Hurricanes bring significant destruction to the coastline that they impact. The impact is much more significant over and near where the eye makes landfall. Much of the coast though is spared the worst of the destruction. More of the coast will be at a threat before landfall due to the uncertainty of where exactly the hurricane will make landfall. This writing examines the reasons for the difficulty of predicting hurricane landfall. Uncertainty will be higher when the hurricane is a couple of days or more from making landfall. Generally a broader region of the coast will be in the threat area from the hurricane when it is far from land. As the hurricane approaches the coast, the region of threat is typically better and better defined. This is especially true for faster moving hurricanes that have well defined upper level steering mechanisms. What are some reasons why it is difficult to forecast landfall location? Besides a forecast being several days out, another reason is due to the shifting position of the eye. Eyewall replacement cycles can cause the center of the circulation to drift one direction or another. This can make it appear the hurricane is changing directions but often this shift is temporary. These shifts in direction though can cause the path to alter from what was expected. The convective storm dynamics in the eyewall can cause the center of circulation to be pulled one direction or another. On satellite, it can be noticed that the eye does seem to shift somewhat from the prevailing tendency that the eye has from time to time. Eyewall replacement cycles and storm dynamics in the eye wall play a role in this shift. Another reason for a change in hurricane track is due to changes in the steering currents that can also be difficult to forecast. The steering currents can be weak and subtle and thus any change in this steering will cause the hurricane track to change. Steering is influenced by upper level winds associated with troughs and ridges. If the steering is weak then often the hurricane will move slowly and it can be more difficult to anticipate how the steering will influence the storm in the future. A third reason can be due to a significant strengthening or weakening of the hurricane. When the hurricane changes in intensity then this is often accompanied by some sort of path shift. Interactions with land/islands, a very warm area of sea surface temperature, and upper level wind shear can cause the path to shift from the previous path. All these reasons cause it to be more difficult to forecast where a hurricane will make landfall. |