Late season heat in Iowa last week coupled with deep layer soil moisture deficit over the northern state and widespread soil moisture deficts in the shallow soil moisture produced a borderline flash drought episode. Deep layer soil moisture deficits are spread across the North-central U.S., western Great Plains and Southeast U.S. Fortunately, early autumn cool weather and likely a wet regime in the Southeast eases additional flash drought risk.

La Nina climate is most profound during the cool season. In 2020 a moderate La Nina is forecast to begin in late quarter 3. Since the mid-to-late 1990’s three separate weak-to-moderate La Nina episodes have occurred: 2000, 2007 and 2016. A simple average climate pattern of those 3 analog years for SEP/OCT and NOV/DEC is issued for North America, Europe, South America and Australia.

Research (AMS/Journal of Climate 2/15/18) has shown one of the key predictors of increased North Atlantic tropical cyclone activity since 1995 is the increased mid-atmospheric relative humidity at the onset of tropical cyclone season. Right now mid-atmospheric RH is buoyant in the Bahamas and especially the main development region for North Atlantic hurricanes to the east of the Caribbean Sea. Once the Saharan dust clouds fade (possibly beginning later this week) an uptick in deep tropics systems should emerge.