Dear Tom, 
It always seems that when there is a big hurricane in Florida, we have beautiful weather in Chicago. Am I imagining this or is this true? I feel like it goes back all the way to Andrew in 1992. If there is a correlation, is it coincidental or is there a meteorological reason?

Thank you,
Mary Fisher

Dear Mary, 
You are not imagining this.  Quite often, but not always, U.S. landfalling hurricanes will occur about the same time Chicago enjoys a period of tranquil weather, sometimes accompanied by above normal temperatures. The reason is meteorological. Hurricanes are relatively large circulations that produce strong upward vertical motion in the atmosphere. Loops of satellite imagery can show how the atmosphere in the spiral bands and eye wall of the storm appears to be “boiling over”.  In order for the atmosphere to compensate for the mass of rising air within the storm, downward vertical motion must occur around the periphery of the hurricane. When air sinks, it compresses and warms, lowering the relative humidity and thus encouraging sunny, warmer-than-normal weather.  Hurricane remnants can also linger for days over the eastern U.S., slowing the normal west-to-east progression of mid-latitude systems and allowing pleasant weather to persist for days around the edges of the circulation.