Fuel For La Nina In Question

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Upper ocean heat anomalies became boldly negative east of the Dateline in the equatorial Pacific Ocean last month. Implied was plenty of support for La Nina ahead. However, the past couple weeks have observed the cool anomalies staring to weaken indicating and La Nina ahead would be brief and weak.

Fig. 1: The 12-week Nino SSTA monitor indicates the recent the cool La Nina-spike weakened slightly last week.

Discussion: Diagnostics in support of a developing La Nina later in quarter 3 of 2020 have eased. Last week the Nino SSTA regions turned slightly warmer after a cool peak earlier this month (Fig. 1). Subsurface cool water required to fuel La Nina developed rapidly in May but is now fading through mid-June (Fig. 2). The air-to-sea link of ENSO is not happening as the cooler waters are not able to drive a positive southern oscillation index (Fig. 3) typically present during La Nina. Implied is any La Nina ahead is likely weak and short-lived.

Fig. 2: Upper ocean heat in the eastern equatorial Pacific Ocean has trended less cool the past couple weeks.

Fig. 3: Positive phase southern oscillation index which is present during La Nina is not developing.