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A quick blink and it was easy to miss a weekend tropical storm that was barely felt even by those living in Myrtle Beach where it made landfall.
Tropical Storm Colin was so short, that the first advisory was issued Saturday morning when the center was already 13 miles ashore of South Carolina. Later that night it weakened to a tropical depression and dissipated over eastern North Carolina, lasting only 24 hours as a named system.
These typically weak and brief storms lasting less than two days are called “shorties” and they are suddenly becoming very routine.
Colin follows a pattern, behind Bonnie which was named just hours before landfall in Nicaragua and Alex which had a brief spin-up east of south Florida lasting a little over 30 hours.
The 2021 season had nine shorties the most on record in a single season.
Climate change is not causing more storms. The numbers are up because more are being detected.
Storms weren’t always spotted with such precision but the recent innovations in weather geostationary and low-earth orbiting satellite imagery have boosted numbers.
In the case of Colin, forecasters at the National Hurricane Center used radar in space called a scatterometer to detect a small area of surface winds that met the 40 mph threshold for a tropical storm.
These innovations have led to a dramatic increase in shorties over time.
Meteorologist Chris Landsea, discovered that weak, short-lived named storms occurred only about once a year up until the 1920s and about three per year from the 1930s to the 1990s. The numbers began increasing to around five per year since 2000.
The frequency that previously would have been unaccounted for has resulted in a skewed sense of activity. Ranking a season based on the duration and intensity of tropical cyclones provides a clearer picture of the year’s activity. This is accomplished using the Accumulated Cyclone Energy or ACE index.
ACE compares apples to apples by measuring the overall energy or activity from one year to the next.
Last year’s season scored an ACE of 145, about 18 percent above average and while 2020, broke the record for named storms, overall ACE activity only ranked the 13th most active.