Early on October 2, the National Hurricane Center (NHC) began monitoring a broad area of low pressure that had developed over the southwestern Caribbean Sea. While strong upper-level winds initially inhibited development, the disturbance gradually became better organized as it drifted generally northward and then eastward 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 16:55 UTC that day. The nascent system meandered before the center 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 began to ensue 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. Meanwhile, a 35 nmi (65 km) wide eye was noted to be forming. The intensification process accelerated on October 9, with Michael becoming a major hurricane at 21:00 UTC that day. In addition, the central pressure in the eye was noted to have dropped about 20 mb (0.59 inHg) in the span of 6 hours, into the first hours of October 10. Rapid intensification continued throughout the day as a well-defined eye appeared, culminating with Michael achieving its peak intensity at 18:00 UTC that day as a high-end Category 4 hurricane, with maximum sustained winds of 155 mph (250 km/h) and a minimum central pressure of 919 mbar (27.14 inHg), just below Category 5 intensity, as it 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. It is possible, however, that Michael may have reached Category 5 intensity as it made landfall, based on ongoing analysis from several citizen meteorological agencies and the National Hurricane Center (NHC).
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. However, Michael managed to reach Georgia as a Category 3 hurricane, becoming the first major hurricane to enter the state since 1898. 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. Afterward, during the early hours of October 12, Michael began to restrengthen while moving off the coast, due to baroclinic forcing. Shortly afterward, Michael completed its extratropical transition around 09:00 UTC on the same day, as the storm became fully embedded within the frontal zone. 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. Following landfall, Michael's remnant quickly weakened, dissipating later on the same day.