Dolly Becomes a Category 2 Hurricane – Not a Complete Surprise

Dolly has recently been upgraded by the National Hurricane Center (NHC) to a Category 2 hurricane on the Saffir/Simpson Hurricane Scale as it is about to make landfall on the South Texas coast.  None of the official NHC deterministic forecasts called for Dolly to intensify beyond Category 1 status.


However, just as “we should not focus on the skinny black line” for track forecasts, we should also not focus on the deterministic intensity forecast.  We need to understand that we will never be able to give a perfect forecast for track or intensity.  And the NHC has been very honest about that.  Along with each deterministic forecast from the NHC, probabilistic forecasts for the track and intensity are also issued.


I have been looking at the computer intensity guidance on Dolly that the NHC forecasters had available in real time.  None of this guidance consistently indicated that Dolly would reach Category 2 intensity.  The Intensity (Maximum Wind Speed) Probability Tables that have accompanied each forecast over the past 2 days have been showing a 10 to 18% probability that Dolly could become a Category 2 hurricane.  And the NHC teaches emergency managers to plan on the possibility of one category stronger than forecast for a landfalling hurricane.


Dolly’s intensification is yet another reminder that one should not focus on deterministic forecasts alone.


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