The animation above shows ProbSevere LightningCast probabilities over the Island of Guam for 80 minutes near noon local time on 6 October 2022 (imagery taken from this RealEarth website). The animation above shows LightningCast probabilities increasing from 0110 UTC (when a 10% contour appears) through 0140 UTC and 0150 UTC (when a 75% contour — in magenta — is present. The sequence of events initially caused some astonishment when the 0110 UTC image appeared. The toggle below compares 0100 and 0110 UTC imagery; there appears to be little difference in the imagery between those two times, yet probabilities increase. It seemed odd at the time that maximum values were separated from the observed clouds!

Lightning was observed at 0141 UTC, just off the east coast of central Guam, and at 0152 UTC, close to the NWS Office in Barrigada (and in fact, that thunder was audible in the office). Both lightning events fell within (or very close to) the 75% contour, and were also close to the radar, so radar interrogation of the storm was difficult.

As noted in the blog title, atmospheric winds during this event were light. Click here to see a toggle of satellite-derived winds at upper levels (above 400 mb) and lower levels (below 400 mb) from the SSEC Tropical Website (direct link to western Pacific winds).

The image below shows the detected lightning (in the Guam Forecast Office AWIPS display system) at 0152 UTC. Click here to view a similar image showing one lightning strike at 0141 UTC.

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Overlapping 1-minute Mesoscale Domain Sectors provided GOES-16 (GOES-East) images at 30-second intervals from all 16 ABI spectral bands (above), which displayed the northeast-moving warm thermal signature of a SpaceX Falcon-9 rocket booster as the Crew-5 Mission was launched from Cape Canaveral Space Force Station in Florida at 16:00:57 UTC on 05 October 2022. The low-altitude rocket launch condensation cloud was also evident, drifting slowly eastward away from the launch site. One or both of these rocket launch signatures were detected in all 16 of the ABI spectral bands.

30-second GOES-16 Plume RGB images (below) provided a multi-band integrated view that highlighted both the northeast-moving hot thermal signature of the rocket booster (lighter shades of green to yellow), and the low-altitude rocket condensation cloud (darker shades of green) that drifted eastward.

In a time-matched comparison of Rocket Plume RGB images from GOES-16 and GOES-17 (GOES-West), valid at 16:02:55 UTC (below), the significant eastward displacement of the brighter yellow rocket thermal signature in the GOES-17 image was due to parallax — resulting from the very large viewing angle from that satellite, especially for such a high-altitude feature (approximately 39 km at that point in time).

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JMA Himawari-8 Visible (0.64 µm) and Infrared Window (10.4 µm) images (above) showed the development of “island-effect” thunderstorms over Guam on 05 October 2022 — as mentioned in the NWS Guam Area Forecast Discussion, these storms produced 2-3 inches of rainfall over parts of western/central Guam (prompting the issuance of a Flood Advisory: Text | Tweet).

This type of island-effect convection occurred because the typical easterly trade wind flow within the  boundary layer was disrupted when a trough of low pressure became situated across the region, which led to a regime of light surface winds across the Mariana Islands (below) — and daytime heating of the islands contributed to “land breeze” convergence which aided convective development.

Hourly images of the MIMIC Total Precipitable Water product, viewed using RealEarth (below), indicated that abundant moisture was in place over Guam and the Mariana Islands during this period — for example, 57.75 mm (2.27 inches) in the vicinity of Guam at 0000 UTC (the Guam rawinsonde TPW value at that time was 54.48 mm or 2.15 inches).

A toggle between Suomi-NPP VIIRS True Color RGB and Infrared Window (11.45 µm) images valid at 0332 UTC (below) showed a thunderstorm that was developing over the western edge of the island.

Another example of island-effect convection over Guam on the following day is discussed here.

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed Hurricane Ian as it made landfall as a Category 1 storm near Georgetown, South Carolina at 1805 UTC on 30 September 2022 — producing wind gusts as high as 92 mph and rainfall totals exceeding 5 inches. The low-level circulation center was mostly obscured by high clouds during the time period shown, though partial clearing did reveal some of the low cloud motions within the southeastern quadrant of the hurricane.

The hurricane center moved just east of Buoy 41004, where a wind gust to 64 knots / 74 mph was recorded several hours prior to the closest passage. The Buoy 41004 sea surface temperature as Ian moved through was 80ºF, with a cooling trend seen during the following 4 days (due to the upwelling of cooler sub-surface water, caused by wind-driven high waves).

GOES-16 Day Cloud Phase Distinction RGB images (below) helped to discriminate between the low-level clouds (shades of cyan) and mid to high-level clouds (shades of green to yellow).

GOES-16 “Clean” Infrared Window (10.3 µm) images (below) showed that the coldest cloud-top infrared brightness temperatures were around -70ºC (darker shades of red).

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