The RCM-1 (Radarsat Constellation Mission 1) satellite overflew STY Bolaven at 0840 UTC on 11 October. The Himawari-9 infrared (10.4 µm) presentation of the storm is excellent with a symmetric storm, distinct eye, and vigorous outer band convection. SAR winds show the strongest convection in the eastern half of the eyewall, where winds of 80 m/s (> 150 knots) are measured. (This website contains views of Bolaven from multiple SAR overpasses) The structure of the SAR winds (here‘s a zoomed-in view) shows a band of weaker winds outside the strongest winds on the east side of the storm. Is an eyewall replacement cycle occurring?

The SSEC/CIMSS Tropical Weather website includes a section on Microwave-based Probabilities of an Eyewall Replacement Cycle (M-PERC). The diagram below (click on it to see the entire figure including column headers) shows probabilities reached a maximum after 0300 on 11 October.

The MIMIC-TC animation below, however, shows winds consistently at/above 145 knots in the latter part of the animation, and no obvious signature of an ongoing eyewall replacement.

For more information on this storm, refer to the webpages of the Joint Typhoon Warning Center, the RSMC in Tokyo and the CIMSS Tropical Website. Bolaven is forecast to remain at sea as it recurves to the north and east. It is forecast to become a significant mid-latitude extra-tropical cyclone in the Gulf of Alaska by 18 October.

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Target Sector (2.5-minute interval) JMA Himawari-9 AHI Red Visible (0.64 µm) images (above) and Clean Infrared Window (10.4 µm) mages (below) showed Super Typhoon Bolaven as it reached Category 5 intensity west of the Northern Mariana Islands at 0000 UTC (SATCON) on 11 October 2023. Bolaven was an annular tropical cyclone, exhibiting a symmetric eye surrounded by a broad ring of dense and cold deep convection.

A closer view of Himawari-9 Visible and Infrared mages (below) revealed mesovortices within the eye, as well as the distinct stadium effect of the eye (with its edges sloping outward with height).

Microwave (85 GHz) images from DMSP-16 (at 0818 UTC) and AMSR2 (at 1627 UTC) from the CIMSS Tropical Cyclones site (below) displayed a compact and fully closed eyewall.

A noctrnal Suomi-NPP VIIRS Day/Night Band (0.7 µm) image valid at 1647 UTC (below) showed a pronounced packet of mesospheric airglow waves (reference) propagating southward away from the eye of Bolaven.

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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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