The Garden Route Fires had been burning since about 24 October 2018 near George along the southern coast of South Africa (media story). On 29 October, EUMETSAT Meteosat-11 High Resolution Visible (0.8 µm), Shortwave Infrared (3.92 µm) and Longwave Infrared Window (10.8 µm) images (above) showed an elongated west-to-east oriented thermal anomaly or fire “hot spot” (red pixels) just northeast of George (station identifier FAGG) on Shortwave Infrared imagery during the hours leading up to the formation of a pyrocumulonimbus (pyroCb) cloud around 1300 UTC. The pyroCb exhibited the characteristic warm (+10 to +15ºC, darker gray enhancement) shortwave infrared cloud-top signature just off the coast at 1315 UTC, — this is due to enhanced solar reflection off ice crystals that are smaller compared to those of conventional thunderstorm tops.

Zooming out a bit to follow the southeastward drift of the pyroCb cloud (below), the coldest cloud-top 10.8 µm infrared brightness temperature (BT) was -61ºC (darker red enhancement) at 1315 UTC — then the cloud tops remained in the -55 to -59ºC range (orange enhancement) for the next 6 hours or so. Leveraging the large difference between cold 10.8 µm and warm 3.92 µm BTs, NRL calculates a pyroCb index, which classified this feature as an “intense pyroCb” (1315 UTC | animation). The coldest 10.8 µm cloud-top BT of -61ºC roughly corresponds to an altitude of 13.5 km based on 12 UTC rawinsonde data from Port Elizabeth (plot | list).

Imagery from NOAA-19 at 1420 UTC (courtesy of René Servranckx) also revealed the warm (dark gray) Shortwave Infrared pyroCb signature, along with a minimum cloud-top infrared BT of -58.1ºC (below).

A Suomi NPP VIIRS True Color Red-Green-Blue (RGB) image at 1230 UTC (below) was about a half hour before the formation of the pyroCb, but it did show a signature of smoke drifting southeastward off the coast.

On the following day (30 October), a NOAA-20 VIIRS True Color image (below) showed the classic comma cloud signature of a mid-latitude cyclone south of the coast, with the band of cold-frontal clouds extending northward across Lesotho. Note the thick plume of smoke spreading eastward within the strong post-frontal westerly winds.

A time series of of surface observations from George (below) supported the idea of a cold frontal passage: ahead of the front, temperatures rapidly rose to 104ºF/40ºC (with a dew point of 39ºF/4ºC) on 28 October about 1.5 hours prior to the formation of the pyroCb — then strong westerly winds (gusting to 40 knots/21 mps) with rising pressures and falling temperatures followed on 30 October.

The pyroCb research community believes that this is the first documented case of a pyroCb on the African continent.

 

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Now that skies have cleared up across South Texas, an interesting feature can now be seen on #GOES16 satellite. A flood wave from the heavy rainfall over the past few weeks can be seen flowing down the Nueces River. Check it! #txwx #stxwx pic.twitter.com/74n9penwKn

— NWS Corpus Christi (@NWSCorpus) October 27, 2018

As pointed out by NWS Corpus Christi (above), GOES-16 (GOES-East) Near-Infrared “Vegetation” (0.86 µm) images revealed an interesting flood wave moving along the Nueces River on 27 October 2018 (following a recent period of heavy rainfall).

A toggle between before (10 October) and after (27 October) Aqua MODIS False Color Red-Green-Blue (RGB) images from the MODIS Today site (below) showed dramatic differences between the amount of water (darker shades of blue) flowing along portions of the Nueces River on those 2 days.

A comparison of Suomi NPP VIIRS Visible (0.64 µm), Near-Infrared Vegetation (0.86 µm) and Near-Infrared Snow/Ice (1.61 µm) images from 27 October (below) demonstrated the improved land/water contrast of the Near-Infrared imagery, which makes it helpful for diagnosing certain types of flooding signatures.

===== 28 October Update =====

A toggle between GOES-16 Near-Infrared “Vegetation” (0.86 µm) images at 1552 UTC on 27 and 28 October (above) showed the advance of the flood wave during that 24-hour period.

A comparison of Suomi NPP VIIRS Near-Infrared “Vegetation (0.86 µm) and “Snow/Ice” (1.61 µm) images from the early afternoon hours on 27 and 28 October (below) displayed these 24-hour changes at a higher spatial resolution (375 meters, vs 1 km at satellite subpoint with GOES-16). The rear edge of the flood wave (located about 25 miles southeast of Cotulla) appeared to show up a bit better in the 0.86 µm images than the 1.61 µm.

Finally, in a toggle between 250-meter resolution Aqua MODIS False Color RGB images from 27 and 28 October (below), the advance of the leading edge of the flood wave can clearly be seen.

===== 29 October Update =====

GOES-16 Near-Infrared “Vegetation” images from 1552 UTC on 27, 28 and 29 October (above) showed the continued eastward movement of the flood wave down the Nueces River.

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After making landfall in the Northern Mariana Islands on 24 October, Super Typhoon Yutu underwent eyewall replacement cycles that brought about a drop to Category 4 intensity on 25 October. However, during the day on 26 October 2018 the storm again re-intensified to Category 5 (ADT | SATCON). Himawari-8 “Clean” Infrared Window (10.4 µm) images (above) showed a fascinating variety of storm-top features: (1) outward-propagating gravity waves, (2) a quasi-stationary (in a storm-relative sense, with respect to the moving storm center) curved “notch”  — resembling a hydraulic jump — within the eastern semicircle, and (3) periodic bursts of warm/cold couplets (black/violet enhancement)  — resembling “hot tower” impulses — located well northeast of the storm center (forming around 19-20º N/137º  W) that propagated quickly northwestward. In addition, cloud-top infrared brightness temperatures of -90ºC and colder (yellow pixels embedded within darker purple shades) were seen southern eyewall during the 18-19 UTC period (1834 UTC image).

A comparison of Himawari-8 “Red” Visible (0.64 µm) and Infrared Window images during the few hours after sunrise (below) showed an eye that was partially cloud-filled with low-level mesovortices.

An animation of Himawari-8 Visible images from 2302 UTC on 26 October to 0632 UTC on 27 October (below) provides a more detailed view of the mesovortices and some of the storm-top gravity waves. As was seen on Infrared imagery, a train of quasi-stationary concentric waves formed along the “notch” feature, becoming especially pronounced around 0532 UTC.

A comparison of DMSP-17 SSMIS Microwave (85 GHz) and Himawari-8 Infrared Window (10.4 µm) images from the CIMSS Tropical Cyclones site (below) showed Yutu around 2130 UTC.

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GOES-16 (GOES-East) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) revealed 2 types of terrain-induced features — mountain waves, and a banner cloud (reference 1| | reference 2) — across the Northeast US on 25 October 2018.

The mountain waves were more widespread and long-lasting, while the banner cloud formed to the lee of the White Mountains in New Hampshire and Maine (extending downwind as far as 100 miles). Mountain waves are often associated with turbulence; pilot reports of Moderate turbulence appeared in the vicinity of mountain waves over far eastern New York at 1202 UTC,  1417 UTC and 1742 UTC. A toggle between a 1009 UTC 6.9 µm Water Vapor image with the banner cloud and Topography is shown below; a later comparison at 1802 UTC showing widespread mountain waves can be seen here.

Strong winds were prevalent across that region in the wake of a storm centered over the Gulf of Saint Lawrence at 12 UTC — this storm produced as much as 5-12 inches of snow on the previous day in Vermont, New Hampshire and Maine:  NWS Burlington | NWS Gray | NWS Caribou — and the approach of a mid/upper-level jet streak (below). Winds gusted to 74 knots at Mount Washington, New Hampshire.

A comparison of 1-km resolution Aqua MODIS Water Vapor (6.7 µm) and Infrared Window (11.0 µm) images at 0648 UTC (below) showed that there were some areas where the mountain waves existed in clear air, with no clouds as an indicator of wave presence (for example, over western Maine).

A general lack of wave clouds over western Maine around that time was also evident on VIIRS Day/Night Band (0.7 µm) images (below) from Suomi NPP (at 0603 UTC) and NOAA-20 (at 0650 UTC). In this case, with ample illumination from the Moon — in the Waning Gibbous phase, at 99% of Full — the “visible image at night” capability of the Day/Night Band was fully realized.

Regarding the banner cloud which was present from about 0830-1700 UTC, the GOES-16 Cloud Top Height  and Cloud Top Phase products (below) indicated that the tops of the feature were around 24,000-25,000 feet (or 7.6 km, where the temperature was -43.1ºC on the 12 UTC Gray ME sounding: plot | text) and composed of ice crystals.

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