Forecast of the Day • A National Weather Forecasting Contest

The forecasting of precipitation amount for specific locations can be very difficult, especially when there are thunderstorms which produce heavy rain in some places and little or no rain just a short distance away. Predicting rainfall from a tropical system is like that, because the track and speed of the storm is not certain, and the precipitation pattern around the system is not always simple and symmetric. So understanding that it won't be easy, let's try to predict Wednesday's 24-hr precip amount for Hattiesburg-Laurel Airport in Mississippi, as Tropical Storm Gordon approaches. Here is a a precipitation amount forecast from the National Weather Service, and you can see some NWS model predictions below.

Question: It's obvious why the track of a tropical system affects the expected precipitation amount at a given location, but how does the speed of the movement of the system also affect the amount?