| The Northern Hemisphere circulation
featured several persistent anomalies during May (Figs. E10,
E12, E13), including
above-average heights at 500-hPa over the northern and eastern North Pacific, eastern
Canada, and the eastern North Atlantic, and below-average heights over Alaska, the central
North Atlantic and western Russia. Over North America the anomalous circulation
contributed to significantly above-average surface temperatures over the western United
States and eastern Canada, and to below-average temperatures across Alaska (Fig. E1). Above-average surface temperatures were
also observed over much of Europe and central Russia during the month. The anomalous
circulation also contributed to a continuation of below-average rainfall and excessive
long-term rainfall deficits across Florida and portions of the Gulf Coast (Fig. E3, E5). Elsewhere, above-average
rains were recorded during May in southern China, southeastern Asia, and western Russia (Figs.
E3, E4). 2. Southern
Hemisphere
The primary Southern Hemisphere surface
anomaly during May reflected significantly below-average rainfall across the eastern half
of Australia, with totals in many locations dropping below the 10th percentile
(Fig. E3, bottom). This dryness was partly associated with
anomalous upper-level convergence (Fig. T23) and sinking
motion in the region upstream of the mean midlatitude trough (Fig.
E16), which was situated along the east coast of the continent and spanned both
the middle and subtropical latitudes. The dryness in northeastern Australia (Fig. E4) was also associated with an overall northward shift
in the primary region of tropical convection to well north of the continent (Fig. T25). |
