Suomi-NPP VIIRS Day/Night Band (0.7 µm) image valid at 1625 UTC [click to enlarge]

Tropical Storm Bolaven formed at 1200 UTC on 07 October 2023, about 540 miles southeast of Guam (JTWC advisory). With sufficient illumination from the Moon (which was in the Waning Crescent phase, at 41% of Full), a nighttime Suomi-NPP VIIRS Day/Night Band (0.7 µm) image valid at 1625 UTC (above) showed Bolaven as it was centered about 200 miles northeast of Chukk International Airport (METAR identifier PTKK) on Weno Island.

JMA Himawari-9 AHI Infrared Window (11.2 µm) images from the CIMSS Tropical Cyclones site (below) showed that Bolaven was moving through an environment of low to moderate deep-layer wind shear.

JMA Himawari9 Infrared Window (11.2 µm) images, with an overlay of deep-layer wind shear at 1500 UTC [click to enlarge]

A Himawari-9 Infrared / Water Vapor Difference product (reference) (below) highlighted areas of deep convection where overshooting tops were likely penetrating the local tropopause (yellow to red to violet enhancement).

JMA Himawari-9 Infrared / Water Vapor Difference images [click to enlarge]

Bolaven was also traversing very warm warm water, where Sea Surface Temperature and Ocean Heat Content values were rather high (below).

Sea Surface Temperature and Ocean Heat Content [click to enlarge]

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