How busy was that hurricane season?

 

2025 Atlantic hurricane season as of October 8 (Source: NOAA)

The total number of tropical storms and hurricanes isn’t always an accurate measure of how busy a hurricane season has been. That’s because a season can have a high number of weak and/or short-lived tropical storms that can inflate the overall number of tropical storms and hurricanes. 

Scientists at Colorado State University have developed a measure that takes this into account. Known as the ACE score (“Accumulated Cyclone Energy”), it takes such factors as storm intensity and duration into account. A longer lasting hurricane, for example, will have a higher ACE score than a short-lived tropical storm.

An “average” Atlantic hurricane season features a total of 14 tropical storms, of which 7 become hurricanes with 3 major hurricanes, according to NOAA. That’s for the 30-year period of 1991-2020. The average ACE score for the same time period is 122.3 knots squared (kn²).

The 10 busiest Atlantic hurricane seasons based on the overall number of named storms is not the same as the 10 seasons with the highest ACE score. That’s a significant illustration of the difference between a season having fewer, more intense and/or longer-lasting hurricanes as opposed to a higher number of less intense, short-lived tropical storms.

For example, the 2017 Atlantic hurricane season had a higher than average number of systems with 17 tropical storms, 10 hurricanes and 6 major hurricanes and finished with an ACE Score of 224.9 kn². The 2020 season had almost double the  number of tropical storms (30), with 14 hurricanes and 7 major hurricanes, but finished with an appreciably lower ACE score of 179.8 kn² due to having more, weaker systems.

Having these two ways to accurately measure how active a given hurricane season is has become especially important in recent decades that have featured an overall uptick in tropical activity. In fact, the 30-year period of 1995 – 2024 has been considerably busier in the tropical Atlantic than the previous 30-year period. While eight of the 10 seasons with the highest number of Atlantic tropical storms and hurricanes have occurred since 1995, only five with the highest ACE score have occurred in the same time period. 

Only three seasons (2005, 1995 and 1933) appear in both top 10 lists for highest number of tropical storms and hurricanes, as well as highest seasonal ACE score. The 2025 Atlantic hurricane season isn’t anywhere near either top 10 list with a total of only 10 named tropical storms, 4 hurricanes and 3 major hurricanes so far this season.

Busiest Hurricane Seasons
By ACE Score (kn2)
Source: Colorado State University		Tropical Storms	Hurricanes	Major Hurricanes
258.3	1933	20	11	6
245.3	2005	28	15	7
231.1	1893	12	10	5
229.6	1926	11	8	6
227.1	1995	19	11	5
226.9	2004	15	9	6
224.9	2017	17	10	6
211.3	1950	16	11	6
188.9	1961	12	8	5
181.8	1998	14	10	3

 

By named storms
	ACE Score (kn2)
2020	179.8	30	14	7
2005	245.3	28	15	7
1933	258.6	20	11	6
2012	132.6	19	10	2
2011	126.3	19	7	4
2010	165.5	19	12	5
1995	227.1	19	11	5
1887	181.3	19	11	2
2024	161.5	18	11	5
2019	129.8	18	6	3

Weather Quiz

 

Hurricane Mitch, October 1998 (Source: NOAA)

What was the strongest Atlantic hurricane on record during the month of October ?

  
A. Mitch (1998)


B. Wilma (2005)


C. Michael (2018)


D. Milton (2024)

A closer look at Atlantic hurricane cycles

 

Sunset at Pine Island Beach, Florida

Although it isn’t over yet, the 2025 Atlantic hurricane season has already done something that hasn’t occurred since 1935. That’s the last time the season’s first three hurricanes each achieved major, Category 3 status. More broadly, the 30-year period in the tropical Atlantic from 1995 – 2024 was busier than average.

An average Atlantic hurricane season has 14 tropical storms, of which 7 become hurricanes and 3 become major hurricanes, according to NOAA. A “major” hurricane has sustained winds of at least 111 mph making it a Category 3 on the Saffir-Simpson Hurricane Wind Scale. An active season or two by itself doesn’t mean very much, just like a quiet season or two doesn’t indicate a trend. That’s why it’s important to look at longer periods of time when trying to determine whether or not a pattern exists. 

The last 30 years, for example, saw an average of 15.8 named tropical storms, 7.8 hurricanes and 3.6 major hurricanes.  That includes at least one Category 5 hurricane every other year. Three seasons in the last 30 years (2023, 2020 and 2005) had at least 20 named tropical storms. Another four had 19 tropical storms (starting in 1995). There have also been several quiet seasons in the last three decades such as in 1997, 2009 and 2013, but those were the exception.

Two shorter periods stand out for different reasons over the last 30 years. A total of eight Category 5 Atlantic hurricanes developed during the five-year period from 2003 – 2007, with a seasonal record of four in 2005. Another 12 Category 5 Atlantic hurricanes have developed since 2016, including Erin and Humberto this season.

By comparison, the 30-year period from 1965 – 1994 was much quieter in the tropical Atlantic with an average of 9.9 tropical storms, 5.3 hurricanes and 1.6 major hurricanes. The busiest season during these three decades occurred in 1969 with 18 tropical storms, 12 hurricanes and 5 major hurricanes. The most infamous hurricane of the 1969 season was Hurricane Camille, which remains one of only four Category 5’s that made landfall in the United States.

Hurricanes don’t have to be major to be high impact. North Carolina hasn’t had a major hurricane landfall since 1996, but has seen multiple lesser hurricane landfalls since then, such as Floyd (1999), Isabel (2003), Irene (2011) and Isaias (2020). Coincidently, these four hurricanes also had significant impacts on the DMV (DC, Maryland and Virginia) after making landfall in North Carolina.

October gets underway

 

An early October day in Washington, D.C.

September 2025 finished as a slightly cooler and drier than average month in the nation’s capital. Despite rainfall on 11 of the final 15 days of September, last month was a drier than average September for the fourth consecutive year.

October is the second of three months of meteorological fall and often features some of the finest weather of the year with mild days and cool, crisp nights. Average daily high/low temperatures in the nation’s capital range from 75°/58° on October 1 to 64°/46° on Halloween.  

DC’s warmest October temperature on record of 98° occurred relatively recently on October 2, 2019. Eight of the last 10 Octobers have been warmer than average in Washington, D.C. Meanwhile, DC’s coolest October temperature of 26° has occurred twice, most recently on October 31, 1917. Temperatures at or below freezing in October are quite rare in the nation’s capital with none since October 20, 1992 (32°).

The nation’s capital averages 3.66” of October rainfall. However, eight of the last 10 October’s having been drier than average. Weakening tropical systems can sometimes impact the D.C. Metropolitan Area in October with heavy rain and severe weather. Such was the case with the remnants of Hurricane Opal in 1995 and post-Tropical Storm Sandy in 2012. The remnants of Tropical Storm Tammy also contributed to making October 2005 the wettest on record in the nation’s capital.

Washingtonians can get an early taste of winter with light October snowfall on occasion. Although the nation’s capital doesn’t see enough October snowfall to produce an average amount, a trace of snow (too little to measure) does occasionally occur, with the most recent being in 2011. The earliest in the fall season the nation’s capital has experienced accumulating snowfall was on October 10, 1979, with 0.3” at National Airport.

NOAA’s Climate Prediction Center expects October 2025 to be a warmer than average month with near average rainfall in the nation’s capital. That would be in contrast to last October that was much drier than average.