{"id":65008,"date":"2025-05-28T15:53:28","date_gmt":"2025-05-28T15:53:28","guid":{"rendered":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/?p=65008"},"modified":"2025-05-28T16:54:09","modified_gmt":"2025-05-28T16:54:09","slug":"heavy-rain-on-american-samoa","status":"publish","type":"post","link":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/archives\/65008","title":{"rendered":"Heavy Rain on American Samoa"},"content":{"rendered":"\n<figure class=\"wp-block-video\"><video height=\"838\" style=\"aspect-ratio: 1472 \/ 838;\" width=\"1472\" controls loop src=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/05\/goeswest_abi_radf_true_color_night_s20250528080020_e20250528145020_f42.mp4\"><\/video><figcaption class=\"wp-element-caption\"> GOES-18 Night Microphysics RGB 0800-1450 UTC on 28 May 2025<\/figcaption><\/figure>\n\n\n\n<p>Heavy rains developed overnight over American Samoa, as depicted by the animation above from the <a href=\"https:\/\/geosphere.ssec.wisc.edu\/#playing:true;coordinate:-3296275,-1523482;zoom:6.6;satellite:goeswest;num_frames:42;frame_rate:5;start_time:2025-05-28T08:00:20Z;timeframe:Start%20Time;\">CSPP Geosphere site<\/a>. Low clouds &#8212; white\/cyan in the RGB &#8212; start to show vertical development (that is, they get more and more red) shortly after 1000 UTC with more vigorous vertical growth apparent after 1100 UTC. Pago Pago on the island of Tutuila has had a particularly wet month: 25&#8243; of rainfall through 27 May, which is the <a href=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/05\/MayPrecipitationXMacis.png\">second wettest May on record there<\/a> (data from <a href=\"https:\/\/xmacis.rcc-acis.org\/\">here<\/a>). What clues were present to help anticipate this convective development? The animation below shows GOES-18 Clean Window infrared (Band 13, 10.3) imagery from 1000-1400 UTC, and it is overlain by GOES-18 estimates of Lifted Index (scaled from -5 to 4). American Samoa is at the northern edge of a pool or greater instability that is available given a suitable trigger.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><a href=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/05\/G18Band13_LI_M5to4-20250528_1000_to_1400step.gif\"><img loading=\"lazy\" decoding=\"async\" width=\"1141\" height=\"849\" src=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/05\/G18Band13_LI_M5to4-20250528_1000_to_1400step.gif\" alt=\"\" class=\"wp-image-65011\"\/><\/a><figcaption class=\"wp-element-caption\">GOES-18 Clean Window Infrared imagery (Band 13, 10.3) and derived Lifted Index, 1000-1400 UTC on 28 May 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n<p>Sometimes, LightningCast probability fields (available <a href=\"https:\/\/cimss.ssec.wisc.edu\/severe_conv\/pltg.html\">here<\/a>) can give a suitable warning of convective development (and, subsequently, lightning) as discussed in <a href=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/archives\/64890\">this blog post<\/a> (and elsewhere):  that is, contours start to appear with convective initiation. Convective development on 28 May was quite rapid. Lightning occurred within about 20 minutes of the first contour appearing just south of Tutuila in the animation below.  In other words, LightningCast in this case was helpful in alerting a forecaster that convection was developing &#8212; but that signal was also apparent in single-banded imagery!  <\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1444\" height=\"820\" src=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/05\/G18LightningCast_1130_to_1300UTC_28May2025_anim.gif\" alt=\"\" class=\"wp-image-65013\"\/><figcaption class=\"wp-element-caption\">LightningCast Probability fields around the Samoan Islands, 1130-1300 UTC on 28 May 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n<p>At 1330 UTC (the middle of the night in American Samoa), a Flash Flood Warning was issued for American Samoa.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"735\" height=\"816\" src=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/05\/WSOPPG_FFWarning_28May2025.png\" alt=\"\" class=\"wp-image-65017\" srcset=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/05\/WSOPPG_FFWarning_28May2025.png 735w, https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/05\/WSOPPG_FFWarning_28May2025-270x300.png 270w\" sizes=\"auto, (max-width: 735px) 100vw, 735px\" \/><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>Heavy rains developed overnight over American Samoa, as depicted by the animation above from the CSPP Geosphere site. Low clouds &#8212; white\/cyan in the RGB &#8212; start to show vertical development (that is, they get more and more red) shortly after 1000 UTC with more vigorous vertical growth apparent after 1100 UTC. Pago Pago on [&hellip;]<\/p>\n","protected":false},"author":19,"featured_media":65015,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[42,114,115],"tags":[],"class_list":["post-65008","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-convective-initiation","category-goes-18","category-lightningcast"],"acf":[],"_links":{"self":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/65008","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/users\/19"}],"replies":[{"embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/comments?post=65008"}],"version-history":[{"count":5,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/65008\/revisions"}],"predecessor-version":[{"id":65019,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/65008\/revisions\/65019"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/media\/65015"}],"wp:attachment":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/media?parent=65008"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/categories?post=65008"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/tags?post=65008"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}