A sequence of VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images from Suomi NPP and NOAA-20 as viewed using RealEarth (above) showed “Storm Hannah” as it approached Ireland and the United Kingdom on 26 April 2019. The midlatitude cyclone had peaked in intensity as a Hurricane Force low around that time (surface analyses).

EUMETSAT Meteosat-11 Water Vapor (6.25 µm) images (below) showed winds gusting to 40-65 knots at several sites in southern Ireland and southern England, as the dry slot air stream moved across the region. In Ireland the peak wind gust was 66 knots at Mace Head, with 64 knots at Shannon — wind gusts in southern England included 71 knots at Aberderon, 68 knots at Pembrey Sands and 52 knots at Valley.

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EUMETSAT Meteosat-8 Visible (0.8 µm) images (above) and Infrared Window (10.8 µm) images (below) showed Category 4 Cyclone Kenneth (12 UTC JTWC advisory) making landfall along the northeast coast of Mozambique (north of Pemba FQPB: surface observations) on 25 April 2019. Kenneth had been moving over warm water and through an environment of low deep-layer wind shear, factors favorable for its rapid intensification (ADT | SATCON). After making landfall, Kenneth rapidly weakened to Category 1 intensity by 18 UTC — but Metop-A ASCAT winds of 40-49 knots were still sampled along the coast on the rear periphery of the storm. The slow inland movement of the remnants of Kenneth combined with copious amounts of tropical moisture as depicted by MIMIC TPW posed a concern for potential flooding problems.

VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images from Suomi NPP and NOAA-20, viewed using RealEarth (below), provided higher-resolution views of Kenneth a few hours prior to landfall. This was the strongest tropical cyclone landfall on record for the northern portion of Mozambique, as discussed here.

GCOM-W1 AMSR2 Microwave (89 GHz) image (below, courtesy of William Straka, CIMSS) showed the eye and spiral band structures near the Mozambique coast at 1030 UTC on 25 April. The evolution of the eye since its initial formation on 23 April was evident in the MIMIC TC product.

A longer animation of Meteosat-8 Infrared images (below) during the later half of its storm track showed the formation of an eye as Kenneth began its period of rapid intensification on 24 April. Cloud-top infrared brightness temperatures were -90ºC and colder (yellow pixels embedded with darker shades of purple) during the 1030-1800 UTC period on 24 April. Note that the center of Kenneth passed just north of the island of Grande Comore soon after the eye had developed — at Prince Said Ibrahim International Airport FMCH in Moroni, southeast winds gusted to 65 knots at 21 UTC 0n 24 April as the southern eyewall passed over the island.

NOAA-20 VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images (below, courtesy of William Straka, CIMSS) showed Kenneth at 2232 UTC on 24 April, shortly before the tropical cyclone had reached Category 4 intensity. Ample illumination from the Moon — in the Waning Gibbous phase, at 73% of Full — provided an excellent example of the “visible image at night” capability of the VIIRS Day/Night Band.

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GOES-17 (GOES-West) “Red” Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images (above) showed a number of ship condensation trails (or “ship tracks”) over the East Pacific Ocean on 24 April 2019. Aerosols from the exhaust of ships cause a “cloud seeding effect”, which results in a higher concentration of smaller cloud droplets compared to the surrounding unperturbed clouds. These smaller cloud droplets are more effective reflectors of sunlight, leading to a warmer (darker red) 3.9 µm signature.

GOES-17 Visible images (below) revealed a few eddy circulations within the marine boundary layer stratocumulus off the coast of southern California, along with other interesting Channel Island cloud interactions — some of the eddy circulations exhibited a small cloud-free center. Surface winds were light and variable over the Channel Islands (surface analyses), with a thermal low situated well inland over the Desert Southwest (the national high temperature on 24 April was 106ºF at Death Valley, California).

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GOES-17 (GOES-West) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) revealed orographically-trapped waves propagating westward against the ambient flow over the Haida Strait (between Haida Gwaii and British Columbia) in the wake of a cold frontal passage (surface analyses) on 22 April 2019. The waves initially formed downwind of the 2000-3000 foot terrain of Haida Gwaii, and moved eastward — but were then reflected back to the west by the higher 6000-8000 foot terrain farther inland over British Columbia.

Note that the wave signatures became more attenuated — especially over the southern portion of the Strait — as middle-tropospheric moisture began to overspread the area. This moisture at higher altitudes absorbed radiation being emitted from below, and re-radiated energy at the colder temperatures found within that layer of mid-level moisture.

A plot of GOES-17 Water Vapor weighting functions calculated using 00 UTC rawinsonde data from Annette Island, Alaska (below) showed significant contributions for Band 10 (7.3 µm, violet) and Band 9 (6.9 µm, blue) radiation coming from within the 700-850 hPa range, so it’s likely that many of the waves resided within that layer. Higher-altitude contributions from the 500-600 hPa layer were due to the aforementioned high-level moisture that later moved over the region.

In a toggle between Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 2137 UTC (below), cloud-top infrared brightness temperature of cloud features in the Haida Strait were generally in the -5 to -10ºC range, corresponding to altitudes of 4400-6400 feet (1.4-2.0 km, 850-780 hPa) on the 00 UTC Annette sounding. On 2140 UTC GOES-17 Water Vapor imagery, the waves were still apparent in the 7.3 µm image but were becoming less distinct in the 6.9 µm and 6.2 µm images due to the arrival of mid-tropospheric moisture.

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