Discussion: The North Atlantic tropics remain unusually cooler than normal as the onset of the most active part of the tropical cyclone season approaches (Fig. 1). In the main development region (MDR) for hurricanes located between the Caribbean Sea and Cape Verde Islands the daily tropical North Atlantic (TNA) index is -0.82C (Fig. 2). There is essentially no change during the past 30 days implying the monthly TNA index for July would easily be the coolest on record.
Previously, the coolest TNA index for July was observed in 1971, 1972 and 1974 ranging from -0.40 to -0.50. July 2018 may be twice as cool. During 1971, 1972 and 1974 tropical cyclone activity able to reach tropical storm or hurricane intensity was confined to the western North Atlantic basin (Fig. 3-5). There were no “Cape Verde storms” which are typically the strongest hurricanes.
The cool SSTA in the MDR will inhibit hurricane development in 2018. Most of this season’s activity will be in the western North Atlantic basin and threatening both the Gulf of Mexico and U.S. East Coast. Duration of storms is likely limited holding down intensity.
Fig. 1: North Atlantic basin sea surface temperature anomalies for July 25, 2018 provided by Storm Vista WX Models.
Fig. 2: The tropical North Atlantic index is measured in the main development region for North Atlantic hurricanes. The projected July 2018 value is around -0.80 easily the coolest on record.
Fig. 3-5: The tropical cyclone tracks for 1971, 1972 and 1974 provided by Unisys Weather identifying most seasonal activity away from the MDR.