Hurricane Otis

Hurricane Otis was a compact but very powerful tropical cyclone which made a devastating landfall near Acapulco as a Category 5 hurricane in October 2023. Otis was the first Pacific hurricane on record to make landfall at Category 5 intensity and became the strongest Pacific hurricane to make landfall, surpassing Hurricane Patricia of 2015. The resulting damage made Otis the costliest tropical cyclone to strike Mexico on record, surpassing Hurricane Wilma of 2005. The fifteenth tropical storm, tenth hurricane, eighth major hurricane, and second Category 5 hurricane of the 2023 Pacific hurricane season, Otis originated from a disturbance several hundred miles south of the Gulf of Tehuantepec. Initially forecast to stay offshore and to only be a weak tropical storm at peak intensity, Otis instead underwent explosive intensification to reach peak winds of 165 mph (270 km/h) and weakened only slightly before making landfall as a powerful Category 5 hurricane. Once inland, the hurricane quickly weakened before dissipating the following day.

Making landfall just west of Acapulco, Otis's powerful winds severely damaged many of the buildings in the city. Landslides and flooding resulted from heavy rain. Communication was heavily cut off, initially leaving information about the hurricane's impact largely unknown. In the aftermath, the city had no drinking water and many residents also lost power. The government of Guerrero mobilized thousands of military members to aid survivors and assist in recovery efforts. Thousands of recovery items were sent out to those affected and donations were sent out to each of the affected families.

The hurricane caused at least 52 deaths and left 32 others missing. Total damage from Otis was estimated to be billions of dollars (2023 USD), with several agencies estimating $12–16 billion in damage, making it the costliest Pacific hurricane on record, surpassing Hurricane Manuel in 2013.

On October 15, 2023, the National Hurricane Center (NHC) noted that an area of low pressure was expected to form several hundred miles south of southeastern Mexico over the next seven days. This forecast came to fruition on October 18 with the development of a broad low several hundred miles south of the Gulf of Tehuantepec. Accompanied by disorganized convection, organization into a tropical cyclone was deemed likely within five days as the system meandered in the same general area. Convection grew in scope the following day, though upper-level wind shear displaced this to the west of the system's center. Throughout October 21, convection increased in coverage and the system's surface circulation became more defined. The disturbance's meandering motion shifted to a northward crawl as it was wedged between a ridge to the northeast and a trough to the northwest. Following further convective organization, the system became Tropical Depression Eighteen-E at 12:00 UTC (07:00 a.m. CDT) on October 22. At this time, the depression was situated roughly 535 mi (860 km) south-southeast of Acapulco, Mexico. Six hours later, the system intensified into a tropical storm, at which time it was assigned the name Otis.

Light to moderate southeasterly wind shear displaced convection northwest of Otis's surface circulation during the overnight hours of October 22–23. The lack of vertical alignment and dry mid-level air delayed potential intensification despite an otherwise favorable environment consisting of high sea surface temperatures and abundant atmospheric moisture. Sea surface temperatures ahead of the system averaged 86–88 °F (30–31 °C), above average for this time of year. The high temperatures resulted from a combination of a record-warm September for Mexico, an ongoing El Niño, and the influence of global warming. The system's motion shifted from due north to north-northwest during this time, remaining around 4–5 mph (6–8 km/h). A convective band developed halfway around the storm by the afternoon of October 23, and the surface circulation and thunderstorm activity moved closer together. During the overnight of October 23–24, the storm moved into a region of more favorable conditions, with higher sea surface temperatures and weaker vertical wind shear. Microwave satellite imagery depicted a low-level ring structure, often a precursor to rapid intensification, despite the overall sheared appearance of the system. The storm's forward motion also increased during this time, potentially offsetting the negative impacts of southeasterly wind shear. As a result, upper-level outflow expanded noticeably and the system's core became centered in the convection. This led to Otis beginning an explosive intensification phase that would continue until just before landfall. As the morning of October 24 progressed, outflow continued to expand in all directions atop Otis and many banding features circulated the storm. The improvement in outflow was accentuated by a powerful jet streak—a wind maxima within the jet stream—which accelerated the rate of latent heat dispersal and fostered convective development. Otis commenced explosive intensification and became a hurricane by 12:00 UTC (07:00 a.m. CDT) on October 24.

Shortly after 18:00 UTC (1:00 p.m. CDT), the only Air Force Reserve Unit Hurricane Hunter mission flown into Otis penetrated its eye, and the observations indicated that Otis had already reached Category 3 intensity and thus become a major hurricane. This was substantially above estimates using the Dvorak technique, which ranged from only 70 mph (110 km/h) to 105 mph (165 km/h); Otis was persistently stronger than indicated by the Dvorak technique throughout the rapid intensification phase. Operationally, the NHC had only upgraded Otis to a Category 1 hurricane on the Saffir-Simpson scale. Explosive intensification continued throughout the day into the nighttime hours, in what was described as a "nightmare scenario" by Eric Blake at the NHC. A prominent pinhole eye developed as the night progressed, surrounded by intense convection reaching −103 to −112 °F (−75 to −80 °C). Otis reached its peak intensity as a Category 5 hurricane with maximum sustained winds of 165 mph (270 km/h) and a minimum central pressure of 922 mb (27.23 inHg) at 03:00 UTC on October 25 (10:00 p.m. CDT, October 24)–just nine hours after attaining Category 3 intensity–while located just 60 mi (95 km) south-southeast of Acapulco. Immense lightning activity occurred throughout the intensification phase, approximately 26,000 strikes in 24 hours, with the greatest activity taking place in the 55 minutes leading up to landfall. As Otis neared landfall, satellite images showed some cooling and filling in of the eye, suggesting that the storm weakened slightly before landfall. By 05:45 UTC (12:45 a.m. CDT), Isla de La Roqueta [es] entered the hurricane's eyewall and the storm's core made landfall just west of Acapulco around 06:45 UTC (1:45 a.m. CDT) just below peak intensity, though still at Category 5 intensity, with winds of 160 mph (260 km/h) and a minimum central pressure of 929 mb (27.43 inHg). Once onshore, the hurricane rapidly weakened as it interacted with the mountains of the Sierra Madre del Sur. Within two hours, its eye disappeared from satellite imagery and lightning activity ceased. Utilizing statistical inland decay models, the NHC estimated Otis to have fallen below hurricane status by 18:00 UTC (1:00 p.m. CDT). The storm's surface circulation dissipated shortly thereafter, marking the cessation of Otis's time as a tropical cyclone.

The rapid intensification of Otis was among the most poorly forecast in the modern era. Meteorologists Jeff Masters and Bob Henson at Yale University called the underestimation "one of the biggest and most consequential forecast-model misses of recent years". Numerical weather prediction models failed to capture the magnitude of explosive intensification that occurred, in part due to a dearth of data. Several experts, including director of the National Hurricane Center Michael Brennan, noted that there are very few instruments — such as ocean buoys or radar — available for evaluating hurricane strength in the East Pacific, leaving forecasters reliant on satellite data. As described by the New York Times, forecasts of Otis upon its formation on October 22 "didn’t show much to be concerned about". In their first advisory, the NHC forecast a peak intensity of just 45 mph (75 km/h), 120 mph (195 km/h) lower than its actual peak intensity, with the system moving north-northwest and later west away from the Mexican coastline. Forecasters John Cangialosi and Lisa Bucci noted that many models showed the storm outright dissipating within five days.

Early on October 23, Blake noted that models were incorrectly diagnosing conditions and showing Otis intertwined with the Intertropical Convergence Zone. He adjusted his forecast to show a faster motion which would bring the system onto the Mexican coastline on October 26. Later that day, forecasters Cangialosi and Sandy Delgado noted a substantial disparity in various model solutions, with results differing based on how vertically aligned the storm would become or not become. Conditions for a more potent system became more apparent during the overnight hours of October 23–24. This included high sea surface temperatures, lower wind shear, and abundant moisture. The system also became vertically aligned. The Statistical Hurricane Intensity Prediction Scheme (SHIPS) rapid intensification index increased to 25 percent, leading forecasters to raise their intensity predictions above most model outputs. At 09:00 UTC (4:00 a.m. CDT) on October 24, less than 24 hours before landfall, the NHC expected Otis to intensify into a Category 1 hurricane as it moved ashore. Sixteen hours prior to landfall, the system was forecast to move ashore at least five hours later than it actually did. The dramatic rate of intensification was not apparent until reconnaissance aircraft sampled the storm during the afternoon of October 24. At 00:00 UTC on October 25 (7:00 p.m. CDT, October 24), just under six and a half hours before the storm made landfall, the NHC upgraded Otis to a Category 4 hurricane and explicitly forecast it to become a Category 5 hurricane before making landfall.