On October 1, a broad area of low pressure formed over the southwestern Caribbean Sea, absorbing the remnants of Tropical Storm Kirk by the next day. Early on October 2, the National Hurricane Center (NHC) began monitoring the system for tropical development. On the same day, the disturbance experienced a burst of convection, possibly associated with a tropical wave moving into the region, which led to a small surface low forming to the southwest of Jamaica on October 3. While strong upper-level winds initially inhibited development, the disturbance gradually became better organized as it drifted generally northward and then westward toward the Yucatán Peninsula. By October 6, the disturbance had developed well-organized deep convection, although it still lacked a well-defined circulation. The storm was also posing an immediate land threat to the Yucatán Peninsula and Cuba. Thus, the NHC initiated advisories on Potential Tropical Cyclone Fourteen at 21:00 UTC that day. By the morning of October 7, radar data from Belize found a closed center of circulation, while satellite estimates indicated a sufficiently organized convective pattern to classify the system as a tropical depression. The newly-formed tropical cyclone then quickly strengthened into Tropical Storm Michael at 12:00 UTC that day. The nascent system meandered before the center of circulation relocated closer to the center of deep convection, as reported by reconnaissance aircraft that was investigating the storm. Despite moderate vertical wind shear, Michael proceeded to strengthen quickly, becoming a high-end tropical storm early on October 8, as the storm's cloud pattern became better organized. Continued intensification occurred, and Michael attained hurricane status later on the same day.
Shortly afterwards, rapid intensification ensued and very deep bursts of convection were noted within the eyewall of the growing hurricane, as it passed through the Yucatán Channel into the Gulf of Mexico late on October 8, clipping the western end of Cuba at Category 2 intensity. Meanwhile, a 35-nautical-mile-wide (65 km) eye was noted to be forming. The intensification process accelerated on October 9, with Michael becoming a major hurricane at 18:00 UTC that day. Rapid intensification continued throughout the day as a well-defined eye appeared, culminating with Michael achieving its peak intensity at 17:30 UTC that day as a Category 5 hurricane, with maximum sustained winds of 160 mph (260 km/h) and a minimum central pressure of 919 millibars (27.1 inHg). In just under 24 hours, its central pressure had fallen by 42 mbar (1.2 inHg). Simultaneously, Michael made landfall on the Gulf Coast of the United States near Mexico Beach, Florida, ranking by pressure as the third-most intense Atlantic hurricane to ever make landfall in the United States, and making it the first Category 5 hurricane to strike the contiguous United States since Hurricane Andrew in 1992. The storm was originally considered a high-end Category 4 hurricane, but post-season reanalysis (which the NHC routinely performs for every tropical cyclone in their area of responsibility) concluded that it was indeed a Category 5 hurricane at this point.
Michael maintained Category 5 intensity for less than one hour; once inland, Michael began to rapidly weaken, as it moved over the inner Southeastern United States, with the eye dissipating from satellite view, weakening to a tropical storm roughly twelve hours after it made landfall. Moving into the Carolinas early on October 11, the inner core of the storm collapsed as the storm's rainbands became prominent to the north of the center. Later that day, Michael began to show signs of becoming an , as it accelerated east-northeastward toward the Mid-Atlantic coastline, with cooler air beginning to wrap into the elongating circulation, due to an encroaching frontal zone; it became extratropical at 00:00 UTC October 12. Afterward, Michael began to restrengthen while moving off the coast, due to baroclinic forcing. Michael subsequently accelerated towards the east, strengthening into a powerful extratropical cyclone by October 14. On October 15, Michael's extratropical remnant approached the Iberian Peninsula and turned sharply towards the southeast, making landfall on Portugal early on October 16. Soon afterward, Michael's extratropical remnant absorbed the remnants of Hurricane Leslie to the east, following a brief Fujiwhara interaction. Afterward, Michael's remnant quickly weakened, dissipating over Spain later on the same day.