The 2023 Hurricane Season in Review: Part 2

Part 2: Eastern Pacific Impacts

The 2023 hurricane season in the North Atlantic and Northeast/Central Pacific Oceans came to a close on November 30 [1]. While activity is technically still possible after this point, the probability of such is fairly low [1]. It’s time to look back at some of the memorable moments of the 2023 hurricane season and what we can take away from the season as a whole. In this blog post, we will focus on the Eastern Pacific basin. Make sure you check out part 1 for an in-depth discussion on the 2023 Atlantic season and its impacts.

The equatorial Pacific Ocean saw a moderate to strong El Niño form by the peak of the summer (Figure 1 and Figure 2) [2, 3]. El Niño conditions are generally associated with above-average tropical cyclone activity in the Eastern and Central Pacific [4]. This is because the warmer upper ocean water in the tropical Pacific during El Niño years supports enhanced shower/thunderstorm activity, which is needed for tropical cyclones to form [5]. Therefore, for the eastern Pacific, most forecasters called for more tropical storms, hurricanes, and major hurricanes than normal as El Niño materialized during the summer of 2023 [6].

Figure 1: SST anomalies from NOAA Coral Reef Watch for the beginning of the 2023 hurricane season, 15 June 2023.

Figure 2: Sea surface temperature anomaly (°C) for August 2023, relative to the 1991-2020 reference period. Data source: ERA5. Credit: Copernicus Climate Change Service/ECMWF.

As we did in part 1 of this blog for the Atlantic basin, we can diagnose tropical cyclone activity in the eastern Pacific using the accumulated cyclone energy index [7]. The accumulated cyclone energy (ACE) of a storm is a metric used to describe the total amount of energy released by a tropical cyclone over its lifetime [7]. ACE is directly related to the sum of the squares of the maximum sustained winds of the tropical cyclone (measured every 6 hours) and the length of time the tropical cyclone existed [7]. Thus, cyclones that are particularly intense and last for longer periods of time will generate the highest ACE values [7]. The cumulative ACE for the 2023 Pacific season was 164, well above the 1991-2020 average of 133.

         Compared to the relative lack of hurricane landfalls in the Atlantic basin, the eastern Pacific witnessed several storms posing direct and significant impacts to land. The first such storm was Hurricane Hilary, which became a large and powerful category 4 hurricane in the tropical Pacific but weakened to a tropical storm before making landfall on Baja California in Mexico and eventually moving over southwestern United States [8]. Hurricane Hilary prompted the issuance of the first ever tropical storm warning for Southern California, according to the National Hurricane Center [8]. Parts of Southern California received nearly a half-year’s worth of rainfall from Hilary [9]. The storm caused roughly $1 billion USD in damage in the western U.S. and Mexico, mainly due to heavy rainfall and flash flooding [10, 16].

Following Hilary, several powerful hurricanes brought catastrophic impacts to mainland Mexico. The month of October was particularly devastating and destructive for the nation. Hurricane Lidia explosively intensified to a Category 4 hurricane before making landfall to the south of Puerto Vallarta in the Mexican state of Jalisco late on October 10 [11]. Hurricane Norma also intensified rapidly into a category 4 hurricane before weakening and making landfall as a Category 1 hurricane with maximum sustained winds of 80 mph near Cabo San Lucas in Baja California, Mexico [12]. The storm’s slow forward motion resulted in copious amounts of rain being dumped across the Baja California peninsula and mainland Mexico [12].

The most notable storm of the Eastern Pacific season in 2023, though, was by far Hurricane Otis. Otis developed out of a tropical wave in the eastern Pacific that tracked slowly to the north and west [13]. Initial forecasts had Otis making landfall near Acapulco, Mexico as a strong tropical storm or a minimal hurricane due to predictions that the storm would experience prohibitive amounts of wind shear that would prevent significant strengthening [13]. Otis defied all expectations, though, when the storm explosively intensified by a whopping 115 miles per hour in wind speed in just 24 hours, a feat only surpassed in the eastern Pacific by Hurricane Patricia in 2015 [13]. This rate of explosive intensification right before landfall left the entire Acapulco metropolitan area off guard, with parts of the city and surrounding areas experiencing winds of over 160 miles per hour [13]. The devastation seen across Acapulco and surrounding areas was simply unprecedented for that area. Two large risk agencies, Moody’s Risk Management Solutions and Verisk, placed the insured losses from Otis in Mexico between 2.5 and 6 billion USD [14]. The true death toll from the hurricane remains unknown, but sources estimate that it could be well over 100 with many people still missing [15].

Figure 4: GOES-18 Infrared satellite imagery of Hurricane Otis as it explosively intensified into a category 5 hurricane before making landfall near Acapulco, Mexico. Satellite loop borrowed from: https://satlib.cira.colostate.edu/event/hurricane-otis/.

Figure 5: Nightime satellite imagery captured from VIIRS showing the city of Acapulco before and after the passage of Hurricane Otis. Satellite loop borrowed from: https://satlib.cira.colostate.edu/event/hurricane-otis/

We have talked about the 2023 hurricane season in the North Atlantic and Northeast Pacific and summarized the activity in both basins as well as some of the most notable storms. Clearly, both basins were active and destructive in their own respects, but the Pacific was notable for producing a storm (Hilary) that brought direct impacts to the southwestern U.S. and for the sheer number of hurricane landfalls in Mexico, including the unexpected intensification and devastating impacts brought on by Hurricane Otis in Acapulco [9, 10, 13]. In our next blog post, we plan to discuss some of the broader patterns, themes, and trends common to both oceanic basins in 2023 and place this in the broader context of overall climate in the 21st century.

References

1.   https://www.nhc.noaa.gov/climo/index.php

2.   https://coralreefwatch.noaa.gov/product/5km/index_5km_ssta.php

3.   https://climate.copernicus.eu/record-high-global-sea-surface-temperatures-continue-august

4.   https://www.climate.gov/news-features/blogs/enso/impacts-el-ni%C3%B1o-and-la-ni%C3%B1a-hurricane-season

5.   https://oceanservice.noaa.gov/facts/how-hurricanes-form.html#:~:text=As%20this%20weather%20system%20moves,cools%2C%20forming%20clouds%20and%20thunderstorms.

6.   https://www.cpc.ncep.noaa.gov/products/Epac_hurr/

7.   https://www.cpc.ncep.noaa.gov/products/outlooks/Background.html

8.   https://www.climate.gov/news-features/event-tracker/former-hurricane-hilary-brought-southern-california-its-first-ever

9.   https://gpm.nasa.gov/applications/weather/news/historic-hurricane-hilary-brings-heavy-rain-and-flooding-us-southwest

10. https://yaleclimateconnections.org/2023/11/the-unusual-2023-atlantic-hurricane-season-ends/#:~:text=Above%2Daverage%20activity%20in%20the,Energy%20(ACE)%20of%20164.

11. https://satlib.cira.colostate.edu/event/tropical-storm-lidia/#:~:text=Lidia%20rapidly%20intensified%20on%20Oct,11%20and%2012.

12. https://apnews.com/article/hurricane-norma-tammy-los-cabo-baja-lesser-antilles-ce64c32ee8c2108fd1d3d7f85ce58054

13. https://www.nesdis.noaa.gov/news/hurricane-otis-causes-catastrophic-damage-acapulco-mexico

14. https://www.insurancejournal.com/news/international/2023/11/15/748359.htm

15. https://www.cbsnews.com/news/hurricane-otis-mexico-dead-missing/

16. https://www.ajg.com/gallagherre/-/media/files/gallagher/gallagherre/natural-catastrophe-report-q3-2023.pdf