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Hurricane Otis became the strongest hurricane ever recorded at landfall in the Eastern North Pacific Basin. The region of Acapulco, Mexico, a harbour with over 1 million inhabitants was not prepared for the winds of Otis that reached gust speeds of over 329kmh−1 by an in situ sensor. This study describes the rapid intensification and landfall of Otis using a blend of satellite imagery, reanalysis and station data. Tropical Storm Otis formed on 22 October 2023 several hundred kilometres off the western coast of Mexico. Only 72h later, Otis made landfall as the strongest hurricane ever recorded at the Mexican Pacific coast. The eyewall of Hurricane Otis crossed directly through the harbour of Acapulco and the impact took the lives of at least 51 people, according to official sources (Associated Press, 2023). The Mexican government as well as insurance and catastrophe risk companies have reported that Otis caused damages estimated between 3.5 and 15 billion US dollars making it the costliest hurricane in Mexican history (Gallager, 2023; Merida, 2023; Moody, 2023). After its genesis, official intensity forecasts on 23 October by the National Hurricane Center (NHC) suggested that Otis would remain a Tropical Storm (Figure 1a) and public advisories did not suggest it would become a strong hurricane (NHC, 2023). However, on 24 October satellite imagery (such as Figure 1b) showed a clear eye and a prominent eyewall and flight reconnaissance measured wind speeds of a Category 3 hurricane. Hurricane Otis intensified unexpectedly only 12h before making landfall, as the maximum sustained wind speeds increased in this period by nearly 125kmh−1 (67 kts). On 25 October 2023 at around 12:30 local time (0630 utc), it made landfall as the strongest hurricane ever recorded at the Mexican Pacific coast (Figures 1c and d). Figure 2 shows the track of Hurricane Otis and the average environmental fields for 22/23 October, when it was still a Tropical Storm. The sea-surface temperature (SST) field shows that Otis would later pass over a pool of warm waters a few kilometres south of Acapulco. The SST in this region exceeded 30.5°C which was +1.2degC warmer than climatology for these dates. These warm SST anomalies along Otis' track likely played an important role in its intensification and were partially due to the positive phase of the El Niño-Southern Oscillation event of 2023 (Climate Change Service, 2023). The trough observed in northern Mexico (Figure 2) may have played a role in the track and intensification of Otis. For instance, the environmental wind shear (850–200hPa) within 500km of Acapulco 1–2 days prior to the landfall of Otis was 15ms−1 according to ERA5 data, which is considered a strong value (Rios-Berrios et al., 2023). Further research is required to understand the intensification of Otis and the roles of the vertical wind shear and SSTs. The probability distribution of the intensification rates (kt 24h−1) in the Eastern Pacific (EP) Basin since 1979, using data from the International Best Track Archive (IBTrACS, Knapp et al., 2018), illustrates how extreme the intensification of Hurricane Otis was (Figure 3). Rapid intensification (RI) is defined by an intensification rate higher than the threshold of +30 knots in a 24h period. Figure 3 shows that RI is a rare occurrence (5% of cases). Hurricanes Patricia (2015) and Otis (2023) underwent the first and second most extreme RI processes in the EP basin, respectively. One key difference is that Hurricane Patricia weakened rapidly several hours before landfall (Rogers et al., 2017) whereas Hurricane Otis reached its life-time maximum intensity only a few dozen kilometres off the coast. The strengthening of Otis just prior to landfall led to a worst-case scenario. IBTrACS data show how the maximum sustained wind speed peaked right at the time of landfall (Figure 4a). The Mexican National Sea Level Monitoring Service has a station located in the Port System Administration facilities of Acapulco (Acapulco ASIPONA), equipped with meteorological and sea level sensors. At this station, during the landfall of Hurricane Otis, wind gusts of 329kmh−1 (178kn) were recorded (Figure 4b), which are considered amongst the top 10 strongest wind gusts ever recorded on Earth with digital anemometers (Masters, 2023; WMO, 2023). The maximum sustained wind speeds at landfall were 182kmh−1 (98kn) when a minimum pressure of 963hPa was recorded, having fallen from 1008hPa just 6h earlier (Figure 4c). Precipitation from the Multi-Source Weighted-Ensemble Precipitation (MSWEP) v2 dataset (Beck et al., 2019) shows that precipitation rates within 500km of the storm were relatively low for a TC in this intensity range (García-Franco et al., 2023). The average precipitation within 100km of the storm increased notably as the storm intensified and approached land (Figure 4d). The population of Acapulco was warned of the landfall of Hurricane Otis as a Category 5 storm <6h prior to landfall due to its unexpected RI. RI remains difficult to forecast in numerical weather prediction models (DeMaria et al., 2021) due to gaps in our observations and the insufficient spatial resolution of mesoscale numerical weather prediction models (DeMaria et al., 2021; Rogers, 2021). Evidence suggests that climate change is making RI more frequent and tropical cyclones are expected to produce more rainfall (Emanuel, 2017; Knutson et al., 2020). Even though climate change does not cause a single hurricane to undergo RI, the environment that favours RI is made more likely by climate change through increases in SSTs and potential intensity (Bhatia et al., 2022). The landfall of Otis caused severe infrastructure damage, loss of life and left over one million people without access to food, water and power and cut off telecommunications and roads for weeks. Local vulnerabilities, such as infrastructure that is not designed to withstand these types of events, and the lack of preparation in the local decision-makers and in the population, exacerbate the impacts of hydrometeorological events such as Otis (Dominguez et al., 2021). Future strategic planning must include measures that build resilience to Otis-like events and early warning systems that consider a multi-hazard approach as a first step to reducing disaster risk (Bowman et al., 2014). Jorge L. García-Franco: Conceptualization; data curation; formal analysis; investigation; methodology; project administration; resources; software; validation; visualization and writing—original draft. Octavio Gómez-Ramos: Data curation; investigation; supervision; validation; writing—original draft and methodology. Christian Dominguez: Data curation; formal analysis; investigation; methodology; visualization and writing—original draft. To the work group of the National Sea Level Monitoring Service (Servicio Mareográfico Nacional) for the generation and recovery of wind speed, gust speed and atmospheric pressure data: www.mareografico.unam.mx. All the datasets used in this study are publicly available. ERA5 reanalysis data are available from the Copernicus Climate Change Service Climate Data Store at https://doi.org/10.24381/cds.bd0915c6 (Hersbach et al., 2020). The IBTrACS dataset is publicly available (Knapp et al., 2018) at https://www.ncei.noaa.gov/products/international-best-track-archive. The GPM dataset is available at https://gpm.nasa.gov/data/ (doi:10.5067/GPM/GMI/BASE/07). MSWEP (Beck et al., 2019) is available for download via Google Drive after applying at www.gloh2o.org/mswep/.
García-Franco et al. (Wed,) studied this question.