Elsa briefly regains hurricane intensity before making landfall along the Florida coast

July 6th, 2021 |

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

Late in the day on 06 July 2021, Tropical Storm Elsa regained hurricane intensity as of 0000 UTC, just off the west coast of Florida. 1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed the tropical cyclone during the 1500 UTC to 0000 UTC time period. In the morning, cloud-top infrared brightness temperatures of -80ºC or colder were seen (violet pixels), but during most of the day they were in the -70 to -79ºC range. While Elsa had been moving over water with Sea Surface Temperature values around 28ºC, the Ocean Heat Content of those waters was relatively low.

For a few hours the low-level circulation of Elsa remained exposed from its deep convection to the northeast — and GOES-16 Visible images with an overlay of deep-layer shear at 1800 UTC, from the CIMSS Tropical Cyclones site (below), showed that this was due to westerly shear values around 25-30 knots over the area.

GOES-16 “Red” Visible (0.64 µm) images, with an overlay of deep-layer wind shear at 1800 UTC [click to enlarge]

GOES-16 “Red” Visible (0.64 µm) images, with an overlay of deep-layer wind shear at 1800 UTC [click to enlarge]

The center of Elsa moved just to the east of Buoy 42023 — a plot of wind speed/gust and pressure is shown below.

Plot of wind speed/gusts and pressure at Buoy 42023

Plot of wind speed/gusts and pressure at Buoy 42023

A DMSP-15 Microwave (85 GHz) Microwave image at 2155 UTC (below) indicated that Elsa had nearly completed the formation  of a closed eyewall at that time.

DMSP-15 Microwave (85 GHz) Microwave image at 2155 UTC [click to enlarge]

DMSP-15 Microwave (85 GHz) Microwave image at 2155 UTC [click to enlarge]

GOES-16 Infrared  / Water Vapor Difference images (below) revealed pockets of stronger overshooting tops near the center of deep convection during the hours leading up to Elsa reaching hurricane intensity.

GOES-16 Infrared / Water Vapor Difference images [click to enlarge]

GOES-16 Infrared  / Water Vapor Difference images [click to enlarge]

===== 07 July Update =====

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

After once again weakening to Tropical Storm intensity at 0600 UTC, Elsa eventually made landfall along the coast of Florida around 1500 UTC on 07 July, as seen in 1-minute GOES-16 Visible and Infrared images (above) — inland impacts included an EF0 tornado, wind gusts to 71 mph and rainfall exceeding 11 inches (NWS Public Information Statements).

At 1223 UTC, a DMSP-17 SSMIS Microwave image (below) indicated that a closed eyewall was not present with Elsa at that time.

DMSP-17 SSMIS Microwave (85 GHz) image [click to enlarge]

DMSP-17 SSMIS Microwave (85 GHz) image [click to enlarge]

Using Polar-Orbiting Satellite Imagery from Direct Broadcast sites to understand Elsa

July 6th, 2021 |

Suomi NPP Adapative Day Night Band imagery, 0636 UTC on 6 July 2021 (Click to enlarge)

AOML (The Atlantic Oceanographic and Meteorological Laboratory) maintains a Direct Broadcast antenna site that holds satellite imagery (created using CSPP — the Community Satellite Processing Package) created when a tropical system — such as Elsa — is within the download footprint of the AOML antenna.  This imagery — particularly in the microwave — is useful to describe the system’s structure. The Day Night Band image above, from Suomi NPP at 0636 UTC, shows a non-symmetric storm with the bulk of clouds to the east and south of the surface center (at that time near 23.9 N, 82.3 W, i.e., in the Florida Straits to the south of Dry Tortuga).  Rainfall, as diagnosed using MIRS algorithms and microwave ATMS (Advanced Technology Microwave Sounder) data from NPP, below, shows the asymmetry of the storm as well:  almost all the diagnosed rain is east of the center. (It’s helpful that both infrared imagers and microwave sounders are on the same satellite!)

Suomi NPP ATMS-derived Rain Rate, 0637 UTC on 6 July 2021 (Click to enlarge)

The GCOM-W1 (supported by JAXA) satellite also scanned Elsa shortly before 0700 UTC on 6 July.  Microwave observations at ~36 GHz, below, and at 89 GHz, farther below, can help to characterize the structure of the storm. Indeed, observations at/around 85-89 GHz are used in the MIMIC TC product as described here.

GCOM AMSR-2 observations at 36.5 GHz, 0649 UTC on 6 July 2021 (Click to enlarge)

GCOM AMSR-2 observations at 89.0 GHz, 0649 UTC on 6 July 2021 (Click to enlarge)

In addition to the AOML site, the CIMSS Direct Broadcast site contains Polar Orbiting imagery in near-real time. The afternoon 88.2 GHz image from (NOAA-20) ATMS is shown below.  Cold cloud tops associated with strong scattering by ice of the 88.2 GHz signal are apparent.

NOAA-20 ATMS Channel 16 Brightness Temperature, 1845 UTC on 6 July 2021 (Click to enlarge)


There are a multitude of polar orbiters such that observations show up in clusters of time.  However, for a better time animation, it’s still best to rely on GOES-16!  The animation below, from CSPP Geosphere, shows a sheared storm south and west of Ft Myers FL.  Indeed, an 1800 UTC 6 July 2021 shear analysis from the CIMSS Tropical website (here, from this site), shows westerly shear of 25-30 knots.

GOES-16 True-Color imagery, 6 July 2021 from 1730 to 1920 UTC (Click to animate)

For the latest information on Elsa, consult the webpages of the National Hurricane Center, or the SSEC/CIMSS Tropical Weather Page.