What Happened to Hermine?

The impacts of Hurricane Hermine were certainly less than expected, which is undoubtedly a good thing, especially for people who live along the coastline. However, many people are left wondering, “What went wrong with the forecast?” The strong winds and flooding rainfall were replaced by mostly sunny skies and comfortable temperatures. Even at the shore, the storm surge flooding was several feet less than anticipated, and only reached minor levels for most locations.

To understand what went wrong, you need to understand the background. This storm originated off of the coast of Africa and formed into tropical storm Hermine in the Gulf of Mexico, gradually strengthening into a category one hurricane before making landfall along the Florida Panhandle. The storm continued moving northeastward through the Carolinas and exited off of the North Carolina coastline. As the storm continued east of the Delmarva, we expected the storm to turn back westward, and drift back towards the Mid-Atlantic coast on Sunday and Labor Day Monday. However, as everyone knows, the storm never really got that close. So what happened?

Meteorologically speaking, an upper level disturbance dropping down from the Great Lakes was forecast to “capture” Hermine (seen in photo below). Hermine would then "dumbbell" around the upper disturbance (blue X), slingshotting the storm into or very near the Delaware & New Jersey beaches. The problem was that Hermine carried too much forward momentum and was able to escape farther out to sea before being pulled back towards the coast by the fairly weak upper disturbance. This allowed for track farther east, and less of an impact for the Northeast shores.

Many people have questioned the original forecasts, saying they were “over-the-top” or “fear mongering”, which couldn’t be farther from the truth. With less than 48 hours before the start of the system, we had strong model agreement regarding both the track and timing. All reliable models (including the beloved European Model) were pointing to a dangerous situation over the Labor Day weekend.

In fact, tidal forecasts predicted high water marks of historical proportions for many places due to the long term onshore flow and the close proximity of the previous New Moon tide cycle. For instance, Atlantic City, NJ tidal predictions (below) were expected to reach about 9.2 feet from a 4.0 - 4.5 foot storm surge. If these numbers were realized, 9.2 feet would have been the highest tide in recorded history. For reference, this forecast would break the 9.0 foot record back in December of '92 and Sandy's tide of 8.8 feet. 

While most meteorologists knew there was always a bit of uncertainty, waiting any longer to produce forecasts would waste valuable time for people, towns, and communities trying to make necessary preparations to save life and property. Even though Hermine's forecast was ultimately wrong, deep down most are grateful the historic flooding predictions didn't come true, as extreme damage, loss of life, and a long clean-up effort would have certainly resulted.