DISCUSSION: On Saturday, September 1, Tropical Storm Florence was officially declared a tropical storm just west of the Cape Verde Islands in the Atlantic Ocean. The storm started as a tropical wave over Senegal in Western Africa which was first detected on August 28 as an area of low pressure. Florence then became Tropical Depression Six as it crossed over warm water and gained momentum over the Cape Verde Islands on Friday, August 30. Florence is the sixth named storm in a hurricane season which has had a large amount of Saharan dust which has led to an increased persistence and depth in the level of dry air in the atmosphere for much of the summer. This layer of dry air inhibits the formation of hurricanes over much of the Tropical Atlantic Basin in most circumstances.
On Wednesday, September 5, Florence gained strength from a Category 1 hurricane to a major Category 4 hurricane with windspeeds of 130 mph. By the rapid intensification, Florence officially becomes the first hurricane of the season to be at Category 3 or higher. Florence increased in intensity due to warmer sea-surface temperatures as well as encountering low vertical wind shear. Sea-surface temperatures are one of the key components as warmer sea-surface temperatures lead to higher amounts of evaporation which then leads to condensation and the release of heat which leads to even more water being evaporated. A low shear environment is the other key fundamental ingredient for hurricanes as a high amount of vertical wind shear would often have the effect of disrupting and tearing apart convection within the core of a hurricane due to the change in both wind speed and wind direction. However, Florence encountered strong directional shear on Thursday, September 6, as an area of high pressure to the north weakened and moved away which in turn also decreased the wind speed. The shear and decrease in wind speed led to Florence being downgraded from a Category 4 hurricane to a Tropical Storm on September 6.
The latest forecast track from the National Hurricane Center (NHC) has Florence traveling west-northwest re-gaining strength. The newest track has Florence going towards the eastern coast of the United States with much of the southeast from Florida to Virginia within the cone of uncertainty. The cone of uncertainty is the cone which shows the area where the different models forecast the area where the tropical cyclone will travel with the edges being the most extreme models. The regain in strength is due to a decreasing shear and a climb in sea-surface temperatures in its west-northwesterly course. The tracks for much of the past few days had Bermuda possibly being hit before Florence hit the large area of shear on September 6. As of right now, there are no warnings as Florence is not expected to come close to land until at least Wednesday, September 12.
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© 2018 Meteorologist JP Kalb