Highlight: Western U.S. drought will shift eastward across the southern states, Black Sea drought shifts southeastward, Australia turns wetter and Paraguay drought worsens.
Fig. 1: The NOAA/CPC soil moisture ranking percentile valid September 2020 with Climate Impact Company annotated 3-month trend.
September 2020 global soil moisture trend: One of the most dramatic signatures is the North America drought which encompasses the western U.S. and eastern Canada (Fig. 1). Regional warm SSTA caused the dryness. The “warm blob” in the northeast Pacific is linked to an upper ridge pattern turning Alaska drier, intensifying the western North America drought and allowing that drought to extend eastward reaching Iowa. Warm SSTA in the western North Atlantic basin once again enabled a summertime upper ridge pattern worsening East Canada to New England drought.
Across Eurasia a late summer upper ridge pattern caused drought to emerge and strengthen in the Black Sea region extending northeastward to Central Russia. Occasionally, an upper ridge pattern extended northward from North Africa to turn France drier. U.K. to northern Europe turned wetter. Probably the most fantastic soil moisture regime entering quarter 4 of 2020 is the widespread wet soils across southern and eastern Asia. The primary contributor to the wet climate in this vast region is anomalous warm SSTA patterns in the Indian Ocean and western Pacific basin.
To the south of the convective rains soaking south and east Asia a drought pattern lingers in far Southeast Asia. In the southern hemisphere, despite a developing La Nina a dry soil regime redeveloped in southwest and northeast Australia. La Nina usually brings a wet climate for Australia. The wet soil regime in southern Asia expanded westward across tropical Africa during late Q3 of 2020.
Finally, drought conditions worsened from Paraguay to central Brazil and northwestward to Venezuela the past several months. A wetter regime was observed across Peru. The southern half of Argentina was much wetter.
September 2020 global SSTA: Global SSTA was much warmer than normal during September 2020 lead by extremely warm SSTA across the Indian Ocean, Western Pacific Ocean and the northeast Pacific where the “warm blob” was 3rd warmest on record (Fig. 2). The western North Atlantic basin was also very warm. The warm SSTA in the Indian Ocean/West Pacific enabled a wet climate causing widespread wet soil moisture. The northwest North Atlantic basin warm SSTA enabled a high pressure ridge that dried out Eastern Canada.
La Nina emerged in September 2020 and in the Indian ocean the warm SSTA is shifting eastward, a sign of a developing negative phase of the Indian ocean Dipole. Departing the southern hemisphere cold season a large area of cool SSTA emerged southeast of Africa. East of Australia a large area of warm SSTA persists.
The Q4 2020 outlook indicates La Nina strengthens and weak -IOD may emerge.
Fig. 2: The global SSTA analysis for September 2020 and primary regions of influence on climate are identified.
Fig. 3: The NOAA/CPC soil moisture ranking percentile valid September 2020 with Climate Impact Company annotated 3-month forecast.
The quarter 4 of 2020 global soil moisture forecast trend: A developing La Nina is a dominant force on the quarter 4 of 2020 global precipitation pattern and influence on soil moisture (Fig. 3). After tropical cyclone season has finished expect the western U.S. drought to expand eastward across the southern half of the U.S. La Nina will cause Southwest Canada and the Northwest U.S. to turn wet.
In South America the La Nina influence is strong and includes a wet pattern ending the northwest South America drought. Also likely is a wet pattern over East Brazil but dryness worsens from Paraguay and vicinity into northeast Argentina to Uruguay. The Chilean drought re-intensifies.
The dry pattern in the Black Sea region to Central Russia eventually eases while the causal high pressure zone shifts south and causes dryness Turkey and eastward. Meanwhile open waters south of the polar vortex enables widespread above normal precipitation across Northern Russia.
The La Nina pattern turns China to Japan much drier – the first dry climate of this year for those regions. However, La Nina will soak Indonesia and Australia to finish 2020.
A weak -IOD pattern will cause East Africa to turn dry.