2.5-minute interval rapid-scan Himawari-8 Infrared Window (10.4 µm) images (below) showed the formation of a well-defined eye with an annular storm structure early in the day on 07 July. The eye became less organized as Nepartak approached the island of Taiwan and made landfall as a Category 4 typhoon around 2150 UTC.Surface observations (plot | text) from Feng Nin airport (station identifier RCFN) in Taitung City showed sustained winds of 70 knots (81 mph) with a gust to 99 knots (114 mph) from the north-northeast at 21 UTC, and a pressure of 964.0 hPa (27.47″). iCyclone chaser Josh Morgerman recorded a minimum pressure of 957.7 hPa at 2043 UTC (4:43 am local time) in Taitung City:
— Josh Morgerman (@iCyclone) July 10, 2016
Shortly before landfall, a comparison of DMSP-18 SSMIS Microwave (85 GHz) and Himawari-8 Infrared Window (10.4 µm) images around 20 UTC (below) showed that the eye was still rather distinct on the microwave image. However, the MIMIC-TC product (below) revealed how quickly the eyewall structure eroded once the circulation of Nepartak encountered the rugged terrain of Taiwan. Looking back to earlier periods in the storm history, a 2-panel comparison of Himawari-8 Visible (0.64 µm) and Infrared Window (10.4 µm) images from 06-07 July (below) revealed the presence of mesovortices within the eye on the visible imagery. The spatial resolution of these Visible (0.5 km) and Infrared (2 km) AHI images is identical to what will be provided by the ABI instrument on GOES-R. A Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image from 07 July (viewed using RealEarth) is shown below; the actual satellite overpass time for this image was around 0444 UTC. During the period of rapid intensification on 06 July, 2.5-minute interval rapid-scan Himawari-8 Infrared Window (10.4 µm) images (below) revealed pulses of storm-top gravity waves which were propagating radially outward away from the eye of Nepartak (especially evident during the later half of the animation period). It is also interesting to note that nighttime mesospheric gravity waves could be seen propagating away from the eye/eyewall region of Nepartak at 1729 UTC or 1:29 am local time on a 06 July Suomi NPP VIIRS Day/Night Band (0.7 µm) image (below, courtesy of William Straka, SSEC). Since very little illumination was provided by the Moon (which was in the Waxing Crescent phase, at only 5% of Full), these waves were being illuminated by airglow. The MIMIC-TC product (below) also showed that Nepartak completed an eyewall replacement cycle on 06 July. Animations of 10-minute interval Himawari-8 Infrared Window (10.4 µm) images spanning nearly the entire life cycle of Nepartak — from a tropical depression south of Guam on 03 July to landfall over mainland China on 08 July — are available as an MP4 movie (139 Mbytes) or an animated GIF (493 Mbytes).