Comments on the 2020 North Atlantic Tropical Cyclone Season

Comments on the 2020 North Atlantic tropical cyclone season

Fig. 1: The highest seasonal accumulated cyclone energy (ACE) index values from 1950-2020 identifies 2020 as 9^th strongest.

Discussion: Thirty tropical storms in 2020 across the North Atlantic basin breaks the record of 28 set in 2005. The number of hurricanes (13) and intense hurricanes (6) was slightly below the 2005 record (15 and 7 respectively). Surprisingly, despite the number of events in 2020, the accumulated cyclone energy (ACE) index was 179.7 ranking 9^th highest in the 1950-2020 climatology (Fig. 1). Compared to the 50-year normal, the 2020 season (Fig. 2) was MUCH ABOVE normal for number of events, intense events and ACE Index (Table 1).

Fig. 2: The NOAA preliminary seasonal tropical cyclone activity tracks for the 2020 season across the North Atlantic basin.

 Table 1: The North Atlantic basin tropical cyclone season for 2020 observed tropical cyclone activity versus 50-year normal. Data is provided by the Tropical Cyclone Project at Colorado State University.

One revelation regarding seasonal predictors was recent research identifying early season mid-level relative humidity/precipitable water as an indicator to the activity level and most intense storm location. The MAY/JUN 2020 mid-level precipitable analysis revealed exceptional high-water content in the middle atmosphere across the Gulf of Mexico and off the West Coast of tropical Africa (Fig. 3). During the core of the season (AUG/SEP/OCT) the high level of mid-atmospheric water content expanded and intensified in the western North Atlantic basin contributing to the record number of land-falling events and the outer North Atlantic basin where most storms are born (Fig. 4).

Fig. 3: The mid-level moisture across the North Atlantic basin is an excellent predictor of tropical cyclone season intensity ahead. The MAY/JUN 2020 analysis indicated extremely moist mid-atmospheric conditions across the Gulf of Mexico and off the tropical West Coast of Africa.

Fig. 4: The core of the tropical cyclone season (AUG/SEP/OCT) mid-level atmosphere moisture was abundant for the western and eastern North Atlantic basin.