Thunderstorms affecting American Samoa

June 20th, 2020 |

VIIRS Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP [click to enlarge]

VIIRS Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP [click to enlarge]

VIIRS Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP as viewed using RealEarth (above) showed thunderstorms beginning to increase in areal coverage north of and in the vicinity of American Samoa on 20 June 2020, as a surface trough north of the islands began to move southward.

To monitor the flash flooding potential of these thunderstorms, a GOES-17 (GOES-West) Mesoscale Domain Sector was positioned over the American Samoa region — which provided “Clean” Infrared Window (10.35 µm) images at 1-minute intervals (below). Some of these storms exhibited minimum cloud-top infrared brightness temperatures around -80ºC (black enhancement), producing heavy rainfall (over 6 inches in 9 hours) and strong winds (gusting to 60 mph) according to the NWS Pago Pago compilation of local storm reports.

GOES-17 "Clean" Infrared Window (10.35 µm) images [click to play animation | MP4]

GOES-17 “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

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