MADISON, Wis. - Tropical Depression Alberto is definitely a special storm.
Not only did the system form a week before the official start of hurricane season, but it continues to churn northward, bringing heavy rain to Wisconsin.
Additionally, it formed as a subtropical storm in the Gulf of Mexico. Subtropical storms have characteristics of tropical cyclones (that pull energy from warm ocean waters) and extratropical cyclones (a typical storm Wisconsin experiences that gains energy from temperature and humidity differences). But as the storm moved onto land, it actually transitioned to a tropical depression. This phenomenon is extremely rare.
It's also abnormal to see a tropical system anywhere near southern Wisconsin.
"The discernible circulation of the cyclone is so close to us," explained Jonathan Martin, UW Professor of Atmospheric and Oceanic Sciences.
"We're seeing an obvious center of the storm just a couple of hundred miles south of us, across northern Indiana, which is just unbelievable."
Alberto brought more than an inch of rain to Madison on Wednesday, bumping up the May rainfall total to 9.78 inches. That moves us into second place for all time in terms of May monthly rainfall.
However, the center of the storm was still hundreds of miles to the southeast of Madison. This is textbook tropical cyclone behavior, according to Martin.
"There's still a fairly substantial contribution to the importation of tropical water vapor content from Alberto, much farther north than the center of the storm. We're the recipient of that today with our little rain event, which was fairly impressive."
Couple that with the four day stretch of 90 degree weather we just escaped, and it has been a crazy weather week across southern Wisconsin.
So does that mean we can expect more tropical cyclones and high heat for the rest of the summer?
Martin says it's impossible to say.
We'll just have to wait and see.
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