![\"GOES-17\"](\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/images\/2020\/02\/200216_200218_goes17_infrared_American_Samoa_anim.gif\")
<\/a>GOES-17 “Clean” Infrared Window (10.35 \u00b5m)<\/em> images, 16-18 February [click to play animation | MP4<\/strong><\/a>]<\/p><\/div>GOES-17 (GOES-West)<\/em> “Clean” Infrared Window (10.35 \u00b5m<\/strong><\/a>) images (above)<\/strong><\/em> showed the movement of numerous thunderstorms across American Samoa during the 16-18 February 2020 period. This deep convection was being forced by an active South Pacific Convergence Zone<\/strong><\/a> or “Monsoon Trough” (surface analysis<\/strong><\/a>) and the presence of Tropical Invest 96P (named TD07F by the Fiji Met Service \/ Nadi Tropical Cyclone Centre<\/strong><\/a>) northwest of Samoa. Due to outflow from a nearby thunderstorm<\/strong><\/a>, winds gusted to 60 knots at Pago Pago, American Samoa (NSTU) at 11 UTC on 17 February<\/strong><\/a>.<\/p>\n With an increasing probability of Invest 96P becoming better organized (aided by low values of deep-layer wind shear<\/strong><\/a> along with modest upper-level divergence<\/strong><\/a>), a GOES-17 Mesoscale Domain Sector<\/strong><\/a> was positioned over the Samoan Islands on 18 February — providing “Red” Visible (0.64 \u00b5m<\/strong><\/a>) and “Clean” Infrared Window images at 1-minute intervals (below)<\/strong><\/em>. During this period, the coldest convective overshooting tops exhibited infrared brightness temperatures in the -80 to -85\u00baC range (which corresponded to the tropopause temperatures seen in Pago Pago rawinsonde data<\/strong><\/a>).<\/p>\n GOES-17 “Red” Visible (0.64 \u00b5m)<\/em> and “Clean” Infrared Window (10.35 \u00b5m)<\/em> images with surface plots for Pago Pago, American Samoa on 18 February [click to play animation | MP4<\/strong><\/a>]<\/p><\/div>\n ===== 20 February Update =====<\/strong><\/p>\n GOES-17 “Red” Visible (0.64 \u00b5m)<\/em> and “Clean” Infrared Window (10.35 \u00b5m)<\/em> images with surface plots for Pago Pago, American Samoa on 20 February [click to play animation | MP4<\/strong><\/a>]<\/p><\/div>Another tropical depression (Invest 97P\/TD09F) developed along the active Monsoon Trough on 20 February (surface analyses<\/strong><\/a>), intensifying just south of American Samoa to become Tropical Cyclone Vicky (TC 17P) as of 18 UTC (JTWC advisory<\/strong><\/a>). Once again a GOES-17 Mesoscale Sector was positioned over the region — “Red” Visible (0.64 \u00b5m) and “Clean” Infrared Window (10.35 \u00b5m) images (above)<\/strong><\/em> showed the gradual organization of Vicky; the coldest cloud-top infrared brightness temperature of convective overshooting tops was -90\u00baC. Surface observations<\/strong><\/a> revealed a wind gust to 65 knots at Pago Pago, American Samoa just before 20 UTC.<\/p>\n GOES-17 Infrared Window (11.2 \u00b5m) images from the CIMSS Tropical Cyclones<\/strong><\/a> site (below)<\/strong> <\/em>showed that Vicky was moving through an environment characterized by of low values of Deep Layer Wind Shear<\/strong><\/a>, a favorable factor for further intensification.<\/p>\n GOES-17 Infrared Window (11.2 \u00b5m)<\/em> images with contours of Deep Layer Wind Shear [click to enlarge]<\/p><\/div>Hourly MIMIC Total Precipitable Water<\/strong><\/a> images during the 16-20 February period (below)<\/strong> <\/em>displayed the northwest-to-southeast oriented band of elevated moisture along the South Pacific Convergence Zone (or Monsoon Trough). The Samoan Islands are centered near 14.3\u00b0 S latitude, 170.1\u00b0 W longitude.<\/p>\n<\/a><\/a><\/a>