Extratropical Highlights - August 2026

 

1. Northern Hemisphere

The 500-hPa circulation during August featured widespread above average height anomalies with a maximum over the Baffin Bay and a trough over the East Siberian Sea (Fig. E9). The main land-surface temperature signals include above average temperatures across Eurasia and most of North America (Fig. E1). The main precipitation signals include above average rainfall across northern Alaska and the northern reaches of the European Plain and below average precipitation across southern Europe and the U.S. Gulf Coast region (Fig. E3).

 

a. North America

The 500-hPa height anomalies across North America were predominantly near normal to slightly above average, with a strong maximum centered over the Baffin Bay (Fig. E9). Temperatures reached the warmest 90th percentile of occurrences across most of the contiguous U.S. (Fig. E1). Drier than average conditions were recorded across southern Alaska and the U.S. Gulf Coast region, where many locations reached the driest 10th percentile of occurrences and above average precipitation was recorded across northern Alaska and the U.S. Great Lakes region (Figs. E3, E5, E6).

 

b. Europe and Asia

The 500-hPa height pattern across Eurasia featured predominantly near normal and slightly above average anomalies (Fig. E9). Widespread above average temperatures were recorded across Europe and Asia with most of Europe recording values in the warmest 90th percentile of occurrences (Fig. E1). Southern Europe recorded drier than average conditions with many areas reaching the driest 10th percentile of occurrences, and northern Russia recorded above average precipitation with areas in the European Plain reaching the wettest 90th percentile of occurrences (Fig. E3, E4).

 

c. West African monsoon

The West African monsoon extends from June through September, with a peak during July-September. During August 2026, the west African monsoon system recorded predominantly below average rainfall totals across the Sahel region (Figs. E3, E4).

 

2. Southern Hemisphere

The 500-hPa circulation featured a wavetrain pattern with alternating centers of above and below average height anomalies (Fig. E15). The main land-surface temperature signals were above average temperatures in parts of South America, southern and eastern Africa, and south-eastern Australia (Fig. E1). Northeast Australia recorded below average precipitation totals during the month of August and Northeast Brazil continues to record below average precipitation (Figs. E3, E4). Southeastern South America and Southern Africa recorded above average precipitation totals (Figs. E3, E4).

 

a. The ozone hole

The Antarctic ozone hole typically develops during August, reaches its maximum extent during September, and then gradually decreases through October and November before dissipating, on average, in early December (Fig. S6). During late August 2026, the ozone hole underwent rapid expansion and reached approximately 20 million square kilometers, near the 2015–2024 average, before increasing to above-average size in early September (Fig. S6). Ozone-hole development is favored by a strong, persistent polar vortex and extensive polar stratospheric cloud (PSC) formation. By the end of August, the 2026 Southern Hemisphere polar vortex area was slightly above the 2015–2024 mean but remained within the historical range. In contrast, PSC area was substantially above average during much of late July and August and has exceeded the 2015–2024 range (Fig. S6).