The October 2021 temperature anomaly outlook is ferocious warm Central and into the East. The GFS ENS is super warm east of the Continental Divide for most of the next 15 days and the remainder of October is likely to feature very little change. The West will cool-down and impressively so during the medium-range. However, the eastern 2/3 of the U.S. may receive a record warm mid-autumn.

The wet influence of negative phase Indian Ocean Dipole on Australian climate, particularly across southern areas is fading. However, a persistent La Nina climate may strengthen during quarter 4 of 2021 enabling more wet climate particularly for north and east portions of the continent.

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.