Jeff Masters Weather Blog

The unusual 2023 Atlantic hurricane season ends » Yale Climate Connections


As the 2023 Atlantic hurricane season began, hurricane experts were unsure what to expect: How many named storms would form? How many major hurricanes?

On one hand, scientists were forecasting an El Niño. The natural phenomenon is part of a recurring ocean-and-atmosphere pattern that warms and cools the eastern tropical Pacific through El Niño and La Niña events that last from one to three years. El Niño conditions usually lead to below-average hurricane seasons because of an increase in wind shear, which can disrupt the structure of tropical cyclones.

On the other hand, the oceans were already record-warm. And warm sea surface temperatures tend to lead to above-average hurricane activity.

The seasonal forecast team at Colorado State University wasn’t sure which phenomenon would prove more important.

“There are no great analogs for the current and projected situation of a moderate to strong El Niño combined with a record warm Atlantic,” the team wrote in its August 3, 2023, forecast.

Now we have an answer: The record-warm sea surface temperatures won out, helping the 2023 Atlantic hurricane season finish well above average for storm quantity and accumulated energy, and near average for hurricanes.

There were 20 named storms, seven hurricanes, three major hurricanes, and an Accumulated Cyclone Energy (ACE) of 146. In comparison, the long-term averages for the period 1991-2020 were 14.4 named storms, 7.2 hurricanes, 3.2 major hurricanes, and an ACE of 123. The 20 named storms tied 2023 with 1933 as the fourth-most on record, behind only 2020 (30 named storms), 2005 (28), and 2021 (21).

Figure 1. Departure of vertical wind shear from average, August to October 2023. The black box denotes the Atlantic main development region (MDR) for hurricanes, defined to be 10–20°N, 85– 50°W. Wind shear was unusually far below average, particularly considering that this was an El Niño year. (Image credit: Colorado State University)
Figure 2. Observed tropical cyclone tracks for the 2023 Atlantic hurricane season. (Image credit: NHC)

Wind shear over the tropical Atlantic in 2023 was much lower than usual for an El Niño year (Figure 1). Fortunately, the steering pattern in 2023 was typical of that for an El Niño year, with a weaker and farther-east Bermuda-Azores High leading to most storms recurving out to sea without affecting land (Figure 2).

Did global warming play a role in the 2023 Atlantic hurricane season?

The record-warm waters in the Atlantic in 2023 resulted in part from a slow increase in Atlantic sea surface temperatures of about 1 degree Celsius over the past century, plus an unusual atmospheric circulation pattern brought on by the rapid transition from the strong La Niña events in 2022–2022 to strong El Niño conditions during 2023. While the El Niño/La Niña cycle is natural, there has been research published linking the unusual circulation patterns of 2023 to human-caused climate change: For example, a 2023 study in ScienceAdvances found that smoke from the record 2019-2020 Australian wildfire season made an “important contribution” to the 2020-2022 strong La Niña events. And a 2023 Nature Communications study found that persistent high pressure over Greenland — which brought unusual circulation patterns that led to record warming to the North Atlantic in 2023 — has been made more likely because of lower spring snow cover as a result of global warming. Canada had unusually low snow cover during the spring of 2023.

a chart showing a gradual rise in sea surface temperatures in the Atlantic Main Development Region between 1910 and 2023.
Figure 3. Departure of sea surface temperature from average in August to October for 1910-2023. Sea surface temperatures have been increasing by 1.05 degree Celsius per century, but 2023 had an extraordinarily high departure from average. (Image credit: NOAA)

Two landfalling hurricanes and 3 landfalling tropical storms

Only one major Atlantic hurricane made landfall in 2023: Hurricane Idalia, which struck Florida’s Big Bend region on August 27 as a Category 3 storm with 125 mph winds. There was one other hurricane landfall in 2023: Hurricane Tammy, which hit Barbuda (population 1,600) in the Leeward Islands on October 22 as a Category 1 storm with 85 mph winds.

Three tropical storms made landfall: Harold in South Texas on August 22 with 50 mph winds; Franklin in the Dominican Republic on August 23 with 50 mph winds; and Ophelia in North Carolina on September 23 with 70 mph winds. In addition, the only Category 5 hurricane of 2023, Lee, made landfall in Nova Scotia on September 16 as a post-tropical cyclone with 60 mph winds.

A remarkably low death toll and damage tally from the 2023 Atlantic hurricane season

The 2023 Atlantic hurricane season had a remarkably low death toll. Unofficially, three storms caused a total loss of life of 12:

This year is the first Atlantic season since 2016 without at least two billion-dollar U.S. landfalls. According to Gallagher Re, the 2023 total damage from Atlantic named storms was about $4 billion — the lowest since 2015. Three storms caused over $100 million in damage:

  • Idalia: $2.4 billion
  • Lee: $150 million
  • Ophelia: $375 million

In addition, an Eastern Pacific storm, Hurricane Hilary, did $1 billion in damage in the western U.S. and northwestern Mexico.

The damage from Idalia in Florida was relatively modest when you consider that the hurricane plowed ashore as a high-end Category 3 storm with 125 mph winds. Fortunately, that landfall came near low tide on Florida’s sparsely populated Big Bend, with a relatively confined zone of hurricane-force winds. The last time a major U.S. landfall wreaked so little financial havoc was in 1999, when Hurricane Bret smashed into Texas’s Padre Island, midway between Brownsville and Corpus Christi, at Category 3 strength. Much like Idalia, Bret was a relatively compact storm that struck a sparsely populated stretch of coastline. Bret’s damage was limited to $127 million (2023 USD), and just one life was lost.

The deadliest Atlantic storms of 2023 were unnamed

The two deadliest Atlantic storms of the 2023 hurricane season both affected Hispaniola, killing 51 and 26 people, respectively, but neither were named storms.

On June 2-3, a tropical disturbance that had formed in the southwestern Caribbean moved to the northeast over Hispaniola, dumping heavy rains on Haiti. According to reliefweb, the resulting flooding killed 51 people, left 18 others missing, and made over 13,000 people homeless.

On November 17-18, a tropical disturbance in the southwest Caribbean, designated Potential Tropical Cyclone 22, brought torrential rains to Haiti, the Dominican Republic, Jamaica, and eastern Cuba, as it moved to the northwest across the central Caribbean and then into the Turks and Caicos Islands. The central Dominican Republic had especially devastating flooding, which killed 24 people and led to extensive property and infrastructure damage in the tens of millions. According to Oficina Nacional de Meteorologia (ONAMET), much of the central Dominican Republic saw widespread rainfall totals of 150-300 mm (six to 12 inches) in the two separate 24-hour periods of November 17 and 18. The highest 24-hour rainfall total was 431 mm (16.97 inches) at Arroyo Hondo Viejo near Santo Domingo. Several other stations exceeded 400 mm (15.7 inches) of rain in a four-day period between November 16 and 19. Two deaths in neighboring Haiti also occurred from the storm.

The Colorado State forecast team put together a selection of some of the notable statistics from the 2023 season:

  • 20 named storms formed in the Atlantic this season. That is tied with 1933 for the fourth most on record, trailing 2020 (30 named storms), 2005 (28 named storms), and 2021 (21 named storms).
  • 146 ACE was generated during 2023, making the 2023 Atlantic hurricane season an above-normal season by NOAA’s definition. The Atlantic has not had a below-average season per NOAA’s definition since 2015.
  • 13 named storms formed in the Atlantic from August 20th through September 28. That is the most on record between August 20 and September 28, breaking the old record of 12 named storm formations set in 2020.
  • Five hurricanes formed in the Atlantic between August 26 and September 18. This ties the record for most hurricane formations between August 26 and September 18, first set in 1955 and occurring in 2004 and 2012.
  • Tropical Storms Bret and Cindy formed in the tropical Atlantic (south of 23.5°N, east of 60°W) in June. This is the first time on record that two named storms formed in the tropical Atlantic in June on record.
  • Hurricanes Franklin and Idalia had max winds of 110 mph simultaneously – the first time that this occurred during August since 1950.
  • Hurricane Franklin’s central pressure reached a lifetime maximum low of 926 hPa – the lowest central pressure for a hurricane that far north (29°N) in the open Atlantic on record.
  • Hurricane Idalia made landfall with max winds of 125 mph – the strongest hurricane to make landfall in the Big Bend region of Florida since 1896.
  • Hurricane Lee intensified by 70 knots (80 mph) in 24 hours. Six other Atlantic hurricanes in the satellite era (since 1966) have intensified by 70 knots (80 mph) in 24 hours: Wilma (2005), Felix (2007), Ike (2008), Matthew (2016), Maria (2017) and Eta (2020).
  • Tropical Storm Philippe was a named storm for 12.75 days but only reached a maximum intensity of 50 mph. All other storms in the Atlantic lasting that long had a maximum intensity of at least 70 mph.
  • Tropical Storm Sean formed at 33.1°W on October 10th – the farthest east that a named storm has formed in the tropical Atlantic (south of 23.5°N) this late in the calendar year on record.
  • Tammy became a hurricane on October 20 — the latest hurricane on record in the tropical Atlantic (south of 20°N, east of 60°W) for any calendar year.

Above-average activity in the Eastern Pacific

The 2023 Eastern Pacific hurricane season was also above average in activity, with 17 named storms, 10 hurricanes, eight major hurricanes, and an Accumulated Cyclone Energy (ACE) of 164. In comparison, the long-term averages for the period 1991-2020 were 16.6 named storms, 8.8 hurricanes, 4.6 major hurricanes, and an ACE of 133. Two of the top-five strongest Eastern Pacific hurricanes on record to make landfall occurred in 2023: Otis (No. 1 with 165 mph winds) and Lidia (tied for No. 5 with 140 mph winds). Both hit Mexico, but Otis was by far the most destructive of the two, ravaging the city of Acapulco (see Tweet above, blaming much of the damage there on the decision to engineer Acapulco’s buildings for earthquakes, but not major hurricanes). Otis caused at least 50 deaths (perhaps many more) and damage exceeding $10 billion, potentially making it the costliest hurricane in Mexico’s history. Among the factors that made Otis such a catastrophe was its unexpectedly rapid strengthening from tropical storm to landfalling Category 5 storm in less than 24 hours, and its landfall in the immediate Acapulco area, where hurricanes typically graze the coast rather than moving bodily inland.

Read: Acapulco, a month after Hurricane Otis

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