A tropical wave moved over the Atlantic around the middle of September. It took a quite southerly track and had little in the way of organized thunderstorm activity before reaching the Caribbean on September 21. Though Caribbean waters were warm, strong upper-level winds from the outflow of the enormous Hurricane Fiona hindered the system from consolidating. Despite this, a well-defined surface low formed on the 22nd. At first, there wasn't enough convection near it to classify as a tropical cyclone, but it became Tropical Depression Nine early on September 23. Only late that day when Fiona was approaching Canada did the associated upper-level winds finally die down enough for the depression to strengthen more easily. It was named Tropical Storm Ian that night. The "I" name was assigned to this storm because in between being named a tropical depression and a tropical storm, a new depression (Ten) formed and took the name Hermine.
Wind shear had diminished, but Ian had internal structural issues to overcome. The low- and mid-level circulations were not vertically stacked, preventing organization for a day or so. Meanwhile, the storm moved westward, passing well south of Jamaica. After the vortices had become better aligned on September 25, the system still had trouble developing deep convection due to dry air inside in the circulation. Ultimately, the favorable conditions of the western Caribbean allowed Ian to overcome this obstacle as well and begin rapid intensification.
This trend brought the storm to hurricane strength by early on September 26 as it gradually curved toward the north. Ian managed to reach category 2 by that night without having a complete eyewall; rather, the core still consisted of spiral bands. Another burst of intensification occurred just before landfall in western Cuba overnight. At landfall, it had maximum winds of 125 mph (category 3 intensity) and a minimum central pressure of 947 mb. The storm's passage northward over land did weaken it, but the inner structure actually improved, if anything. When the center emerged over the Gulf of Mexico during the morning of the 27th, it almost immediately cleared out a large eye. By this time, Ian was feeling the influence of a potent trough of low pressure over the eastern United States and turned very gradually east of north in its southwesterly flow.
The hurricane underwent an eyewall replacement cycle that afternoon. In this process, a secondary eyewall forms outside the first, ultimately contracting and replacing it. Ian's maximum strength did not increase during this process, but its radius of tropical storm and hurricane-force winds increased. A new, larger eye began to emerge that evening. Soon, the hurricane was intensifying again and became a category 4. This trend unforunately continued almost until landfall. Ian ultimately reached a peak strength as a category 5 hurricane with 160 mph winds and a central pressure of 937 mb during the morning of September 28. (Note: Ian was upgraded to a category 5 in post-season analysis; operationally, it was considered a 155 mph category 4 at the time of peak intensity.) A few hours later, the storm made landfall along the western coast of Florida at only the slightly reduced intensity of 150 mph winds and a pressure of 940 mb.
The imapcts to the landfall region were devastating; the slow-moving storm brought significant storm surge just south of the landfall point and extreme rainfall totals generally north of the center. Ian moved northeast across the state for the next day or so and weakened down to a tropical storm before emerging into the Atlantic ocean early on the 29th. By that time, the cyclone was no longer fully tropical; its interaction with a trough had lent it some frontal features. The windfield was large and less concentrated at the center, and similarly for rainfall. Nevertheless, access to the energy of the Gulf stream did help Ian to regain some strength and it became a hurricane again later that day.
Ian made its final landfall in South Carolina during the afternoon of September 30 as a category 1 hurricane with peak winds of 85 mph and a central pressure of 977 mb. Shortly after landfall, the storm lost what remained of its warm core and transitioned to a post-tropical system. The remnants weakened rapidly and merged with another disturbance over the mid-Atlantic the next day. The moisture from Ian contributed to a prolonged rain event for the coastal northeastern United States over the following several days.
The above image shows Ian at peak intensity a few hours before landfall in Florida.
During the latter part of Ian's track, it consistently deviated to the east of most forecasts due to the difficulty of predicting its interaction with a trough over the eastern United States.
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