GOES-18 (GOES-West) Dust RGB images (above) showed a plume of resuspended volcanic ash (brighter shades of pink) from the 1912 Novarupta-Katmai eruption in Alaska, which was being transported offshore across the Shelikof Strait (and Buoy 46077, where the peak wind gusts were 31 knots) toward Kodiak Island on 10 October 2023. Surface ash within the Valley Of Ten Thousand Smokes was being lofted by a burst of strong northwesterly winds — a toggle between the 1200 UTC Dust RGB image and Topography (below) highlighted the valleys associated with the ash source region.

As the plume of resuspended ash moved over the northern portion of Kodiak Island, the Kodiak Airport (PADQ) began to report Volcanic Ash (VA) at 1900 UTC (below) — and the ash plume briefly restricted the surface visibility to 8 miles at 2200 UTC.

While a signature of the plume was also evident in GOES-18 Ash RGB imagery, it was more obvious in the Dust RGB (below) — both RGBs use the same spectral bands and spectral band differences, but the individual RGB components are scaled differently (so an examination of both is advised, in order to determine which RGB is best to track an ash-related feature).

GOES-18 daytime True Color RGB + Nighttime Microphysics RGB images from the CSPP GeoSphere site (below) provided another view of the resuspended ash plume.

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The direct broadcast antenna at the NWS forecast office on Guam processed important information to show details of Typhoon Bolaven as it passed through the Marianas Islands on 10 October. The toggle above compares VIIRS band M07 (0.865 ) and Rain Rate derived from ATMS imagery at 0338 UTC, when the typhoon was east of Guam. It passed between Rota and Tinian just after 0900 UTC, based on this graphic from the Joint Typhoon Warning Center. The storm at the time was moving through a region of low shear (shear image from the SSEC/CIMSS Tropical Weather Website).

GCOM-W1 overflew Guam shortly before NOAA-20. The 89-GHz image from that overpass is shown below. THis image in combination with the rain rate image above might convince you that Bolaven at this time was storm with an asymmetric distribution of precipitation, with much of the precipitation in the western quadrant of the storm.

CSPP software includes GAASP software used to compute winds, and the derived windspeeds from the AMSR-2 observations are shown below (in a display rendered by Panoply). The strongest winds are in the western half of the storm.

At present, Bolaven is strengthening as it pulls away from the Marianas. For more information on the storm, consult the CIMSS Tropical Website, the JTWC website and the RSMC in Tokyo. Thanks to Doug Schumacher, CIMSS, for slacking me these images!

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Himawari-9 is, of course, staring at Guam. The 4 Target sector images below show Band 4 (0.86 µm) from 0332-0339, bracketing the NOAA-20 overpass. The combination of geostationary satellites and polar orbiting satellites allows a user to access the strengths of both.

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Bolaven underwent a remarkable transformation subsequent to its passage through the Marianas, as shown below. By 1932 UTC, a distinct eye is apparent! The 2100 UTC advisory from JTWC reports a storm with 100-knot winds, up from 70 knots at 0600 UTC!

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Target Sector (2.5-minute interval) JMA Himawari-9 AHI Clean Infrared Window (10.4 µm) images (above) and Red Visible (0.64 µm) mages (below) showed Tropical Storm Bolaven as it intensified to become a Category 1 Typhoon just southeast of the Mariana Islands at 0000 UTC (SATCON | JTWC advisory) on 10 October 2023. The coldest cloud-top infrared brightness temperatures, associated with brief vortical hot towers within the Central Dense Overcast of Bolaven, were around -90ºC (yellow pixels embedded within dark purple areas).

One of the more notable vortical hot towers (VHTs) occurred just southeast of the island of Rota at 0322 UTC on 10 October, as seen in a toggle between Himawari-9 Red Visible (0.64 µm) and Clean Infrared Window (10.4 µm) images (above). The coldest infrared brightness temperature within the VHT cluster of yellow pixels was -94ºC; that temperature represented a significant air parcel overshoot of the local tropopause — which was -81.9ºC at 106 hPa, as seen in a plot of 0000 UTC rawinsonde data from Guam (below). On a side note, the Total Precipitable Water (PW) value of 2.74 in analyzed from that sounding was a record high value for 0000 UTC soundings on 10 October (the previous record was 2.61 in).

Himawari-9 Infrared Window (11.2 µm) images from the CIMSS Tropical Cyclones site (below) showed that Bolaven was moving through an environment of low deep-layer wind shear — which, in addition to its motion across warm water (SST | OHC), favored continued intensification.

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Former Hurricane Philippe lost tropical characteristics at 1500 UTC on 6 October, as it interacted with extratopical features moving over it from the USA. (Click here for a UW-Madison weather watch on this event with commentary by Profs Jon Martin and Michael Morgan). There are several players of note in this animation: Philippe, a disorganized mass of convection off the east coast of the US, a subtropical jetstream moving through the southern United States and a potent upper-tropospheric impulse moving from Canada into the upper Great Lakes. Each of these systems have potential vorticity anomalies (different shades of orange in the RGB) that can be tracked.

Philippe’s extratropical transition is coincident with the arrival of a PV anomaly associated with the subtropical jet; that anomaly is moving through the mid-Atlantic states late in the day 6 October/early 7 October. Starting on 8 October, the PV anomaly with the system moving through the Great Lakes also affects the poleward-moving remains of Philippe.

The resultant occluded cyclone remained over eastern Canada through 11 October — as seen below in an animation of surface analyses from the Ocean Prediction Center.

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