How Does this Hurricane Season Compare ?

 

Saffir-Simpson Hurricane Wind Scale (Source: WUSA9)

June and July are two of the quietest months of the Atlantic hurricane season.  There were only three relatively short-lived tropical storms so far this season.  Not since 2017 has the Atlantic come to the end of July without even a single hurricane.  The tropical Atlantic doesn’t usually get busy until the middle of August ahead of the peak of the season in September.  September is when atmospheric and environmental conditions are the most favorable for tropical storm and hurricane development. 

It may seem strange that this season hasn’t had the overall number of named storms by the end of July that recent seasons have had.  Hurricane Barry developed in July 2019, while nine named storms developed through the end of July 2020.  Five named storms developed by this point last season. 

However, in spite of the rapid starts to the previous three hurricane seasons, including the highest overall number of named Atlantic storms in 2020 (30), none of the last three seasons rank among the top 10 based on the seasonal total of Accumulated Cyclone Energy (ACE).  Scientist’s use the ACE Index to gauge how active a hurricane season is based on such factors as storm intensity and duration, as well as the overall number of days with an active tropical storm or hurricane.  One long-lasting, major hurricane could generate more ACE than several weaker and/or short-lived tropical storms.

The 2020 Atlantic hurricane season with an eye-popping total of 30 tropical storms is a good example.  Of those 30 named storms, 11 lasted three days or less and were relatively weak.  That’s not to say a tropical storm or minimal hurricane can’t be destructive or deadly, but the overall number of named storms itself is an artificial measure of how busy a season is.  The 30 tropical storms (that included 14 hurricanes) in 2020 produced a total of 118 days with at least one active tropical storm and a seasonal ACE score of 179.8.

By comparison, the 2017 hurricane season had 17 tropical storms (with 10 hurricanes) for a total of 93 days with at least one active tropical storm. However, since the 2017 hurricane season had 19.25 days with an active, major hurricane (Category 3/+ with sustained winds of 111/+ mph) compared to only 8.75 days in 2020, 2017’s seasonal ACE score was much higher at 224.9.  That made 2017 the Atlantic’s seventh most active season based on its ACE score.  Despite its 30 named storms, 2020 ranked as only the 13^th most active season given its ACE store due to its higher number of weaker storms.

It remains to be seen whether 2022 will end up more like the 2017 or 2020 seasons.  NOAA will issue the early August update to its seasonal hurricane forecast in the next week. 

Weather Quiz

 

True or False.

Two of D.C.’s five wettest July’s have occurred since 2017.

Dangerous July Severe Weather Outbreaks

 

Photo Credit: Robin Beal

Although less common than in April, May or June, the D.C. Metro Area has seen its fair share of severe weather in July.  Thunderstorms have been a fairly regular occurrence so far this month, which has been especially rainy.  Given the severe weather potential the next few days, here are a few memorable July outbreaks in recent years.

2022: The D.C. Metro Area had a very busy severe weather day on July 12.  Following a typical July afternoon with highs in the 90s and dewpoints in the low 70s coupled with a high degree of atmospheric instability, there were multiple severe wind and hail reports between 4:00 p.m. and 9:00 p.m.  This outbreak came a week after another outbreak that included two tornadoes.  One tornado touched down in Bowie, Maryland and another occurred in Anne Arundel County, Maryland.  Fortunately, power outages were minimal and no fatalities were reported.

2021: Two confirmed tornadoes occurred within D.C. city limits on July 1.  An EF-0 with winds of approximately 80 mph occurred near the U.S. Capital.  A second tornado developed in Arlington and tracked across the Potomac into D.C.  It was an EF-1 with peak winds of 90 mph during its 4.4-mile path.  In addition to the tornadoes, what made this severe weather memorable is how two separate rounds occurred.  The first round of severe weather was during the peak heat of the afternoon and the second occurred between 9:00 p.m. and 10:00 p.m. when the tornadoes developed. 

2017:  Several rounds of thunderstorms brought severe weather and flash flooding to parts of the D.C. Metro Area from July 22 - 24.  The most significant occurred in Queen Anne’s County in Maryland on July 23.  An EF-2 tornado was on the ground from 1:29 am to 1:33 am, with peak winds of 125 mph.  Although the tornado caused appreciable damage to the towns of Bay City and Stephenville, Maryland, no fatalities occurred.  A total of 2.37” of rain occurred at National Airport during this 3-day span.

2010:  A significant heat wave was capped off on July 25 with highs near 100° and an unstable atmosphere.  That’s when a squall line developed west of town and came through the Nation’s Capital with multiple severe wind gusts.  These storms produced a slew of downed trees and power lines and resulted in widespread power outages, especially in densely populated Montgomery County, Maryland.

A thunderstorm becomes “severe” when it contains one or more of the following: wind gusts of at least 58 mph, hail 1” in diameter or greater, or a tornado.  While heavy rain and lightning don’t make a thunderstorm “severe” per se, all thunderstorms are potentially dangerous and should be taken seriously.