GOES and GPM Capture Florence Trying to Intensify Over the Atlantic
Released on September 12, 2018
Hurricane Florence originally formed from an African Easterly wave that emerged off the west coast of Africa back on the 30th of August. When it reached the vicinity of the Cape Verde Islands the next day, it was organized enough to become a tropical depression. The following day the depression strengthened enough to become a tropical storm and Florence was born on the 1st of September. Over the next 3 days, Florence gradually strengthened as it moved in a general west-northwest direction into the central Atlantic. Then, on the 4th of September, Florence began to rapidly intensify. By the morning of the 5th, Florence was a Category 3 hurricane before reaching Category 4 intensity later that afternoon with maximum sustained winds estimated at 130 mph by the National Hurricane Center (NHC). At this point, Florence became the victim of increasingly strong southwesterly wind shear, which greatly weakened the storm all the way back down to a tropical storm the by evening of the 6th.
The following GOES-East Infrared (IR) loop shows Florence from 17:54 UTC (1:54 pm EDT) 6 September to 19:27 UTC (3:27 pm EDT) 7 September when it was struggling against the strong southwesterly wind shear in the Central Atlantic. A very interesting looking feature is the arc-shaped cloud that propagates outward from the storm towards the west. This cloud feature is occurring at upper-levels and is likely tied to a gravity wave propagating outward from an area of intense convection that erupted from deep within the storm. When the tops of these smaller scale storms within a storm reach the upper troposphere, they can trigger gravity waves. As these waves progagate outward they can enhance cloud formation where they induce rising motion and erode cloud where they induce downward motion or subsidence. As this arc-shaped cloud is able to propagate outward uniformly from the center, it must be occurring above the shear layer. Compensating areas of subsidence can also surround the strong rising motion occurring within the tall convective clouds. This can help to erode surrounding clouds and may be contributing to the clearing that occurs between the arc-shaped cloud and the main area of convection.
The end of the loop shows surface rainfall and a 3D flyby of Florence courtesy of the GPM core satellite, which passed over the storm at around 19:21 UTC (3:21 pm EDT) on the 7th. At the surface, two areas of intense rain (shown in magenta) reveal the presence of two areas of strong thunderstorms within Florence north and northeast of the center. The flyby shows a 3D rendering of the radar structure of the storm. The darker blue tower indicates an area of deep convection that has penetrated well over 10 km high and is associated with the southernmost area of intense rain just north of the center. It is these areas of deep convection that fuel the storm by releasing heat, known as latent heat, mainly from condensation, near the core. Although it would be nearly 2 days before Florence re-gained hurricane intensity, these convective towers are what helped Florence to survive the effects of the wind shear and eventually grow back into a Category 4 hurricane.
GPM is a joint mission between NASA and the Japanese space agency JAXA.
Caption by Stephen Lang (SSAI/NASA GSFC) and Joe Munchak (GSFC).
GPM passed over Tropical Storm Florence on September 7, 2018. As the camera moves in on the storm, DPR's volumetric view of the storm is revealed. A slicing plane moves across the volume to display precipitation rates throughout the storm. Shades of green to red represent liquid precipitation. Frozen precipitation is shown in cyan and purple.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 220.127.116.11.0