El Niño conditions continue this summer but not for much longer. The June Niño 3.4 index (the primary ENSO measurement) was 0.6°C above the long-term average (El Niño is present when the average sea-surface temperatures across the central & eastern tropical Pacific are 0.5°C or greater over an extended period of time). The Climate Prediction Center is forecasting ENSO-neutral conditions to resume within the next month or two as the tropical Pacific cools (see Fig. 1). Over the past month, there has been a gradual decrease in equatorial Pacific sea-surface temperature anomalies (see Fig. 2). What are ENSO-neutral conditions? ENSO-neutral conditions are when neither El Niño or La Niña conditions are present.
The state of ENSO is very important in the evolution of tropical activity across both the Atlantic and Pacific Basins. El Niño acts to suppress tropical activity in the Atlantic Basin. The reason for the suppressing of tropical activity in the Atlantic Basin is due to enhanced vertical wind shear (see Fig. 3). What is vertical wind shear? This is the changing of wind speed and direction from around 5,000 feet to 35,000 feet above the ground. Wind shear is not good for tropical cyclogenesis because the shear can act to rip apart a developing hurricane and/or prevent a tropical wave from developing any further.
With El Niño expected to diminish within the next month or two, it is possible the Atlantic Basin will become active if the atmosphere responds in time to the ENSO-neutral conditions. Climatologically, ENSO-neutral and La Niña tropical seasons are more active than El Niño season (see Fig. 4).
Keep in mind, hurricane season runs from June 1st through November 30th–leaving plenty of time for tropical activity to become enhanced. It should be noted, the peak of hurricane season is August through September in which El Niño conditions will likely continue through the climatologically busiest period. It looks like the hurricane season will become more active as we head into a more climatologically active period paired with the development of ENSO-neutral conditions. Other factors can and do influence tropical activity such as the strength of the west African monsoon and the sea-surface temperatures across the Atlantic Basin.
Christopher Nunley is Meteorologist on Firsthand Weather, Lecturer in the Department of Geosciences at Mississippi State University (MSU), and a PhD Candidate (Earth and Atmospheric Sciences) at MSU. He earned his M.S. in Applied Meteorology at MSU, was an Assistant Cross Country Coach and taught at the University of North Texas, and was a Broadcast Meteorologist at KTEN-TV (just north of Dallas, Texas). Christopher’s main focus lies within teaching and inspiring prospective meteorology students, atmospheric research to further our understanding of atmospheric processes, and forecasting and analyzing extreme weather events to help save lives!