When Does Stronger El Nino Typically Form?

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El Nino events that have reached moderate or stronger intensity in the 1950-2019 climatology tend to form mid-year with peak intensity in December.

If early 2019 weak El Nino 2019 strengthens we’ll need to wait until July

Discussion: There are a lot of questions on whether El Nino can strengthen in 2019 and become a moderate or stronger force on global climate. Climatology tells us that of all the El Nino episodes since 1950 moderate (or stronger) El Nino episodes developed during July and peaked in strength the following December (Fig. 1). If El Nino becomes moderate or stronger in 2019 as many dynamic models indicate we’ll likely have to wait 3-4 months for onset.

Fig. 1: Based on climatology of all El Nino episodes (19) since 1950 (of which 13 reached moderate or stronger intensity) reaching moderate or stronger intensity typically occurs during July with peak in December. The 2019 forecast is uncertain although dynamic models tend to favor moderate (or stronger) intensity. A stronger El Nino to become more dominant on global climate will need to wait 3-4 months. The index used is the operational Nino index (ONI).