National Weather Service Pago Pago Facebook posts on 11 December describe an atmosphere primed for heavy rain and lightning, the latter Facebook also shown below. Band 13 animation, above, shows persistent deep convection over the Samoan Islands. The convection develops and drifts southward.

MIMIC Total Precipitable Water over the south Pacific shows moist air over Samoa being drawn poleward in an atmospheric river. (Cyclone Jasper (see this also) along the northeast coast of Australia is also apparent).

ASCAT Scatterometry data from Metop-B, below (source), shows strong surface convergence over the Samoan Islands.

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Lightning events on 12 December are shown below from this link. In this case, GOES-18 Flash Extent Density field are overlain on GeoColor imagery. Abundant lightning is occurring north and south of the Samoan Islands. An Airmass RGB animation from the same website (here), shows the persistent southward motion of moist tropical air over the Samoan Islands.

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Overlapping 1-minute Mesoscale Domain Sectors from GOES-16 (GOES-East) provided imagery at 30-second intervals during an outbreak of severe thunderstorms (SPC Storm Reports) across parts of the Mid-South and Deep South on 09 December 2023. “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) included time-matched plots of SPC Storm Reports for a  thunderstorm that produced a EF3-rated tornado which was responsible for 3 deaths and 62 injuries in the Clarksville, Tennessee (KCKV) area. The coldest cloud-top 10.3 µm infrared  brightness temperatures were in the -60 to -65ºC range (darker red enhancement).

1-minute GOES-16 Visible and Infrared images with/without an overlay of GLM Flash Extent Density (below) showed pulses of cold overshooting tops (brighter white infrared pixels) and brief lightning jumps associated with the Clarksville supercell thunderstorm as it moved across Montgomery County in Tennessee into Todd County in Kentucky.

30-second GOES-16 Infrared images (below) showed a later thunderstorm that produced a EF2-rated tornado which was responsible for an additional 3 fatalities in Madison, Tennessee (just north of Nashville KBNA).

1-minute GOES-16 Infrared images with/without an overlay of GLM Flash Extent Density (below) showed lightning activity associated with the thunderstorm that produced the Madison tornado (in Davidson County) — as with the Clarksville storm, pulses of cold overshooting tops and brief lightning jumps were observed as the tornadic thunderstorm progressed across the area.

Cursor sampling of 2-km resolution GOES-16 10.3 µm brightness temperature along with the operational Cloud Top Temperature and CLAVR-x Cloud Top Height derived products for the Clarksville TN tornadic thunderstorm and the Madison TN tornadic thunderstorm (below) indicated that Cloud Top Temperatures were in the -65 to -66°C range, with Cloud Top Heights in the 43000-45000 ft range (the CLAVR-x Cloud Top Height product was shown here, since its 2-km resolution was superior to the legacy 10-km resolution Cloud Top Height product currently available in AWIPS).

Those GOES-16 Cloud Top Temperature and Cloud Top Height values were a bit colder/higher than the Most Unstable air parcel Maximum Parcel Level (MU MPL) calculated using rawinsonde data from Nashville, Tennessee rawinsonde data at 1200 UTC on 09 December, shown below (source). Unfortunately, a 0000 UTC / 10 December Nashville rawinsonde report was not available.

A larger-scale view of 30-second GOES-16 Infrared imagery is shown below, spanning the ~13-hour period from 1900 UTC on 09 December to 0752 UTC on 10 December — which depicted more of the nighttime SPC Storm Reports across parts of northern Mississippi, Alabama and Georgia.

Many of these severe thunderstorms were developing within a corridor of moisture and instability ahead of an advancing cold front, as seen in 5-minute GOES-16 Visible images combined with Total Precipitable Water and Lifted Index / CAPE Derived Stability Indices in cloud-free skies (below).

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Target Sector (2.5-minute interval) JMA Himawari-9 AHI Clean Infrared Window (10.4 µm) images (above) showed the gradual development of a ragged eye with Cyclone Jasper as the storm moved southward across the Coral Sea on 07 December 2023. Intermittent convective bursts within the eyewall contained a few overshooting tops that exhibited infrared brightness temperatures around -90ºC (yellow pixels embedded within dark purple areas).

The partially-fragmented structure of the eyewall was evident in a DMSP-17 SSMIS Microwave image at 0816 UTC (source) (above) and a RCM-1 Synthetic Aperture Radar wind speed image at 0807 UTC (source) (below).

Himawari-9 Infrared Window (11.2 µm) images from the CIMSS Tropical Cyclones site (below) showed that Jasper was moving through an environment of low deep-layer wind shear — which, in addition to its motion across warm water (SST | OHC) favored continued intensification.

Jasper was upgraded to Category 3 intensity at 1800 UTC (JTWC discussion) — and a DMSP-17 SSMIS Microwave image at 1927 UTC (above) as well as a RCM-3 SAR wind speed image at 1914 UTC (below) displayed a more organized eyewall structure.

Jasper was subsequently upgraded to a Category 4 storm at 0000 UTC on 08 December (SATCON), as the satellite presentation of the eye improved in Himawari-9 Infrared images — and mesovortices within the eye were revealed in Visible images (below).

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A sequence of 5-minute CONUS Sector GOES-18 (GOES-West) Lower-level Water Vapor (7.3 µm), Mid-level Water Vapor (6.9 µm), and Upper-level Water Vapor (6.2 µm) images (above) revealed the diurnal cycle of nighttime cooling and daytime warming at the summits of Mauna Kea and Mauna Loa on the Big Island of Hawai’i on 06 December 2023. This case is another example which helps to underscore the fact that Water Vapor spectral bands are essentially Infrared bands, which — in the absence of clouds, and in a dry atmosphere — can sometimes sense surface features.

The presence of very dry air within most of the middle/upper troposphere over Hawai’i on 06 December had the effect of shifting the water vapor weighting functions to lower altitudes, as seen on plots for the 3 ABI Water Vapor spectral  bands calculated using rawinsonde data from Hilo PHTO (below). This allowed thermal radiation from the higher terrain of Mauna Kea and Mauna Loa to pass upward — with minimal attenuation — through what little high-altitude moisture was present, and reach the 7.3 µm / 6.9 µm / 6.2 µm detectors on the GOES-18 ABI instrument. The 2 mountain summits extend upward to near the 600 hPa pressure level — close to the level of peak weighting function contributions for Water Vapor spectral bands 09 and 10 — and to an altitude where there was still a contribution from the Band 08 weighting function, as calculated using the Hilo soundings.

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