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We never thought we would be tracking a tropical system moving into our area here at KIMT, but the weather is full of surprises isn't it?
Yes, we are tracking a tropical cyclone moving into the upper Midwest. This is unprecedented.
Let's start off with silencing any rumors though...
This is not a hurricane rolling to the Midwest. By the time it rolls into Iowa Tuesday it won't even be strong enough to be considered a tropical storm. This is not going to be the strongest storm you have ever seen, and any flooding likely won't be the worst you have ever seen either. However, Cristobal still poses a flooding threat, along with strong storms expected Tuesday afternoon.
With that said, Cristobal will very likely still make it into the record books, and in fact it already has. It was the earliest the third storm of the Atlantic Hurricane season has ever formed, forming in the Gulf of Mexico on June 2nd. It will likely be the furthest north and west a tropical cyclone has ever tracked over the United States. As far as records go, no tropical cyclone has ever make it into Minnesota or Wisconsin, with the Great Galveston Hurricane of 1900 potentially having made it into southern Iowa as a Tropical Depression. Two former tropical storms have made it into Wisconsin as extra-tropical cyclones, still dropping rain along the way, but both only somewhat count. (Tropical cyclones differ form extratropical cyclones dynamically, with extratropical cyclones having cold and warm fronts - and being responsible for many of the blizzards we see during the winter months).
What we are seeing with Cristobal is not impossible though. In 2018, Tropical Storm Alberto made it all the way from the Gulf of Mexico into Michigan as a tropical depression. So we know it's possible, just incredibly rare.
Now let's talk more about what this means for us.
Cristobal will move into the upper Midwest Tuesday afternoon. It's center is forecast to move into Iowa sometime around noon Tuesday. At this time, Cristobal will likely still be tropical, and will thus still present some rain bands - a feature of tropical cyclones like hurricanes where thunderstorms line up and spin around the entire systems center. Some of these rain bands could move over our area as soon as noon Tuesday. Heavy downpours and gusty winds will be the concern here. If rain bands should run or train over the same area for an extended amount of time, flooding will quickly become a concern. Like everything with Cristobal though, this will be dependent on how far away the center of the storm tracks.
If Cristobal is tropical on Tuesday afternoon, you may notice that these storms just feel different. The air will not cool as much after it rains, and humidity will still remain.
Overnight Tuesday, Cristobal will begin to transition into an extratropical cyclone as it merges with a cold front approaching from the west. This will bring us cooler temps in Wednesday, but it will also serve to squeeze out more rain and strengthen the storms winds. Winds Wednesday will reach 25mph out of the northwest, with gusts above 30mph. Keep in mind, any change in the timing of the cold front Tuesday will impact the forecast.
Let's also breifly talk about Tornadoes. Tropical cyclones like Hurricanes can in fact spin up tornadoes. These tropical tornadoes most often occur on the right side of the storm relative to its motion. Lucky for us, we look to be on Cristobal's left side as its center marches towards Wisconsin. Tornadoes will be of low concern unless Cristobal manages to track a lot closer or even west of us.
Now it's time to talk about rainfall potential.
Tropical systems like Cristobal can carry an incredible amount of moisture with them, and merging a tropical cyclone with a cold front is a great way to squeeze out a lot of rain. So for us in the Midwest, rainfall and potential flooding is our greatest concern.
Models differ on rainfall amounts across our area. Both the European and RPM model bring 3+ inches to a wide swath of our area with more isolated higher amounts, while the GFS brings more in the range of 1-2 inches to us. How much rain wee see form Cristobal will depend on where exactly it tracks. The closer it tracks to us, the more likely we are to see more rain. Flooding will likely begin to occur when rainfall accumulations begin to top 3 inches, so we will have to monitor the track of Cristobal as it draws closer.
Feel free to contact KIMT with any and all weather questions.