Why do Slow-Moving Hurricanes Pose a Greater Threat?

The 2019 Atlantic Hurricane season officially ends November 1st, but as we are winding down from the peak of the current season, it is important to understand and revisit past seasons. According to the National Hurricane Center, the United States isn’t bracing for any major hurricanes to make landfall. But in the beginning of this month, Hurricane Dorian was a major hurricane that was thought to be headed for Florida. Instead of hitting the sunshine state, however the storm tracked over the Bahamas instead. By analyzing another slow moving hurricane from the 2017 season, this can give us an idea of why Dorian was so catastrophic. 
 
In 2017, Hurricane Harvey hit the Texas coastline, specifically Aransas County. When it made landfall, the storm was at its peak intensity. It was the first storm to make landfall in the United States as a category four storm – major hurricane – since William in 2005. While not getting into the specifics of how Harvey became a hurricane, this article will talk about how slow it moved over Texas, and how much damage was associated with it. 
 
When Hurricane Harvey hit, Aransas County was smashed with wind gusts of up to 132 mph. As a result, nearly every building was damaged. Not only in Aransas, but a major part of Texas received record breaking amounts of rainfall. This is what made the storm so impactful. The slow moving nature of the storm allowed for many days of heavy rainfall. On top of the storm surge associated with the storm, places were getting battered with upwards of 30 inches of rain. Some places, like Nederland, TX  got up to 60.58 inches of rain. That is five feet of rain in less than a week! This made rivers, roads, and houses flood. A lot of this rain was caused by Harvey stalling and sitting over Texas for an extended amount of time. The hurricane stalled over Texas for two whole days and produced so much rain which was unprecedented. The high amounts of rainfall put the town into distress, with insane flooding. Then it moved out to towards the Gulf of Mexico again, and while sitting out there, the storm, yet again, stalled again. This once again produced heavy rainfall rates for the Houston area for another two more days. It then made landfall again in Louisiana where it brought more than 14 inches of rain.
 
Due to large scale flows and weather patterns already in place, Harvey was stalled over Texas. This is what made the storm so deadly to the state. If this storm moved through quickly and then dissipated, then there wouldn’t have been as much rainfall and flooding. Even though hurricanes can cause serious damage, when they stall over a land mass for an extended period of time, their damage can be catastrophic. 
 Harvey was one of the costliest hurricanes that hit the United States.
 
Relating this back to now-a-days, Dorian’s eye made landfall on Abaco Island of the Bahamas with sustained winds of 185 mph. This was the strongest hurricane on record to hit the Bahamas. Dorian moved ever so slowly and the eye made landfall on the Grand Bahama Island, as a category five hurricane. The hurricane then stalled and sat over the Grand Bahama island for a whole day. Dorian’s eye then moved off the island on September 3rd. The eyewall of the storm has the strongest winds within a hurricane. It is within this location that you can find wind gust up to 200mph. With the eyewall sitting over Grand Bahamas for more than a whole day, the winds were completely ripping apart the island. The fact that this storms remained around the same area for such a prolonged amount of time, is what was responsible for the amount of damage that was done. 
 
 
With both of these hurricanes, it is important to understand that since they remained in relatively the same geological area (Harvey – over Texas, and Dorian – over the Bahamas) the amount of damage was greater than a hurricane that just passed quickly by. Always listening to the National Weather Service is important to do during a time of a storm like these. It is also important to listen to local and state enforcement. Emergency plans are created with these types of storms in mind, and the law enforcement, as well as the National Hurricane Center are there to keep the public safe. Both of these storms will go down in history, and will help make better forecast and preparations for the future. 
 
Credit: NWS, NOAA, NHC
 
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©2019 Weather Forecaster Allison Finch