Highlights –August 2020
1. Northern Hemisphere
circulation during August featured above-average heights over the North Pole, the
mid-latitudes of North Pacific, the northwestern U.S. and northern Canada, and
below-average heights over the northern North Pacific, western Canada, the northern
North Atlantic, and the Caspian Sea (Fig.
). The main land-surface temperature signals
included above-average temperatures in the western U.S., western Europe, and
most of the high-latitudes of central Russia (Fig. ). The
main precipitation signals included above-average precipitation in the eastern
and southeastern U.S., and below-average precipitation in the western and
central U.S. and southern Florida (Fig. ).
a. North America
circulation during August featured a broad ridge cross the inter-mountain
region of the western U.S. and the central U.S., and a broad trough over eastern
Canada and the eastern U.S. (Fig. ). This pattern contributed to above-average
surface temperatures in the western and central U.S., and to near- or
below-average temperatures in the eastern U.S. (Fig. ).
Also during August,
area-averaged total precipitation in the Southern California, Inter-Mountain, and
Southwestern U.S. regions were less than the 10th percentile of
occurrences, while totals in the Ohio Valley and Mid-Atlantic regions were
larger than the 90th percentile of occurrences (Fig. ).
b. Europe and Asia
height pattern featured a wave pattern with above-average heights in western
Europe and the eastern half of Siberia, and below-average heights over the Caspian
Sea (Fig. ).
This circulation pattern contributed to above-average surface temperatures in
central Russia, with the largest departures (+3.0 to +4.0°C) observed (Fig. ).
Much of the mid-latitudes of Asia and eastern Siberia recorded near-average
surface temperatures. The significant departures were observed in the
low-latitudes of Asia, where some of the region experienced temperatures in the
90th percentile of occurrences.
c. West African monsoon
the west African monsoon extends from June through September, with a peak
during July-September. During August, the west African monsoon system strengthened
in the north and weakened in the south (Figs.
with area-average rainfall totals near the 100th percentile of
occurrences (see Sahel region, Fig. ). In July, this region also recorded
totals near the 100th percentile of occurrences.
2. Southern Hemisphere
The 500-hPa height
field during August featured above-average heights over the South Pole, and a wave-3
pattern in the mid- and high latitudes with above-average centered near 160
75 oW and 10 oE,
and below-average centered near 135 oW, 30 oW
and 75 oE (Fig. ).
ozone hole typically develops during August and reaches peak size in September.
The ozone hole then gradually decreases during October and November, and
dissipates on average in early December (Fig.
). By the end of this August, the size
of the ozone hole was below its 2010-2019 average. Associated with the ozone
hole during this August, the size of the Southern Hemisphere polar vortex and
the areal extent of polar stratospheric clouds were both above- to near-average