SSTA Pattern Heading Toward Neutral ENSO

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The February MJO had a profound influence on the environment of the equatorial East Pacific. The (MJO) event shut-down trade winds which eased the up-welling of cool subsurface water to maintain La Nina intensity.

Discussion: During February the most robust signature of the convection phase of the Madden Julian oscillation (MJO) of 2021 (so far) emerged in the equatorial West Pacific expanding to near the Dateline (index_2/index-3/index_4). This (tropical) event (Fig. 1) contributed to the arctic outbreak into Texas. Additionally, the MJO had a profound influence on the environment of the equatorial East Pacific. The event shut-down trade winds which eased the up-welling of cool subsurface water to maintain La Nina intensity (Fig. 2). Coincidentally, the southern oscillation index (SOI) has gone into negative phase since Feb. 24 (a sign that the La Nina climate is weakening). Additionally, the influence of the MJO forced some warming in the subsurface off the northwest coast of South America while waters now east of the Dateline in deeper waters have also warmed and shifted eastward (Fig. 3). The February multi-variate ENSO index (MEI) indicates a steady moderate-strength La Nina climate weakened slight (Fig. 4). Additional weakening of the La Nina climate is likely during quarter 2 of 2021. Although neutral ENSO is ahead for quarter 2 of 2021 forecast confidence for ENSO phase the second half of 2021 remains below average as a returning La Nina cannot be ruled out.

Fig. 1: MJO intensity and location plot for February indicates strengthening mid-to-late month for index two through 4 which represents the equatorial West Pacific to the Dateline.

Fig. 2: The 12-week Nino SSTA regions indicate a choppy decline in the cool La Nina signature.

Fig. 3: The equatorial Pacific subsurface temperature anomalies remain cool in the East Pacific while the warmth in the West Pacific is strengthening and expanding eastward below 100 meter depth.

Fig. 4: The multivariate ENSO index is a measure of the influence on the atmosphere of the Nino SSTA pattern. La Nina climate has started to weaken in February.