In the first half of 2023, the equatorial Pacific flipped from La Niña to El Niño (see WTW’s H1 Natural Catastrophe Review). This transition usually brings environmental conditions favorable for tropical cyclones over large parts of the Pacific Ocean. Consequently, initial forecasts called for above average storminess in the ocean’s three basins: the Eastern North Pacific,[1] the Western North Pacific,[2] and the Central Pacific.[1] However, as the season unfolded, the focus shifted from the number of tropical storms to their strength, with a higher-than-normal proportion of events undergoing rapid intensification. Among the storms that exemplified this phenomenon, Otis in the Eastern North Pacific and Doksuri in the Western North Pacific stood out, both causing considerable societal impacts.
The 2023 Eastern North Pacific hurricane season was slightly above normal in terms of storm counts, with 17 named storms compared with the 1991 – 2020 average of 15. Yet, it was the intensity of these storms that stood out; 10 reached hurricane strength and eight advanced to major hurricanes (Category 3+ on the Saffir-Simpson scale), against historical averages of eight and four respectively. A significant number of these events underwent rapid intensification, contributing to the high count of major hurricanes. Notably, hurricanes Otis and Lidia ranked among the top five most powerful tropical cyclones to make landfall in the Eastern Pacific. Otis was particularly impactful, marking the first Category 5 landfall on record in the basin and causing severe damage in Acapulco, Mexico.
In the Western North Pacific, there were 17 named storms, 12 typhoons and eight major typhoons (equivalent to Category 3+ hurricanes), compared with the 1991 – 2020 average of 25, 16 and nine, respectively. The Western North Pacific mirrored its Eastern counterpart, with several events undergoing rapid intensification during the year. This included Super Typhoon Bolaven in October, which ranked as the second strongest storm of 2023 after Mawar in May (see WTW’s H1 Natural Catastrophe Review). Typhoon Doksuri, which also rapidly intensified became China's costliest tropical cyclone on record, while the remnants of Typhoon Haikui produced unprecedented rainfall in Hong Kong, causing severe flooding. Haikui made landfall only a week after Typhoon Saola, which caused damage in Hong Kong, China and the Philippines.
An average season unfolded in the Central Pacific, with the four tropical cyclones that formed sitting within the normal range of four to five, including Hurricane Dora which contributed to the devastating wildfires in Hawai‘i.
While the Pacific season was not exceptional as a whole, Typhoon Doksuri (known as Egay in the Philippines), which formed in July, broke some notable records. Hailed as the costliest typhoon in China’s history with economic losses of US $15 billion to $20 billion (of which only approximately US $1 billion was insured), it also set 24-hour rainfall records in multiple cities in Fujian province and was the second strongest landfalling Typhoon on record in Fujian after Typhoon Meranti in 2016.
Doksuri was first identified as a tropical depression in the Philippine Sea on July 20 and gradually intensified over two days as it tracked northwest. On July 23, Doksuri suddenly underwent rapid intensification, with sustained windspeeds increasing by over 35 miles per hour in 24 hours. The storm made landfall over the Philippine Babayan Islands at typhoon strength, after which it weakened and continued to track northwest toward China. While over the South China Sea, Doksuri underwent a second period of rapid intensification and made landfall in Fujian province on July 28 with two-minute sustained windspeeds of 110 miles per hour.
The storm left a swathe of destruction, killing 137 people and leaving 285 injured. In Beijing and eastern China, over 60,000 homes collapsed and 95,000 hectares of crops were destroyed, raising questions about the country’s food security in a warmer world.[3]
Three months later, across the Pacific Ocean, a minor tropical disturbance was brewing south of Mexico, initially drawing little attention. Sixteen hours before landfall, the National Hurricane Center predicted that the storm, now named Otis, would hit Acapulco at Category 1 strength (Figure 1). However, this forecast drastically underestimated what was to come. As conditions rapidly deteriorated in the hours approaching landfall, forecasters revised their assessments, describing the unfolding “nightmare scenario” with warnings of life-threatening hurricane winds and flash flooding.
Source: Tomer Burg [@burgwx]. Updated to account for Otis having explosively intensified from a tropical storm to a category 5 hurricane in less than 24 hours. (2023)
Otis strengthened into a Category 5 hurricane in under 24 hours — over three times the defined rate for rapid intensification — with meteorologists labeling this as “explosive intensification”[4] (see “best track” in Figure 1). With updated predictions of a record-breaking Category 5 landfall and less than four hours’ warning, mass evacuation was impractical. Residents were forced to shelter as best they could, facing the most intense winds in the cyclone's front-right quadrant.
Acapulco is best known for its glamorous beach resorts, and the bulk of the insured loss — estimated to reach $4 billion to $6 billion — is expected to stem from holiday accommodation and luxury homes (Figure 2).
Source: Xinhua / Alamy
Alongside the holiday opulence, Acapulco also contends with extreme poverty and low insurance penetration rates, so a significant proportion of the estimated US $20 billion economic loss — particularly from many of the 220,000 homes that were damaged — is likely to be uninsured and borne by the government or the homeowners themselves.
In recent years, models have greatly advanced in predicting the intensity of tropical cyclones when they strengthen at a normal or slow pace. However, accurately predicting rapid intensification, especially in storms like Doksuri that experience multiple rapid intensification episodes, remains a major challenge.[5] This forecasting difficulty has serious implications for preparedness and emergency response, as seen with Otis, where many were caught off guard due to inadequate warnings of the looming danger.
The difficulty in forecasting rapid intensification stems in part from our limited understanding of the complex atmospheric and oceanic interactions that occur during these events.
This challenge is compounded by limitations in observational data, especially in the middle of oceans where such data are often scarce, and the need for resource-intensive high-resolution modeling to adequately simulate the physics of rapid intensification.
However, progress is being made. The Hurricane Analysis and Forecast System (HAFS), implemented by the National Hurricane Center (NHC) in 2023, aims to address some of these challenges. HAFS integrates advanced data assimilation techniques, high-resolution physics and improved modeling of the atmosphere-ocean interface, offering the potential for better rapid intensification predictions.
NHC forecasters hope this will allow them to forecast at least 50% of rapid intensification episodes, an increase on the 30% hit rate of current models.[6]
The double rapid intensification of Doksuri and the “explosive” rapid intensification of Otis occurred in a busy year for the phenomenon. A key question arising from the events of 2023 is whether there is an emerging trend of more cyclones experiencing rapid intensification. Studies suggest that the number of tropical cyclones undergoing rapid intensification is rising[7] and the intensification rate itself is increasing, particularly for the more extreme episodes.[8]
In Hurricane Otis' case, what made the rapid intensification so devastating was the proximity of the storm to the coastline and its imminent landfall. Although it surprised forecasters, it is not an isolated occurrence. Recent research shows that offshore areas within 400 kilometers of the coastline have experienced a significant increase in the number of rapid intensification events, tripling from 1980 to 2020.[9]
While it is now generally acknowledged that tropical cyclone rapid intensification is on the up, the question that naturally follows is, why? Although research in this area is still growing, evidence increasingly points toward a significant contribution from human-induced climate change.[10] With global temperatures set to rise further over the coming decades, we will likely see more seasons like 2023, marked by a high proportion of storms that rapidly intensify. Enhanced forecasting techniques, such as HAFS, and more robust disaster preparedness strategies are urgently needed to mitigate the impacts of such unpredictable and devastating storms.
