“Warm Blobs” Shaping the Southern Hemisphere Early Summer Climate Pattern

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Executive summary: In recent years large areas of warm SSTA commonly referred to as “warm blobs” have emerged as prominent influencers on regional climate. The Northeast Pacific “warm blob” emerging in 2013-14 is the most talked about (and researched) climate influencer but others have emerged. “Warm blobs” are effective climate diagnostics correlating to large regions of semi-permanent high-pressure featuring above normal sunlight and anomalous dry/warm climate. Emergence of “warm blobs” certainly is consistent with the accelerating warming atmosphere of the past decade. To compensate for the “warm blob” to semi-permanent high-pressure ridge areas (in the subtropical and middle latitudes) areas of storm-generating trough(s) are also vividly present. Given the high-amplitude upper air pattern associated with the “warm blob” SSTA pattern slow-moving climate regimes capable of producing harsh conditions such as drought or flooding are generated. In this report, we take a look at the southern hemisphere “warm blobs” and the correlating upper air pattern just ahead of meteorological summer in the southern hemisphere.

Discussion: The “warm blob” SSTA regions near and east of New Zealand and east of Argentina are semi-permanent and dominant features in the southern hemisphere SSTA regime (Fig. 1). However, relatively new “warm blobs” have recently emerged off Southwest Africa and in the South Indian Ocean. In fact, ahead of summer, the “warm blobs” off Southwest Africa and particularly in the South Indian Ocean are strengthening most quickly (Fig. 2). The correlating “warm blob” SSTA regions to the upper-level semi-permanent high-pressure ridge areas in the southern hemisphere is striking! The strongest high-pressure ridge areas are across/near the South Indian Ocean and New Zealand “warm blobs” (Fig. 3). High-pressure ridging is also intense to the east of Argentina.

Fig. 1:  Daily global SSTA analysis for Nov. 27, 2021 identifying the southern hemisphere “warm blobs” just-ahead of meteorological summer 2021-22.

Fig. 2:  Southern hemisphere SSTA changes over the past 30 days.

Fig. 3:  The November 2021 semi-permanent high-pressure ridge areas across or near “warm blob” SSTA regions (and compensating upper trough locations).

Beneath high-pressure areas sunlight is above normal and a feedback mechanism develops as increased sunlight generates stronger warm SSTA which in-turn maintains/strengthens high-pressure ridging. Often less-discussed is the downstream compensating effects. For instance, note that in-between the South Indian Ocean and New Zealand upper-level ridge areas a compensating upper trough is located over Australia and responsible for bringing drenching rains during late spring. Additionally, just north of the high-pressure region to the east of Argentina a semi-permanent upper trough has generated and responsible (in-part) for bringing significant rains to parts of South America during mid-to-late spring.

The ECMWF global SSTA forecast for January 2022 indicates that during mid-summer in the southern hemisphere “warm blobs” will strengthen (Fig. 4). Consequently, attendant semi-permanent high-pressure centers are also likely to intensify. ECMWF upper air forecast for January 2022 projects further amplification of the New Zealand high-pressure ridge which extends eastward across the South Pacific subtropics (Fig. 5). Additionally, the South Atlantic “warm blob” intensification is well-correlated to an amplified high-pressure ridge in that position. Of interest is the compensating upper trough(s) which are weaker during summertime but located over east-central South America and Australia. Presence of the weak upper trough patterns increases risk of wet mid-summer climate most likely for east/north Australia and East Brazil certainly defeating any drought scare but adding to the risk of gully-washer mid-summer flooding rainfall risk.

Fig. 4:  ECMWF global SSTA forecast valid January 2022 indicates southern hemisphere “warm blobs” persist.

Fig. 5:  ECMWF upper air forecast for January 2022 in the southern hemisphere.

Conclusion: La Nina is present and developing and forecast to peak in January 2022. However, ahead of meteorological summer in the southern hemisphere presence of large “warm blob” SSTA regions are likely most prominent in shaping the summer time climate pattern. Included are “warm blob” SSTA regions southwest of Africa, in the South Indian Ocean, near and east of New Zealand and also east of Argentina. Each “warm blob” has strengthened during November and according to ECMWF further intensification is forecast by mid-summer. The “warm blobs” are well-correlated to high-pressure ridge areas also forecast to strengthen across and downwind from each “warm blob” region. To compensate for each high-pressure ridge, weak upper trough(s) capable of producing flooding rainfall are forecast (by ECMWF) over Southern Brazil and Australia for mid-summer. The primary concern for Australia and South America during mid-summer 2022 is risk of gully-washer flooding rainfall which should restrict mid-summer drought risk.

Summary: Climate Impact Company continues to stress recent emergence of warm SSTA regions outside of the tropics commonly referred to as “warm blobs” and their influence on the regional (and hemispheric) climate patterns which are as important as the influence of ENSO. The character of climate patterns associated with “Warm blobs” is slow-moving and therefore more impactful.