El Niño Outlook for September 2021
Articles by Ryan Truchelut
Two factors have strongest historical relationship with late season tropical activity: Atlantic SSTs, and El Niño/La Niña state in the Pacific. Both Atlantic and Pacific support an extended hurricane season in fall 2021, but are fortunately not as favorable as they were in heading into late 2020.
WeatherTiger’s August Atlantic hurricane season outlook is out now. It continues to call for an active season, with most likely ACE ~50% above normal. Analogs suggest steering may favor elevated U.S. and Florida landfall risks in October. Overall: get ready. Tropical go-time is almost here.
True neutral ENSO conditions are in place in the Pacific, with SST anomalies in the Nino3.4 region drifting around zero in June and early July. Continued neutral or cool-neutral conditions are likely through the summer, and it is now clear that a new La Nina will not develop in time to influence the peak of U.S growing season.
WeatherTiger’s expectations for the 2021 hurricane season shifted higher over the last two months, but remain shy of last spring’s (accurate) prediction for a hyperactive 2020. The most likely outcome is tropical activity around 40% above the average hurricane season.
While the 2020-21 La Nina has not officially ended, observations show that the
central Pacific SSTs have reverted to near normal over the last few weeks, bringing
the event to at least a temporary end. Neutral ENSO conditions are likely to persist
through early summer.
Atlantic Hurricane Season First Look for April 2021 by Dr. Ryan Truchelut – issued 9 April 2021 Key Points WeatherTiger’s first look at the…
WeatherTiger’s first look at the 2021 hurricane season is for a 35-40% chance of a near normal year, with a 30-35% chance of below normal and 30% chance of above normal cumulative activity. The median of our forecast for 100% of average hurricane season activity, or around 15 named storms, seven hurricanes and three major hurricanes.
A La Nina event is quickly weakening in the Pacific, and an upcoming westerly wind burst is likely to restore ENSO neutral conditions by early May. Our ENSO Whisperer April output forecasts that cool-neutral conditions are most likely to persist into the summer months, but redevelopment of a weak La Nina or emergence of a weak El Nino are both realistic possibilities based on both our modeling and current conditions in the Pacific.