This website works best with a newer web browser such as Chrome, Firefox, Safari or Microsoft Edge. Internet Explorer is not supported by this website.

CIMSS Satellite Blog

MENU

Thunderstorms prompt the issuance of Flash Flood Warnings in American Samoa

By Scott Bachmeier •

1-minute GOES-18 Infrared images with an overlay of GLM Flash Points (white dots) and METAR surface reports (cyan), from 1501 UTC on 24 January to 0000 UTC on 25 January [click to play MP4 animation]

Due to a lack of radar coverage over American Samoa, WSO Pago Pago requested a 1-minute Mesoscale Domain Sector over the islands to monitor convective development and the potential for flash flooding. GOES-18 (GOES-West) Clean Infrared Window (10.3 µm) images (above) showed rain showers and thunderstorms that developed in the general vicinity of the American Samoa island of Tutuila (where Pago Pago International Airport NSTU is located) on 24 January 2026. GLM Flash Points indicated that intermittent lightning occurred near Tutuila — and thunderstorms were occasionally reported at NSTU. The development of deep convection was enhanced by the presence of a surface trough of low pressure across the area (1500 UTC | 1800 UTC | 0000 UTC).

The coldest cloud-top infrared brightness temperatures were in the -85 to -89ºC range (darker shades of purple embedded within brighter white regions) — which represented a slight overshoot of the Most Unstable (MU) air parcel’s Equilibrium Level (EL), according to a plot of rawinsonde data from NSTU at 0000 UTC on 25 January (below).

Plot of rawinsonde data from Pago Pago, American Samoa at 0000 UTC on 25 January [click to enlarge]

The GOES-18 Infrared image at 1850 UTC (below) included a sample of the corresponding NSTU METAR — which indicated that a thunderstorm with heavy rain showers was reducing the visibility to 3 miles at that time.

GOES-18 Infrared image at 1850 UTC on 24 January, with a cursor sample of the 1850 UTC Pago Pago (NSTU) METAR surface report [click to enlarge]

The GOES-18 Infrared image at 2058 UTC (below) included a sample of the corresponding NSTU METAR — which indicated that a thunderstorm had earlier occurred from 1800-1856 UTC, and heavy rain showers had occurred from 1811-1951 UTC.

GOES-18 Infrared image at 2058 UTC on 24 January, with a cursor sample of the 2058 UTC Pago Pago (NSTU) METAR surface report [click to enlarge]

________________________

Decoded surface reports from Pago Pago, with the precipitation reports for 24 January (local time) highlighted by a green box [click to enlarge]

Pago Pago recorded 2.76″ of rainfall during their calendar day of 24 January (above) — with most of that occurring during the ~2 hour period from 1811-1951 UTC (below). WSO Pago Pago issued Flash Flood Warnings at 1812 UTC and 2100 UTC on 24 January.

Pago Pago METAR reports, with the period of heavy rain showers (+SHRA) occurring within the red box [click to enlarge]

Categories: GLM, GOES-18, Heavy rain / flooding, Lightning