The 2021 northern hemisphere accumulated cyclone energy index (ACE) is about 75% of normal so far in 2021. Only the North Atlantic basin ACE index is above normal at 79.2 (29% above normal). Interestingly (and rare), both the northeast and northwest Pacific basins have observed below normal ACE index for the tropical cyclone season so far in 2021.

During the past 7-10 days the subsurface east-central equatorial Pacific Ocean has turned sharply cooler. Compared to last year, the amplitude of the cool signature this year is stronger than last including a less warm subsurface West Pacific in 2021. The NCEP CFS V2 identifies the cooler subsurface and applies the cooler regime to the forecast and the result is a stronger La Nina developing during quarter 4 of 2021.