Florence approaches the coast

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Main Threats

No significant threats in sight

Summary

We will see very warm and humid conditions continuing today. In fact, that warm, muggy airmass will be with us right on through next week. Be careful if you have outdoor activities, as you can easily overheat when it’s this muggy outside.

We’ll also see isolated showers around, just as we did yesterday. When we get this warm and humid it doesn’t take much of a disturbance to trigger a shower.

By Sunday, the influences of Florence will begin to be felt, though only slightly. If Florence stays on her current forecast path (this is tricky) we’ll see rain Monday and Tuesday of next week. We will also have breezy conditions. At this time, we do not expect significant severe weather from Florence, as she will be so washed out by the time she reaches our neck of the woods.

Tropics

The headline today is Florence, as it should be. The storm has been downgraded to a category 2 hurricane, but that is little comfort to both North and South Carolina. Why? Because it’s not the wind that causes all the damage; it’s the flooding. Sure, wind is a big deal to coastal residents, they take the brunt of it. But the storm surge does so much damage that it’s hard to notice wind damage. It’s the flooding that everyone should fear.

Winds drop remarkably with contact with the land. Before the hurricane reaches shore, it has nothing but open water. Once interaction with land begins, the winds begin to slow down dramatically.

North Carolina’s record 24-hour rainfall is about 22 inches. Florence will shatter that into pieces. Remember what Harvey did to Texas last year? If you don’t remember that Florence will remind you when you see what happens to the Carolinas.

The storm is a cat 2 hurricane, with winds of 110 mph. A cat 3, which is considered a major hurricane, has winds of 111-130 mph. So, Florence is just below major hurricane status. However, the storm surge will be like that of a cat 3 or cat 4. That is because the storm is expected to stall along the coast, allowing strong onshore winds to pile up the water along the coast for a few days. The storm surge and inland flooding will likely be catastrophic. This is quite possibly the worst natural disaster North Carolina has ever faced.

I was looking at the lightning detection map this morning and noticed a very interesting pattern. The lightning is confined to the outer-most bands of Florence. This isn’t unusual for hurricanes. These storms are so warm at their core, with all that warm, hot air rising into the atmosphere and condensing. This causes there to be very little ice production in the clouds, which limits lightning production. Lightning is the result of charge separations between water (neg charge) and ice (pos charge). However, in the outer bands the cloud tops are colder and can produce more ice, leading to lightning.

I wanted to look at the lightning map for another reason, too. The only time hurricanes tend to produce lightning at their core is when they are strengthening. Why? We don’t know. But, it is encouraging to see no lightning at the core, which leads us to believe the storm is just holding steady at 110 mph. Not all storms produce lightning when they strengthen, so it’s not a fool-proof method for analysis. But, a lot of them do. Florence is currently in an environment favorable for a bit of strengthening, but over the past couple of days she has tended to use that extra power to grow larger, rather than increase her wind speeds. Some hurricanes just do that.

Below is our lightning map, notice the ring of lightning around Florence.

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Look at that water vapor map. Wow! That is a LOT of moisture, folks. Rainfall totals from this storm will likely exceed 40 inches in places. The storm is currently poised to make landfall near Wilmington. After that, the storm will slow to a crawl.

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The radar shows the eye quite well. Outer bands are beginning to move ashore this morning. For those who chose not to evacuate, the next 48 hours are going to be torture.

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I will briefly mention the other storms out there. Both Joyce and Helene are headed out to sea, thank goodness! The disturbance in the Gulf is disorganized again, reducing its chances of development to 50/50. We’ll still keep an eye on it.

Isaac is a little different. He is expected to weaken to a depression, but he’s also headed into the Caribbean and on a path that may lead him into the Gulf. Some models suggest the system could strengthen there, but confidence is too low to really broadcast that. Other models show it completely disintegrating. I’ll keep an eye on him.

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Records

We’ll briefly address this section today. Interestingly, on this day in 1979 Nashville broke their greatest one-day rainfall record (6.60″), as the remnants of Hurricane Fredrick moved across the midstate. A rainfall intensity record of 4.12″ in only three hours was also set for the city.

This reminds me, nearly every state that can be affected by tropical systems has rainfall records that were set by these systems. Tropical storms/hurricanes contain a phenomenal amount of moisture, and that is evident when looking at rainfall records.

Incidentally, there will never be another Fredrick because his name was retired. The hurricane lashed the Gulf Coast as a cat 4. At Gulf Shores, AL, 80% of the structures there were completely destroyed. Fredrick was a big one!

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You all have great day. I have been invited to speak to the Crossville Noon Rotary club at lunch today and tell them all about weatherTAP. They also want to know what a day in the life of Meteorologist Mark must be like (ha). Lordy, if every week were like this one they’d think I was the busiest man alive! Seriously, it’s a privilege to be invited to share my experience working for a place that is such a joy to work for.  Wish me well!

p.s. I thought, for some reason, there would only be 15-20 Rotary members at this lunch. Yesterday, I found out there will be 50-60!

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