GOES-18 (GOES-West) SO2 RGB and Ash RGB images (above) showed the complex transport of a volcanic cloud (shades of yellow in the SO2 RGB imagery) produced by an explosive eruption of Mount Shishaldin that began around 1340 UTC on 25 September 2023. The bulk of the cloud drifted to the southeast, while another part wrapped cyclonically across the far southeastern Bering Sea. There was also a small secondary eruption that began around 1610 UTC, sending a small volcanic cloud eastward (that moved just north of False Pass).

There were trace to minor amounts of volcanic ashfall reported in False Pass, King Cove, Cold Bay and Sand Point, occurring in conjunction with light rainfall. A 1912 UTC Pilot Report (PIREP) issued at Sand Point (below) mentioned that volcanic ash (VA) was falling in light rain (-RA), covering surfaces.

A radiometrically retrieved Volcanic Ash Height product from the NOAA/CIMSS Volcanic Cloud Monitoring site (below) indicated that parts of the volcanic cloud reached heights in the 18-20 km range.

In Nighttime Microphysics RGB  + daytime True Color RGB images from the CSPPGeoSphere site (below), after sunrise the leading edge of the southeast-moving volcanic cloud exhibited shades of tan to light brown (indicating significant ash content).

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Wave observations from the Aunu’u site just to the east of American Samoa, above, show waves exceeding 12 feet starting late in the day on 22 September and persisting through the weekend into the 25th. The National Weather Service office in Pago Pago issued High Surf Warnings during this event

ASZ001>004-251915-Tutuila-Aunuu-Manua-Swains Island-Rose Atoll-705 PM SST Sun Sep 24 2023

...HIGH SURF WARNING NOW IN EFFECT UNTIL MONDAY...

WHAT...Surf of 15 to 18 feet

WHERE...East and south shores

WHEN...Through Monday

IMPACTS...Expect ocean water occasionally sweeping across beaches,very strong breaking waves, and strong longshore and potentially deadly rip currents. Some strong coastal erosion is likely. Very large waves may bring some ocean debris onto roadways, impact small harbors, and make navigating the harbor channel dangerous.

PRECAUTIONARY/PREPAREDNESS ACTIONS...Residents in vulnerable locations may experience flooding. Some roads in vulnerable, low-lying areas may be closed from floodwaters. Stay tuned to local officials for any road closures or evacuations. Anyone in low-lying and vulnerable areas could be swept out to sea and face significant injury or death.

MetopB and MetopC Advanced Scatterometer plots (taken from this website), below, show a large region of strong (20-25 knot) east-southeast winds to the west and south of Samoa and American Samoa.

GOES-18 Derived Motion Wind vectors, below, similarly show a large region of 20-25 knot winds to the east and south of the Samoan Islands. These winds are helping to force the wave action.

Altimetry from satellites can also be used to determine wave heights, and a plot (also from this website, then click on ‘Altimeter’) is shown below. It is difficult to compare these values to the buoy values above; altimetry plots show the Significant Wave Height, namely the mean wave height of the highest 1/3 of all waves. The single swath shown below has Significant Wave Heights between 9 and 11 feet, at 1343 UTC on 23 September 2023.

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) showed Ophelia for a few hours after it became a Tropical Storm at 1800 UTC on 22 September 2023. The low-level circulation center (LLCC) was initially exposed, but deep convection just to the west began to increase in coverage and intensity as it wrapped around and soon obscured the LLCC. Ophelia was becoming better organized as it traversed the warm water (Sea Surface Temperature | Ocean Heat Content) of the Gulf Stream.

1-minute GOES-16 Infrared images with/without an overlay of GLM Flash Extent Density (below) indicated that lightning activity began to increase around 1900 UTC, as smaller-scale pulses of embedded convection started to exhibit cloud-top infrared brightness temperatures around -70ºC. A notable lightning jump was evident from 1925-1945 UTC.

A closer look at the aforementioned lightning jump is shown below, using 5-minute GOES-16 Infrared images and GLM Flash Extent Density — a brief pulse of convection with cold overshooting tops (brightness temperatures around -70ºC, brighter shades of white embedded within darker black regions) occurred from 1916-1931 UTC, with the Flash Extent Density then ramping up from 1926-1946 UTC (reaching a peak at 1936 UTC).

In comparisons of GOES-16 Infrared (10.3 µm), CLAVR-x Cloud Top Height (CTH) and Operational CTH derived products at 1921 UTC (above) and 1926 UTC (below), it can be seen that the CIMSS-derived CLAVR-x CTH (having a 2-km resolution) was far superior to the Operational CTH (having a 10-km resolution, as is currently available in AWIPS) in terms of determining both the areal coverage and the magnitude of cloud heights associated with the cold overshooting tops that immediately preceded the lightning jump. In fact, at 1926 UTC, the CLAVR-x CTH value was nearly 10 kft higher than the Operational CTH (57384 ft vs 47687 ft).

Several hours later, a closer look at 1-minute GOES-16 Infrared images with/without an overlay of GLM Flash Extent Density (below) showed Ophelia approaching the coast of North Carolina, making landfall at 1020 UTC or 6:20 AM EDT on 23 September (producing strong winds and heavy rainfall). The center of Ophelia passed between Buoy 41037 to the southwest (which recorded a peak wind gust of 72 knots) and Buoy CLKN7 to the northeast (which recorded a peak wind gust of 67 knots).

Hourly MIMIC Total Precipitable Water images (below) depicted the tropical moisture that was transported inland across the Mid-Atlantic states, resulting in heavy rainfall and flooding.

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10-minute Full Disk sector GOES-18 (GOES-West) Day Land Cloud Fire RGB, Shortwave Infrared (3.9 µm), “Clean” Infrared Window (10.3 µm) and “Red” Visible (0.64 µm) + Fire Power derived product (a component of the GOES Fire Detection and Characterization Algorithm FDCA) images (above) showed signatures of multiple wildfires across northeastern British Columbia (BC) and northwestern Alberta (AB), some of which produced numerous  pyrocumulonimbus (pyroCb) clouds late in the day on 22 September 2023. Several of these fires burned very hot, exhibiting 3.9 µm shortwave infrared brightness temperatures of 137.88ºC (the saturation temperature of GOES-18 ABI Band 7 detectors) — and for the large wildfire near Rainbow Lake AB (CWSH), Fire Power values intermittently reached the 6400-6405 MW range (which are the highest GOES Fire Power values sampled by this author for any wildfire).

True Color RGB images from the CSPP GeoSphere site (below) displayed the BC/AB pyroCb development, as well as widespread dense smoke from the many wildfires across the region.

A longer animation of GOES-18 Infrared images covering a larger area (below) showed that while two of the largest BC fires produced 1 to 4 pyroCb clouds each — pyroCb clouds are defined as having cloud-top 10.3 µm infrared brightness temperatures of -40ºC and colder, shades of blue — one of the two largest AB fires produced an amazing string of 7 pyroCb clouds (between 2300 UTC on 22 September and 0800 UTC on 23 September). About 100 miles downstream (northeast) of that prolific pyroCb-producing AB wildfire, smoke reduced the surface visibility to 1/2 mile for several hours at Hay River (CYHY) in the Northwest Territories.

The coldest cloud-top 10.3 µm infrared brightness temperature exhibited by the largest of the AB pyroCbs was -60.6ºC — placing it at an altitude near 12 km (just below the tropopause) as seen in a plot of rawinsonde data from Fort Nelson BC (CYYE) (below).

On the following day, the leading edge of high-altitude BC/AB pyroCB smoke plumes could be seen moving southeastward across Hudson Bay in True Color RGB images from both GOES-18/GOES-West (above) and GOES-16/GOES-East (below).

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