Slow moving hurricanes are the worst. Not just for the impacts they cause, but for the headache they are to forecast. Most of the time , the National Hurricane Center forecast cone isn’t going to move all that much within 24 hours of a landfall. That wasn’t the case with Sally as the track had to be shifted eastward as Sally wobbled and lifted further northeast a little ahead of schedule.
The path this storm took was crazy! Look at all those zigs and zags. Slow moving storms like this are kind of like a spinning top on a flat table. You know it’s going to wobble around, but you can’t predict exactly where it’s going to wobble around.
The impacts are tough to get right in slow moving storms too. One of the toughest things to forecast correctly in tropical forecasting is storm intensity. Typically, a slow moving hurricane just off the Alabama coast won’t intensify that much, because it upwells cooler water from below, especially in the shallower waters on the Continental Shelf. This storm actually had “downwelling” instead. And that kept sea surface temperatures from cooling too much.
This is likely at least partially why Sally intensified a bit more than forecast prior to landfall. We’re going to be dissecting this storm for a while, because of how unusual it was, but Sally is a humbling reminder to all of us who work with extreme weather just how difficult storms can be to predict.