Once Again…Very Warm SSTA Emerges During Summer Correlated to Current and Additional Super Heat/Dryness
Fig. 1: A rapidly emerging warmer-than-normal ocean surface in the middle latitude/subtropics of the southern hemisphere.
Discussion: During recent mid-to-late summer seasons in both hemispheres a tendency for unusually warm SSTA have developed in the subtropics to middle latitudes. The warmth is emerging due to stronger-than-normal subtropical high pressure ridge areas which typically are located in broad regions of clear sky enabling plentiful sunlight to warm the ocean surface.
The warmer-than-normal ocean surface acts as a feedback to the upper atmosphere by causing the already associated strong subtropical ridge to increase amplification. The result on weather across continental areas is increased risk of sustained late summer anomalous heat and dryness. Drought conditions worsen and sometimes flash drought can generate.
During January 2019 (so far) the warm SSTA regions and correlation to mid-atmospheric high pressure ridging is easily recognizable over Australia (Fig. 2) and South America (Fig. 3). Beneath the upper ridge unusually hot and dry weather has affected southwest and southeast portions of Brazil while Australia is about to have their hottest January on record.
Fig. 2: The January 500 MB ridge pattern across Southeast Australia is responsible for producing a projected hottest January on record for the continent.
Fig. 3: Searing heat and drought has affected parts of southwest and east/southeast Brazil beneath an amplified upper ridge pattern in January.