Monday, September 10, 2018

Hurricane Florence: 5 PM Monday Update

As of 4:00 PM CDT, Hurricane Florence remains a Category 4 Hurricane with sustained winds of 140 mph and gusts up to 165 mph. This places her in the middle of the Category 4 threshold.

As has been the case for most of the day, Florence continues to undergo rapid intensification. As of the latest update, Florence's central pressure has dropped to 939 millibars (mbs), which means it is a very strong low pressure system. In addition to the pressure drop, and due to the increase in the overall wind speeds, Florence's hurricane force winds now extend roughly 40 miles from the center.

Recent computer model guidance, along with current observations across the Atlantic environment, indicate that Florence is not done intensifying, and may reach very close to Category 5 intensity within the next 24 hours. But will she be this strong at landfall? Well, there are a few factors that may play against her favor.

First off is the "Eye replacement cycle" which is a common occurrence within many long-lived hurricanes. Basically, the eye of the hurricane undergoes a recycling process, which causes the hurricane to temporarily weaken a little bit. This may end up being the case when Florence nears landfall given the fact that she is such a long-lived hurricanes. Many hurricanes in their longevity can undergo this process two or three times on average during their lifetime.

Second off, right now Florence is a low shear environment; which means the atmospheric winds are not changing very much. Hurricanes like this, as it allows them to continue to intensify, but as Florence nears the North Carolina shoreline, the wind shear may increase a little bit, which may cause Florence to weaken a little bit before landfall.

So how strong may Florence be at landfall? At this time, it is difficult to tell. But latest guidance suggests that she will be at Category 4 intensity with winds between 140 mph and 150 mph, with even higher gusts.

In the previous post, I mentioned how when a hurricane weakens a little bit, it's wind field expands, and this may be the overall case, even if Florence only weakens a little bit.

As of right now, it appears that Florence will start picking up some speed as she rounds the base of a ridge of high pressure over the Atlantic. This means she will probably make landfall sometime on Thursday Afternoon or Thursday Evening.

Lastly, keep in mind that when a hurricane makes landfall, they begin to weaken very quickly. Often times what happens is that the ocean waters (which offer little friction to air) are where the winds will be highest, but the further you go inland, the more friction takes over and weakens the winds. This means that, although Florence may be a Category 4 Hurricane at landfall, it is entirely possible that most of the impacted areas will not see much of the 140 - 150 mph winds (especially further inland).

As of now, there are currently no watches or warnings in effect for the East Coast with regards to Hurricane Florence, however a hurricane watch may be issued on Tuesday Morning for the coasts of South Carolina and North Carolina.

-Timothy Albertson

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