2021 Atlantic hurricane season

Another extremely active season expected

The extremely active 2020 Atlantic hurricane season burned through the alphabet with 30 named storms including 14 Hurricanes and 7 Majors.

The two seasonal hurricane forecasts that I trust the most are from Colorado State led by Dr. Phil Klotzbach and NOAA’s Climate Prediction Center. Both of these outfits have a long track record of accuracy, experience, and transparency.

Colorado State

17 Named Storms, 8 Hurricanes, 4 Major Hurricanes, ACE = 150

NOAA Outlook

13-20 Named Storms [Ana through Victor]

6-10 Hurricanes, 3-5 Major Hurricanes, ACE = 110% - 190% of median (130)

Historical Context of 2020 Season

In 2020, the Accumulated Cyclone Energy (ACE) amounted to about 185 units — a metric of storm and seasonal activity that combines intensity and duration. It’s pretty simple to calculate ACE: take the advisory wind speed squared and add it up 4-times per day. The easiest example is a Category 3 Major Hurricane at 100-knots for 1-day = 4 units of ACE. A tropical storm at 35-knots for 1-day has only 0.49 units of ACE. More intense storms will run up the ACE especially the monster open-ocean major hurricanes on a 10-day course from the coast of Africa and around the Bermuda high.

The 2021 seasonal forecast from CSU = 150 and NOAA = 140-250.

Over the past 50-years, the Atlantic basin has transitioned from an inactive-era to an active-era exactly in 1995. Indeed, the mean ACE between the two periods has doubled from 68 to 135. There are various theories for the change in Atlantic hurricane activity including the Atlantic Multidecadal Oscillation (AMO) and the reduction of aerosols against the backdrop of anthropogenic global warming. When will the AMO cycle soon shift back to a colder-state with inactive hurricane activity? I’d lean toward 2030.

Next 7-days

No tropical storm activity is expected in the Atlantic. That’s no surprise considering it’s early June and climatologically we do not see much activity — even in extremely busy season.

Week 2

Looking at the ECMWF Ensembles toward mid-June, there is a hint of activity in the Gulf of Mexico. Here, the ocean temperatures are plenty warm but the wind shear is typically high so any storms are lopsided and difficult to develop.

Development chances of something — a named storm — probably in the 10-20% range at this point. We’ll have plenty of time to watch the storm-happy GFS model and its ensembles. The 2021 season will have two fully comparable ensemble systems from ECMWF and NOAA for medium-range hurricane forecasting. Finally.

Weather models posted here are from a subscription service mainly for professionals aptly named Weather Models that costs about $10/month on an annual basis. Of course there are many free sources on the web today, but I would be flying blind without access to the best of everything.

Updates Ahead

I’ll be updating this Newsletter every day until the end of the hurricane season. I have yet to figure out the schedule. But, I have plenty of other weather and climate related topics to get into while we wait for hurricane season to heat up — and it certainly will.