further decrease rainfall and aggravate the El Nino situation.
While the models show it is highly likely that tropical Pacific Ocean temperatures will reach El Nino levels during winter, the atmosphere has not fully aligned with El Nino conditions yet, though meeting the alert criteria.
