Understanding Rapid Intensity Changes in Official Hurricane Intensity Forecast Error Distributions

The characteristics of official National Hurricane Center (NHC) intensity forecast errors are examined for the North Atlantic (NA) and East Pacific (EP) from 1989-2017. It is shown how rapid intensification (RI) and rapid weakening (RW) influence yearly NHC forecast errors for forecasts between 12 to 48 hours in length. In addition to being the tail of the intensity change distribution, RI and RW are at the tails of the forecast error distribution. Yearly mean absolute forecast errors are positively correlated with the yearly number of RI/RW occurrences and explains roughly 20% of the variance. The higher occurrence of RI and RW events in the EP contributes to higher intensity forecast errors. Statistically significant improvements to 24-h RI forecasts have been made in the EP and to 24-h RW in the NA; however, little to no improvements have been made to RI forecasts in the NA and RW forecasts in the EP. Environmental predictors from the Statistical Hurricane Prediction Scheme (SHIPS) are used to diagnose what conditions lead to the largest RI and RW forecast errors on average. The forecast error distributions widen for both RI and RW when tropical disturbances experience low vertical wind shear, warm sea surface temperatures, and high low-level relative humidity. Consistent with previous work, the forecast error distributions suggest that improvements to our observational capabilities, understanding and prediction of inner-core processes is paramount to both RI and RW prediction.