Research has shown that when the far eastern equatorial Pacific is cool and near the Dateline in the tropics surface water is warm there is a tendency in the upper air pattern over the subtropical western North Atlantic for a low pressure trough to form. This phenomenon is known as the tropical upper troposphere trough (TUTT). The TUTT pattern produces upper level shear suppressing tropical activity.

Solar Cycle 24 is ending as a new solar minimum arrives as of late 2018 and 2019. Interestingly, NASA forecasts an unusually lengthy solar minimum extending through 2022 and into 2023. Solar minimum usually lasts less than 2 years as part of the complete 11-year solar cycle.

Emergence of phase_1/phase_2 of the Madden Julian oscillation implies increased vertical motion and lowering upper level wind shear in the tropical North Atlantic (where tropical cyclones develop) and tropical Africa (where tropical waves which become Atlantic tropical cyclones develop). The MJO has anchored over Maritime Continent/West Pacific tropics recently certainly contributing to an increase in tropical cyclone activity. However, today’s ECMWF MJO forecast indicates MJO weakens over Maritime Continent and is likely to regenerate over the tropical North Atlantic/Africa in 2 weeks.

A summary of seasonal forecasts of North Atlantic basin tropical cyclone activity issued initially in April and updated in June and August by the Tropical Meteorology Project at Colorado State University, Tropical Storm Risk of U.K. and Climate Impact Company indicate each revision is slightly more active due to less inhibiting upper shear due to a weakening El Nino (compared to early forecasts) coupled with a warmer than normal North Atlantic basin especially just north of the tropics.