JMA Himawari-9 Clean Infrared Window (10.4 µm) images, from 2012 UTC on 09 October to 0752 UTC on 10 October [click to play animated GIF | MP4]

Target Sector (2.5-minute interval) JMA Himawari-9 AHI Clean Infrared Window (10.4 µm) images (above) and Red Visible (0.64 ) 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).

JMA Himawari-9 Red Visible (0.64 µm) images, from 2012 UTC on 09 October to 0752 UTC on 10 October [click to play animated GIF | MP4]

JMA Himawari-9 Red Visible (0.64 µm) and Clean Infrared Window (10.4 µm) images at 0322 UTC on 10 October [click to enlarge]

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 rawinsonde data from Guam (below).

Plot of rawinsonde data from Guam at 000 UTC on 10 October [click to enlarge]

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.

JMA Himawari9 Infrared Window (11.2 µm) images, with an overlay of deep-layer wind shear at 0000 UTC [click to enlarge]

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