Overpasses from NOAA-20 (0601 and 0741 UTC) bracket an overpass from Suomi-NPP (0651 UTC), above, to provide excellent night time visual imagery animation over Hurricane Henri as it moved northward towards landfall over southern New England. It is difficult to pinpoint the center of the storm in this imagery. Per the National Hurricane Center, the 0600 UTC location was at 39.3 N, 71.0 W.

Radar imagery at 1143 UTC on 22 August, below, shows the storm south of Block Island

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GOES-16 Visible imagery (from CSPP Geosphere) just after sunrise on 22 August show the storm affecting much of Southern New England.

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Tropical Storm Henri intensified to become a hurricane at 1500 UTC on 21 August 2021  — and 1–minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images and “Clean” Infrared Window (10.35 µm) images (above) showed Henri during the 1400-2300 UTC period. Visible images indicated that a small-diameter inner core began to form later in the day.

Henri was moving through an environment of light to moderate deep-layer wind shear, as seen in an animation of GOES-16 Infrared images from the CIMSS Tropical Cyclones site (below),

During the preceding nighttime hours, a toggle between Suomi NPP VIIRS Infrared and Day/Night Band images at 0710 UTC (below) showed a large convective burst east of the surface center.

 

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Training thunderstorms early Saturday caused historic rains and devastating (and deadly) flash floods early on Saturday morning 21 August 2021. (Click here for a listing of hourly precipitation totals at McEwen, TN; this excellent tweet from Tomer Burg shows the radar in the region). Were there satellite products that described the environment, rich in moisture, that allowed the flooding rains to occur? The animation above shows MIMIC Total Precipitable water at hourly timesteps from 1000 UTC on 20 August 2021 to 1200 UTC on 21 August 2021. There is a pronounce gradient in moisture established over middle Tennessee by 0400 UTC on 21 August, and the amount of moisture is very large!

The rain that fell is analyzed below (data source: MRMS). The heavy rain caused drastic (and record-setting) stream flows and water heights on the Big Piney River. The flooding also closed I-40 temporarily.

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The animation below shows the GOES-16 Low-level water vapor imagery. A pronounced boundary is apparent near the region where the flooding rains developed. (Band 8 imagery — upper-level water vapor infrared (6.19 µm) imagery — shows a gradient in the same region as well)

GOES-16 Band 13 Clean Window infrared (10.3 µm) imagery, below, overlain on top of the Level 2 Total Precipitable Water (TPW) product document the development of the training thunderstorms along the TPW gradient. The motion of the storms is along the gradient. Numerous blog entries at the Hazardous Weather Testbed discuss how convective development is favorable along gradients, and in this case the developing thunderstorms maintain access to the moisture.

Derived Motion Winds can be used to estimate the winds surrounding the developing convection, and the animation below, from 0000 to 0956 UTC, show primarily northwesterly flow, so if the storms are moving with the ambient flow — and there’s no guarantee that that’s happening — you can infer their motion. Derived motion winds in the vicinity of the developing storms are primarily northwest and north-northwest. That might help a forecaster anticipate training with convection.

How do you know when anticipated thunderstorms within a primed region are ready to erupt — especially at night when visible imagery are unavailable (except for Day Night Band imagery; with Suomi-NPP (flying over at 0641 UTC and NOAA-20, flying over at 0720 UTC you can get a 50-minute animation in the middle of the night, shown here, with data from VIIRS Today). The animation below, of the GOES-16 Night Time Microphysics RGB, follows an example discussed here by Carl Jones, WFO FGF. The appearance of red values in the RGB over west-central TN around 0501 UTC heralds the development of deeper convection. This should also be the time when GLM lightning observations develop. See the second animation below.

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It turns out the relationship between color change in the RGB and lightning initiation isn’t quite so clear-cut. The stepping animation below shows the Night Time Microphysics and the GOES-16 Cloud Phase product. It is a challenge to relate a cloud phase to a particular color. GLM observations are occurring in regions where ice clouds are present. However, there are also regions where ice clouds are diagnosed and lightning is not happening.

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The Weather Prediction Center (WPC) had two Mesoscale Discussions on this event, here and here.

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This event was discussed at an FDTD Webinar (link) led by Matt Reagan and Brendan Schaper from the Nashville forecast office. (Storyboard Link)

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GOES-16 Visible Imagery, above, shows Tropical Storm Henri east of Florida and to the north of the Bahamas. Cirrus outflow is well-developed to the east and south, but the storm is sheared; the surface circulation is near the northwestern edge of the ongoing deep convection. Persistent northerly shear, as shown below in a figure taken from the CIMSS Tropical Website, shows Henri moving from a region of relatively high shear towards a region of relatively smaller shear.

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GCOM-W1 overflew Henri at 0616 UTC on 20 August. Microwave imagery, below, (retrieved from the AOML Direct Broadcast site) confirm the sheared nature of the storm at that time. Both frequencies show that deep convection is displaced to the south of the storm center.

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Suomi NPP overflew the storm at around 0600 UTC, and the toggle below shows the Day Night band visible (0.7 µm) imagery and the I05 infrared (11.5 µm) imagery; included in the toggle are Advanced Clear Sky Processor for Oceans (ACSPO) SST values in clear regions. Atlantic Ocean waters have surface temperatures in the 84-85º F range. Cloud top temperatures are as cold as -86º F for this overpass. (Suomi NPP VIIRS data were processed at the CIMSS Direct Broadcast site and injected into AWIPS).

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The animation of the Airmass RGB, below, shows a prominent feature over the mid-Atlantic states of the United States that will have a big role in Henri’s future path: a mid-tropospheric potential vorticity maximum highlighted as red/orange in the Airmass RGB. The toggle at bottom compares the 1211 UTC Airmass RGB with contours of pressure (mb) on the 1.5 PVU surface.

For the latest on Henri, refer to the National Hurricane Center Website. Residents of southern New England and Long Island and New Jersey in particular should pay close attention to this storm.

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