Alberto: A Rare Breed of Inland Tropical Cyclone Over the Midwest

Tropical Depression Alberto greeted the Midwest with breezy and rainy conditions as it moved from Tennessee into Michigan Wednesday into Thursday, but the storm gained the gaze of meteorologists as it began to appear better organized more than 700 miles from its landfall location. 

Robust curved bands showed up on radar imagery surrounding a clear and concise center of circulation. This slight reorganization is likely due to daytime heating and abundant moisture in the Midwest. 

Alberto transitioned to a post-tropical cyclone about 20 miles west-southwest of Alpena, Michigan Thursday morning.

But how did it get that far? 

Under the right atmospheric and, sometimes, ground conditions, tropical depressions and storms can maintain themselves hundreds of miles from their landfall point. 

With respect to Alberto, this system has a very large area of enhanced moisture to work with that extends from the Great Lakes to the western Atlantic and southward to the Caribbean. 

Alberto worked out the dry air that impinged on its ability to intensify over the Gulf of Mexico and created it's rather ragged appearance in the days leading up to landfall. 

(MORE: Brown Oceans Can Support Tropical Storms)

In addition to abundant moisture wrapping into Alberto's circulation, favorable upper-level winds helped to keep its spin alive. 

Alberto's envelope kept the winds blowing at all levels of the atmosphere at a nearly constant wind speed. This means that the system doesn't get blown over in one direction like it was in the Gulf of Mexico and in the Caribbean. 

(MORE: We've learned a few new things about the eye of a hurricane)

How Rare Is This? 

As Jon Erdman wrote about on Tuesday, tropical systems this far inland are not too rare. But it's a different story when we talk about tropical depressions. Only a handful of tropical depressions have passed through the southern Great Lakes, and none have passed directly over Lake Michigan. 

Tropical Depression Candy came closest to that lake in 1968, according to Brian McNoldy, a research meteorologist at the University of Miami. Its track is highlighted below in white. 

In rare cases, these systems can even intensify as they move inland. This was the case in 2007 when Tropical Storm Erin reintensified over Oklahoma after making landfall on the central Texas coast. It made landfall with maximum sustained winds of 40 mph. 

(MORE: Alberto's Early Formation Has No Bearing on How Active the 2018 Hurricane Season Will Be)

By the time the system reached central Oklahoma, it intensified into a cyclone with sustained winds of 60 mph – faster than any other time in the storms life cycle. Erin even developed an eye for a few hours as it passed Oklahoma City.

This period of intensification was short-lived and driven by another fast-moving weather feature, but the effects of rain and damaging winds were just the same on the ground. 

It seems to take just the right kind of conditions to get these systems this far inland.