Posted: 5:45 am Monday, September 17th, 2018
By Kirk Mellish
Florence certainly impacted Atlanta weather over the weekend but with little effect as expected with a few scattered thunderstorms late Saturday afternoon after a sunny start. Then a few showers Sunday with lots of clouds and humidity but cooler temperatures for most.
Yesterday the high temperatures ranged from 88 in Peachtree City to just 78 In Gainesville.
The lingering influence of Florence on the backside of the system means only a stray shower or thunderstorm in the Atlanta Metro area today or tomorrow, most of us will stay dry. Another week of August-like weather in store lasting right into at least early next week.
The historic and devastating rainfall in the Carolinas set new records with 30-40 inch amounts common and amounts of at least a foot widespread. Many major travel routes are impassable.
Six to nine trillion gallons of water has fallen on North Carolina alone with a couple trillion on South Carolina. Heavier rain than any previous tropical system in both states and worst flooding since Hazel in 1954.
Parts of SE North Carolina were under a TORNADO WATCH for 84 consecutive hours!
A tornado watch typically lasts around 4 hours.
Widespread river flooding will continue in the Carolinas for a week.
Going forward Florence will continue to weaken as its remnants head Northeast:
Some remnant energy from the system could actually loop back south in the Atlantic reaching Bermuda before it fizzles.
We will have to monitor the Gulf and Caribbean for any tropical development the next couple weeks but for the most part conditions are turning unfavorable as large scale divergence or lift and upward vertical motions in the atmosphere are replaced by neutral to negative. (Yellow is sinking air, green is rising air). The main Atlantic breeding ground shuts down from the same downward sinking air plus lots of dry air off of Africa:
Note conditions become more favorable for tropical development again as we end September and start October (seen above)
The Saharan air layer (SAL), is a dry and dust-filled air mass (about half the moisture of a typical tropical air mass) that pushes westward off Africa into the tropical Atlantic Ocean about every three to five days from late spring through early fall.
The SAL is typically located between 5,000 and 20,000 feet above the earth’s surface and is transported westward by bursts of strong winds that are located in the central and western Atlantic at altitudes between 6,500 and 14,500 feet.
It’s detected by special color coded weather satellite imagery and is easy to see as yellows, orange and reds (about the size of the Lower 48 states):
The SAL often helps to prevent or weaken tropical cyclones which feed off of the high humidity in the air of the tropics when not impacted by a SAL.
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