The animation above, of GOES-16 Visible (0.64 µm) imagery, shows Tropical Storm Kate at sunrise with convection near the storm center and to its east. (An overnight image from Suomi NPP’s Day Night Band, below, taken from NASA Worldview, also shows convection near the storm center.) As the day progresses, however, the obvious surface circulation moves northward and the convection near the surface collapses.

The shear analysis from the CIMSS Tropical Website, below, shows why the convection is displaced to the east of this storm. Strong westerly shear is present.

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Day Night Band imagery from the VIIRS (Visible Infrared Imaging Radio-Spectrometer) instrument on Suomi NPP and NOAA-20 allows satellite-borne estimates of power outages after strong storms. The imagery from Suomi NPP (0740 UTC) and NOAA-20 (0830 UTC) (orbital paths can be viewed here) shows a sharp reduction in the amount of light normally present over southeast Louisiana. This is especially true around the city of Houma, in eastern Terrebonne Parish. Lafourche Parish also looks devoid of man-made light sources.

Of course, interpretation of this signal will always be complicated by thick clouds and rainfall, two things that ably attenuate man-made light as it moves up towards the satellite. GOES-16 10.3 Clean Window imagery for the same times as above, below, shows that much of the high cloudiness with the storm had moved north of metropolitan New Orleans by the times of the images above. New Orleans International Airport (KMSY) reported no rain after 0600 UTC (although ceilings remained low: between 500 and 800 feet); clouds were likely thick.

What does southeast Louisiana typically look like? The image below, from 28 August (clipped from the VIIRS Today site), shows the Gulf Coast region from Houston TX (bright feature near the left edge) to Mobile and Pensacola on the right.

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

1-–minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above)  showed that Hurricane Ida gradually developed an eye, as the Category 1 storm intensified to Category 2 by 1800 UTC on 28 August 2021.

DMSP-17 SSMIS Microwave (85 GHz) image at 1235 UTC [click to enlarge]

Microwave (85 GHz) images from DMSP-17 (above) and DMSP-16 (below) — from the CIMSS Tropical Cyclones site — provided 2 views of the eye and eyewall structure at 1235 UTC and 2205 UTC, respectively.

DMSP-16 SSMIS Microwave (85 GHz) image at 2205 UTC [click to enlarge]

Ida was moving across very warm water (SST | OHC) — and was forecast to pass over an area of very high Ocean Heat Content associated with a warm eddy that was shed from the Gulf of Mexico’s Loop Current. Ida was also moving through an environment of low wind shear (below), which favored further intensification as it continued to approach the Louisiana coast.

GOES-16 Infrared images, with contours of deep-layer wind shear at 20 UTC [click to enlarge]

===== 29 August Update =====

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

Ida reached Category 4 intensity at 0600 UTC on 29 August; 1-minute GOES-16 Infrared and Visible images (above) depicted a well-defined eye during the hours leading up to the hurricane making landfall along the coast of Louisiana at 1655 UTC.

GMI Microwave imagery at 1510 UTC (below) portrayed a closed eye, with the heaviest precipitation located within the eastern semicircle of Ida.

GMI Microwave (85 GHz) image at 1510 UTC [click to enlarge]

A closer view of 1-minute GOES-16 Visible images (below) revealed the presence of low-level mesovortices within the eye of Ida — a feature often observed with high-intensity tropical cyclones. The mesovortices persisted as the hurricane moved inland, as Ida was slow to weaken. Just east of the eye, Galliano (KGAO) reported wind gusts as high as 85 knots (plot | text), before observations ceased after 21 UTC (presumably due to power outages).  A separate mesonet station at Galliano recorded a wind gust of 122 mph (NWS New Orleans tweet | plot); a ship reported a wind gust of 194 knots (tweet).

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

The MIMIC Total Precipitable Water product (below) showed that Ida was transporting rich tropical moisture northward across the central Gulf of Mexico coast of the US, raising a threat for flooding rainfall. 

MIMIC Total Precipitable Water product, 28-29 August [click to enlarge]

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At 1400 UTC on 27 August, strengthening tropical storm Ida sat south of Cuba, near the Isle of Youth, and is shown above in both visible and infrared imagery; brightness temperatures are as cold as -87 C in the image above. Note also that the surface circulation is southeast of the coldest cloud tops, perhaps as a result of the shear (click here; analysis from the CIMSS Tropical Website) over the system. (Added: Ida made landfall as a hurricane on the Isle of Youth at 1800 UTC).

Perhaps not surprisingly, the convection in/around the tropical cyclone is diagnosed by a Turbulence prediction product (developed using machine-learning incorporating water vapor imagery, GFS stability, and airline observations of EDR (eddy dissipation rate)) as a very likely region of turbulence. This turbulence product is also available online here (where turbulence observations are included) where it looks like this.

For more information on Hurricane Ida, including its potential threat to the central Gulf Coast late in the weekend, refer to the National Hurricane Center.

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