![](\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/images\/2025\/09\/250921_himawari9_infrared_Ragasa_anim.gif\")
<\/a>2.5-minute Himawari-9 Infrared images, from 0002-2042 UTC on 21 September [click to play animated GIF | MP4<\/strong><\/a>]<\/p><\/div>2.5-minute Target Sector JMA<\/strong><\/a> Himawari-9 Infrared images (above)<\/strong><\/em> showed Ragasa as it intensified from a Category 4 Typhoon at 0000 UTC on 21 September 2025 to a Category 5 (140-knot) Super Typhoon at 0600 UTC and then further to a 145-knot Super Typhoon by 1200 UTC (SATCON<\/strong><\/a>). There was a ~2 hour gap in Target Sector images, from 1100-1250 UTC; during that period, 10-minute Full Disk imagery was used to fill the gap.<\/p>\n The primary environmental factor that favored this intensification was low values of deep-layer wind shear<\/strong><\/a> (below)<\/strong><\/em> — in addition, Ragasa traversed a lobe of slightly warmer waters (Sea Surface Temperature<\/strong><\/a> | Ocean Heat Content<\/strong><\/a>) as it reached Category 5 intensity.<\/p>\n Himawari-9 Infrared images, with contours and streamlines of deep-layer wind shear at 1800 UTC on 21 September<\/p><\/div>\n Ragasa was undergoing an eyewall replacement cycle (ERC) on 21 September, which was evident in the MIMIC-TC<\/strong><\/a> product (below)<\/strong><\/em> — the smaller-diameter inner eyewall was eventually replaced by a larger-diameter outer eyewall. However, the ERC did not adversely affect the intensity of the Super Typhoon during the course of the day.<\/p>\n MIMIC-TC product on 21 September<\/p><\/div>\n 3 snapshots of microwave imagery during the day (from DMSP\/SSMIS and NOAA-21\/ATMS) are shown below.<\/p>\n DMSP-16 SSMIS image at 1003 UTC on 21 September<\/p><\/div>\n NOAA-21 ATMS image at 1731 UTC on 21 September<\/p><\/div>\n DMSP-17 SSMIS image at 2152 UTC on 21 September<\/p><\/div>\n [the wind shear, sea surface temperature, ocean heat content and microwave products shown above were sourced from the CIMSS Tropical Cyclones<\/strong><\/a> site]<\/p>\n An RCM-3 Synthetic Aperture Radar (SAR) Wind Speed image (below)<\/strong><\/em> also highlighted a narrow “moat” of lower wind speed that was surrounding the inner eyewall at 2131 UTC (a “brightness temperature moat” feature was also seen in the 2152 UTC DMSP-17 SSMIS microwave image).<\/p>\n RCM-3 Synthetic Aperture Radar image at 2131 UTC on 21 September [click to enlarge]<\/p><\/div>A sunrise-to-sunset animation of 2.5-minute Himawari-9 Visible images (below)<\/strong><\/em> revealed the presence of low-level mesovortices within the large eye. Super Typhoon Ragasa made its first landfall on the tiny island of Babuyan<\/strong><\/a> in the Luzon Strait after 0300 UTC on 22 September.<\/p>\n 2.5-minute Himawari-9 Visible images, from 2152 UTC on 21 September to 0832 UTC on 22 September [click to play animated GIF | MP4<\/strong><\/a>]<\/p><\/div>A Suomi-NPP VIIRS Day\/Night Band image at 0511 UTC on 22 September — when Ragasa was still at Category 5 intensity (below)<\/strong><\/em> displayed the 40-mile diameter eye as its western edge was near Synoptic Station 981330 (Calayan Island<\/strong><\/a>).<\/p>\n Suomi-NPP VIIRS Day\/Night Band image valid at 0511 UTC on 22 September [click to enlarge]<\/p><\/div>\n Sentinel-3B Altimetry data, showing a Significant Wave Height value of 27.75 ft east of Luzon at 0129 UTC on 21 September<\/p><\/div>\n The strong winds associated with Super Typhoon Ragasa caused high waves (above)<\/strong><\/em>, which resulted in an upwelling of cooler sub-surface water in the northwest Philippine Sea — late in the day on 22 September (when Ragasa was located far to west, in the South China Sea), note the pocket of 27-28\u00baC Sea Surface Temperatures (yellow to light orange) along and north of the track of Ragasa at the point where it first reached Category 5 intensity from 0600-1200 UTC on 21 September (below)<\/strong><\/em>. Sea Surface Temperatures over that area of upwelling were around 30\u00baC<\/strong><\/a> just prior to the passage of Ragasa.<\/p>\n Sea Surface Temperature analysis at 2233 UTC on 22 September, with a plot of Ragasa’s track from 18-23 September<\/p><\/div>\n As Ragasa was beginning to move west-northwestward away from northern Luzon on 22 September, a Significant Wave Height of 58.26 ft was sensed at 1352 UTC (below)<\/strong><\/em>.<\/p>\n<\/a><\/a><\/a>