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1-minute GOES-18 imagery to monitor flash flooding potential across American Samoa

By Scott Bachmeier •

1-minute GOES-18 Infrared Window (10.3 µm) images centered on Pago Pago (METAR identifier NSTU), from 1910 UTC on 18 May to 0200 UTC on 19 May [click to play MP4 animation]

During a period when American Samoa had been under a Flood Watch, the Weather Service Office at Pago Pago requested that a GOES-18 (GOES-West) Mesoscale Domain Sector be positioned over the region — due to their lack of radar, more frequent satellite imagery can be a critical tool for monitoring the development of deep convection. 1-minute GOES-18 Infrared imagery (above) showed clusters of deep convection that moved across the main island of Tutuila during a 7-hour period on 18-19 May 2026. At the Pago Pago METAR site on Tutuila (NSTU), most of their calendar day 24-hour precipitation for 18 May (5.21 inches) occurred in a 3-hour period during the GOES-18 animation shown above — and several Flash Flood Warnings were issued amid a variety of Local Storm Reports of flooding.

After a small cluster of convection rapidly developed just west of Tutuila shortly before 0000 UTC on 19 May, an overshooting top exhibited an infrared brightness temperature of -80.4ºC at 0018 UTC (below). Convective clusters then produced a thunderstorm with heavy rain showers at Pago Pago during the 0100-0200 UTC time period (METAR observations), contributing to much of the 4.15″ of rainfall that occurred during the 3-hour period ending at 0300 UTC.

GOES-18 Infrared Window (10.3 µm) image at 0018 UTC on 19 May, with a cursor probe of an overshooting top infrared brightness temperature [click to enlarge]

In a comparison of 1-minute GOES-18 Visible and Infrared images (below), the overshooting tops of rapidly-developing convective clusters that moved over and near Tutuila were very apparent. The violet pixel in the 0020 UTC infrared image highlighted an overshooting top brightness temperature of -81.0°C.

1-minute GOES-18 Red Visible images (0.64 µm, left) and Infrared Window images (10.3 µm, right), from 2340 UTC on 18 May to 0132 UTC on 19 May [click to play animated GIF]

Categories: GOES-18, Heavy rain / flooding, RealEarth