Sweating through late summer

 

A stellar late-summer day in DC

Although no more heat waves are expected this month in the nation’s capital, there have been some memorable late August heat waves. Some have occurred recently.

2024: This was DC’s third hottest summer on record. Record-setting triple-digit heat occurred on August 28. That’s when the high temperature climbed to 101° as part of a four-day heat wave through August 29. A “heat wave” is loosely defined as three or more consecutive days of 90-degree heat. Not only was that a daily record high for Washington, D.C., but was also DC’s first instance of triple-digit heat during the final 10 days of August since 1987.

2018: This was one of the rare summers that August was warmer than July in the nation’s capital. August ended with a notable late-season heat wave with highs in the 90s on five consecutive days (August 27-31). The hottest day was August 29 with a high/low temperature of 94°/79°. While no record highs were set, record high-low temperatures were set on three consecutive days (August 29-August 31). That means the daily low temperature remained unusually warm.

2010: This summer finished as DC’s hottest on record and included four days of triple-digit heat. August 2010 ended with an unusual heat wave that lingered into September. DC’s average daily high/low temperatures were 94.5°/73.3° between August 29 and September 3.

1998: This August was DC’s hottest month of the year for the first time since 1984. Ironically, the hottest weather of the month didn’t occur until the final third of the month. Nine of the final 10 days saw 90-degree heat in the nation’s capital. A record-tying high temperature of 97° occurred on August 25. 

Hurricane Andrew: A look back

 

Hurricane Andrew, August 1992 (Source: NOAA)

“Andrew” will forever remain in infamy among Atlantic hurricanes. Monday, August 24 will be the 34^th anniversary of Hurricane Andrew’s landfall in south Florida as a Category 5 hurricane with sustained winds of 165 mph leaving unspeakable devastation in its path.

Hurricane Andrew was the costliest natural disaster in U.S. history at the time and caused roughly $60.5 billion in damages (2024 dollars). Andrew had a relatively compact size and fast rate of speed as it traveled across south Florida. Its track south of Miami near Homestead, in combination with its relatively small wind-field (circumference of hurricane force winds), largely spared downtown Miami any significant impacts. That was fortunate since Andrew could have caused even more casualties than the 65 fatalities that occurred had its past moved northward.

Hurricane Andrew occurred prior to the very active 1995 Atlantic hurricane season that represented a return to an active Atlantic hurricane cycle that’s continued ever since. Prior to that, during the bulk of the 1970s through the early 1990s, the tropical Atlantic experienced many below average hurricane seasons.

When Andrew made landfall as a Category 5 hurricane in 1992, it became only the third on record at the time to make landfall in the United States (along with the 1935 Florida Keys storm and Hurricane Camille in 1969). Not only was Hurricane Andrew significant for its rare intensity at time of landfall, but also for when it occurred. Florida’s coastal development and population had increased significantly since the 1970s and 1980s when there were few direct impacts from tropical cyclones.

Parallels exist between the 1992 Atlantic hurricane season and this season. A strong episode of El Nino helped suppress hurricane development during the 1992 season. The current episode of El Nino is expected to be even stronger than that one was. Consequently, NOAA expects this to be a below average hurricane season.

El Nino’s impact on the hurricane season

 

Hurricane Joaquin, October 2015 (Source: NOAA)

NOAA recently issued a statement saying a very strong El Nino event is likely during the upcoming fall and winter in the Northern Hemisphere. That could have profound effects on the Atlantic hurricane season and is reflected in NOAA’s forecast for a below average season.

Since 1950, there have been three separate “very strong” episodes of El Nino that led to a seasonal average of seven tropical storms, three hurricanes and only one major hurricane. That’s compared to the normal seasonal average of 14 tropical storms, 7 hurricanes and 3 major hurricanes. The current hurricane season could mirror one of these three prior seasons that also had a “very strong” episode of El Nino.

2015-2016 (2015): The 2015 Atlantic hurricane season was below average with only 11 tropical storms, 4 hurricanes, including 2 major hurricanes. The strongest storm this season was Hurricane Joaquin in late September and early October. It reached peak intensity on October 1 as a borderline Category 4/Category 5 storm with peak sustained winds of 155 mph. However, the only storms to make landfall in the United States that season were Tropical Storms Ana and Bill.

This season’s ACE score was only 62.7 and while relatively high for an El Nino season, still much lower than the seasonal average ACE score of 123 10⁴ knot² (1991-2020). The ACE score is a more accurate measure of how busy a season is than just the overall number of named storms. It takes into account the number of tropical storms and hurricanes, as well as the intensity and duration of the storms.

1997-1998 (1997): This season had a particularly strong El Nino. There were only 8 tropical storms, 3 hurricanes and 1 major hurricane. The strongest hurricane of the season was Hurricane Erica that peaked at Category 3 intensity (125 mph sustained winds) over the open Atlantic. Erica was the only named storm in the Atlantic in August or September. 1997’s final ACE score – a measure of tropical storm and hurricane intensity and duration – was 41.

1982-1983 (1983): Since the majority of the 1970s and 1980s saw below average Atlantic hurricane seasons, the 1983 season didn’t stand out as much at the time. It occurred during another very strong episode of El Nino and had only 4 tropical storms with 3 hurricanes and 1 major hurricane. The major hurricane was “Alicia.” A Category 3 storm, Alicia developed off the Texas Gulf Coast where it made landfall. Major impacts occurred in Houston and it was the costliest hurricane in U.S. history at the time. The 1983 season, as a whole, however, was exceptionally quiet and had an ACE score of only 17.4. That remains the lowest ACE score for any Atlantic hurricane season since the satellite era began in the 1960s.