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1-minute GOES-18 imagery to monitor ongoing heavy rainfall in American Samoa

By Scott Bachmeier •

1-minute GOES-18 Clean Infrared Window (10.3 µm) images, from 1000 UTC to 1600 UTC on 16 December [click to play animated GIF | MP4]

As discussed in this blog post, heavy rainfall had been occurring across the Samoan Islands on 14 December 2023. The South Pacific Convergence Zone (SPCZ) remained in the vicinity of the Samoan Islands on 16 December (surface analyses) — and 1-minute Mesoscale Domain Sector GOES-18 (GOES-West) Infrared images (above) showed another round of deep convection that produced heavy rainfall over the island of Tutuila, which resulted in flash flooding, rockslides/landslides and wind damage (Local Storm Reports). In addition, the 1326 UTC Pago Pago (NSTU) METAR indicated that a brief thunderstorm (TS) developed (below), which ended 18 minutes later at 1344 UTC.

GOES-18 Clean Infrared Window (10.3 µm) image at 1326 UTC on 16 December, with a cursor sample of the corresponding NSTU METAR [click to enlarge]

The GOES-18 Infrared image at 1250 UTC (below) included a cursor sample of the 10.3 µm brightness temperature (white) and Level 2 Rain Rate derived product (green) just west of Tutuila — the Rain Rate was 3.85 in/hr, highlighting the heavy rain potential of these convective showers and thunderstorms. As of 1800 UTC (7 AM local time) on 16 December, Pago Pago had received 3.93 inches of rain in a 6-hour period (text | graph); a total of 4.04 inches of rain was recorded for the calendar day on 16 December (adding to the 3.46 inches on 13 December and 3.59 inches on 14 December). In addition, note that the southeast wind at Pago Pago was gusting to 40 knots (46 mph) at that time — and a heavy rain shower was reducing the surface visibility to 1/4 mile.

GOES-18 Clean Infrared Window (10.3 µm) image at 1250 UTC on 16 December, with a cursor sample of 10.3 µm brightness temperature and Rain Rate derived product just west of Tutuila [click to enlarge]

AWIPS Users: a variety of GOES RGB types combined with Level 2 Derived Product Readouts is available under the “Satellite -> Local Menu Items” menu (below). In the above example, the VIS/IR Sandwich Combo RGB was used to display the Rain Rate — with the RGB components (and the other L2 derived products) subsequently unloaded, to just display the 10.3 µm Infrared imagery along with the Rain Rate.

GOES RGBs with Level 2 Derived Product Readouts menu structure [click to enlarge]


Plot of NSTU rawinsonde data at 1200 UTC on 16 December [click to enlarge]

It bears mention that the Total Precipitable Water value derived from NSTU rawinsonde data at 1200 UTC on 16 December was 2.87 inches (above) — which was a record maximum value for that date/time, according to this SPC site (below).

Climatology of Total Precipitable Water for NSTU rawinsonde reports at 12 UTC [click to enlarge]

MIMIC TPW images covering the 4-day period from 13-16 December (below) showed the SPCZ stream of moisture as it edged southwestward to spend more time streaming across American Samoa.

MIMIC TPW images, from 0000 UTC on 13 December to 2300 UTC on 16 December [click to play animated GIF | MP4]

Categories: GOES-18, Heavy rain / flooding, Level 2 Product Readouts, Microwave