Discussion: Large regions of significant soil moisture change over the past 3 months were evenly split across the globe with both 5 large areas of regional wetter or drier regime adjustments. Beginning in North America a vast area of much wetter than normal soil moisture has developed across Mexico, the central and eastern U.S. and far southeast portions of Canada. The wetter trend is associated with influence of warm SSTA in the southeast Pacific and off the East Coast of the U.S. providing above normal low atmospheric moisture entrained into the upper flow south of a stronger than normal polar vortex in eastern Canada. In west/northwest Canada an upper ridge pattern has persisted northeast of a warming northeast North Pacific. Beneath the ridge pattern Western Canada drought has intensified.
In South America a wet trend centered on Paraguay is also affecting northern Argentina and southwest to central Brazil the past 3 months. Most recent wetter weather has been caused by a stronger than normal polar vortex over or in-between Antarctica and South America. The polar vortex has ejected short wave energy across South America bringing stronger than normal cold fronts into the early summer season some of which have deposited excessive rain in Argentina while stalling once shifting north over Brazil. Interestingly, northeast Brazil has turned wetter in the current pattern.
The mega-drought affecting Europe is mostly related to an issue present nearly all of 2018. The polar vortex across eastern Canada to Greenland and sometimes the northern North Atlantic has been stronger than normal most of this year causing an upper ridge pattern to emerge over Europe and stagnate. The upper ridge has caused persistent dryness and following heat during the summer season which further enhanced drought. The dryness has strengthened during autumn from Central Europe eastward and to the east of the Caspian Sea.
Upper level energy ejected from the persistent upper trough over Eastern Canada to Greenland during the past 3-6 months has turned southeast and caused a wet pattern to emerge in Northwest Africa. The lack of tropical convection in the equatorial portion of Africa is also related to dryness in South Africa where drought is intensifying.
A combination of an emerging positive phase of the Indian Ocean Dipole (+IOD) and general El Nino condition in the tropical Pacific has been the catalyst for a somewhat sharp reversal to drier soil moisture conditions across Southeast Asia and India. However, an active Madden Julian oscillation (MJO) has favored a wetter climate in parts of Indonesia while stronger than normal cold fronts into Australia into the early warm season have caused the strong drought to weaken slightly.