North Atlantic Tropics/Subtropics SSTA Trending Cooler

ALL CLEAR for now. All seasonal TC forecasts are issued.

Table 1: The FINAL 2021 North Atlantic basin tropical cyclone season activity forecasts from Climate Impact Company, Colorado State University, Tropical Storm Risk U.K. and NOAA.

Discussion: All seasonal forecasts for the North Atlantic basin 2021 season are available. The forecasts are in reasonable agreement on above normal seasonal activity. The Climate Impact Company forecast is least active particularly with the accumulated cyclone energy index. Last year, the ACE index was 180. This year the ACE index ranges from 106 to 150. Implied is not nearly as many U.S. landfalling storms as last year. However, risk of at least one land-falling major hurricane in the Gulf of Mexico and on the East Coast is above normal.

The North Atlantic SSTA analysis reveals why the seasonal CIC forecast is slightly lower than other forecasters. The tropics and subtropics have cooled to near or below normal during late spring (Fig. 1) and continue to cooldown. A cooler regime in the deep tropics would lower hurricane/ACE index values.

Fig. 1: The current sea surface temperature anomalies across the North Atlantic basin.

Fig. 2: Morning satellite view of the North Atlantic basin.

Currently, the North Atlantic basin is ALL CLEAR. The upper-level shear pattern has strengthened the past 24 hours. In the extended-range, forecast models are less certain that a tropical cyclone in the Gulf of Mexico will develop. A wet pattern is projected for the medium-range in the Gulf of Mexico but tropical cyclone risk has lowered. Meanwhile the ITCZ in the outer tropical North Atlantic is ahead of schedule.