{"id":65250,"date":"2025-06-08T08:54:00","date_gmt":"2025-06-08T08:54:00","guid":{"rendered":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/?p=65250"},"modified":"2025-06-12T17:43:40","modified_gmt":"2025-06-12T17:43:40","slug":"anticipating-rain-development-over-tutuila-american-samoa","status":"publish","type":"post","link":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/archives\/65250","title":{"rendered":"Anticipating rain development over Tutuila, American Samoa"},"content":{"rendered":"\n<figure class=\"wp-block-video\"><video height=\"778\" style=\"aspect-ratio: 1256 \/ 778;\" width=\"1256\" controls loop src=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/goeswest_abi_radf_true_color_night_s20250607230023_e20250608094023_f65.mp4\"><\/video><figcaption class=\"wp-element-caption\">GOES-18 True Color imagery (daytime) and Night Microphysics RGB (nighttime), 2300 UTC 7 June &#8211; 0940 UTC 8 June 2025 <\/figcaption><\/figure>\n\n\n\n<p>GOES-18 imagery from the <a href=\"https:\/\/geosphere.ssec.wisc.edu\/#coordinate:-3312901,-1511316;zoom:6;satellite:goeswest;num_frames:65;start_time:2025-06-07T23:00:23Z;timeframe:Start%20Time;\">CSPP Geosphere site<\/a>, above, shows a thin line of trade wind cumulus from which strong convection develops over Tutuila (the main island of American Samoa). The heavy rains prompted the <a href=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/FloodAdvisory_Pago_Late7June2025.png\">issuance of Flood Advisories<\/a>.  What products or imagery might have helped in anticipating this convective development?<\/p>\n\n\n\n<p>LightningCast probabilities between 0000 and 0100 UTC on 8 June, below, computed using <a href=\"https:\/\/cimss.ssec.wisc.edu\/csppgeo\/lightningcast.html\">this CSPP Geo software<\/a>, show small probabilities developing by 0100 UTC.  A forecaster viewing these fields might see them and conclude that something bigger is about to commence.<\/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\/06\/LC_GOES-18_FullDisk_20250608-0000_to_0100_DCCstep.gif\"><img loading=\"lazy\" decoding=\"async\" width=\"1064\" height=\"1038\" src=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/LC_GOES-18_FullDisk_20250608-0000_to_0100_DCCstep.gif\" alt=\"\" class=\"wp-image-65254\"\/><\/a><figcaption class=\"wp-element-caption\">LightningCast Probabilities centered over Samoa, 0000-0100 UTC on 8 June 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n<p>The Clean Window infrared imagery below, from 0040 &#8211; 0110 UTC on 8 June 2025, shows the development of the convection at the western tip of Tutuila.  Cooler brightness temperatures are apparent at 0050 UTC &#8212; that an the increase in LightningCast probability (shown above) might be enough to convince a forecaster that convection is starting.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1141\" height=\"849\" src=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/G18Band13-20250608_0040_0100_0110step.gif\" alt=\"\" class=\"wp-image-65268\"\/><figcaption class=\"wp-element-caption\">GOES-18 Clean Window infrared (Band 13, 10.3 \u00b5m) imagery, 0040-0110 UTC 8 June 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p>GOES-18 Lifted Index fields, a field that is computed in clear skies only, shows an atmosphere slowly destabilizing around Tutuila from 2300 on the 7th to 0210 on the 8th, changing from about -1.1 to -1.7. So &#8212; the cumulus line is approaching an area that is becoming less stable. Strong convection has developed by 0200 UTC. <\/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\/06\/G18DSILiftedIndex-20250607_2300_to_0608_0210anim.gif\"><img loading=\"lazy\" decoding=\"async\" width=\"1141\" height=\"849\" src=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/G18DSILiftedIndex-20250607_2300_to_0608_0210anim.gif\" alt=\"\" class=\"wp-image-65258\"\/><\/a><figcaption class=\"wp-element-caption\">Derived Lifted Index (in clear skies, scaled from -3 to 5) plotted over GOES-18 Clean Window infrared (Band 13, 10.3 \u00b5m) imagery, 2300 UTC 7 June 2025 to 0210 UTC 8 June 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n<p>It&#8217;s worth mentioning that <a href=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/archives\/217\">parallax<\/a> errors from GOES-18, overhead at 137.2<sup>o<\/sup>W (compared to 171<sup>o<\/sup>W for Pago Pago) means that the convection that is mapped to the west of Tutuila is, in reality, over the island. Parallax computations (<a href=\"https:\/\/cimss.ssec.wisc.edu\/goes\/webapps\/parallax\/goes18_asamoa.html\">link<\/a>) suggest that a 30000-foot storm top would be displaced by almost 9 km, or about 4 pixels. The convection was also developing in a region with a bit more moisture (as diagnosed by GOES-R Total Precipitable Water, TPW, below).  Regions just east of Tutuila become more moist over the course of the animation below;  TPW increases from about 1.8&#8243; to 2&#8243;<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1141\" height=\"849\" src=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/G18_TPW-20250607_2300_to_0608_0750anim.gif\" alt=\"\" class=\"wp-image-65261\"\/><figcaption class=\"wp-element-caption\">Derived Total Precipitable Water (in clear skies, scaled from -3 to 5) plotted over GOES-18 Clean Window infrared (Band 13, 10.3 \u00b5m) imagery, 2300 UTC 7 June 2025 to 0750 UTC 8 June 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n<p>The Pago Pago sounding from 0000 UTC on 8 June 2025, below, shows abundant instability available if a modest capping inversion can be broken.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><a href=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/UpperAirPago_08June2025_0000UTC_91765.png\"><img loading=\"lazy\" decoding=\"async\" width=\"837\" height=\"651\" src=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/UpperAirPago_08June2025_0000UTC_91765.png\" alt=\"\" class=\"wp-image-65262\" srcset=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/UpperAirPago_08June2025_0000UTC_91765.png 837w, https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/UpperAirPago_08June2025_0000UTC_91765-300x233.png 300w, https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/UpperAirPago_08June2025_0000UTC_91765-768x597.png 768w\" sizes=\"auto, (max-width: 837px) 100vw, 837px\" \/><\/a><figcaption class=\"wp-element-caption\">Upper Air sounding, 91765\/Pago Pago, American Samoa, 0000 UTC on 8 June 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n<p>Thanks to WSO Pago Pago for alerting me to this challenging case.  The interpretation of the Lifted Index is very much simpler because the colorbar bounds were changed!  Change defaults to highlight subtle features. <\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p>Given that the narrow lines of tradewind cumulus are possible regions of convective development, what tools are available to monitor them at night?  The Day Night Band on NOAA-20\/NOAA-21\/Suomi-NPP produces visible imagery at night.  The image below, from the <a href=\"https:\/\/worldview.earthdata.nasa.gov\/?v=-175.45238971958676,-16.117345491587816,-169.06492260360662,-12.481002119854542&amp;l=Reference_Labels_15m(hidden),Reference_Features_15m(hidden),Coastlines_15m,OrbitTracks_NOAA-20_Descending,VIIRS_SNPP_DayNightBand_At_Sensor_Radiance(hidden),VIIRS_NOAA20_DayNightBand_At_Sensor_Radiance,VIIRS_NOAA21_CorrectedReflectance_TrueColor(hidden),VIIRS_NOAA20_CorrectedReflectance_TrueColor(hidden),VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor(hidden)&amp;lg=true&amp;t=2025-06-08-T13%3A33%3A18Z\">NASA Worldview site<\/a>, shows a narrow line of tradewind cumulus approaching the Samoan Islands and the convection from earlier moving north of the islands.  June 8th was <a href=\"https:\/\/www.moongiant.com\/phase\/6\/08\/2025\/\">two days before a full Moon<\/a>, so there was ample illumination.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"584\" src=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/NOAA-20DayNightBand_1255UTC_08June2025-1024x584.jpg\" alt=\"\" class=\"wp-image-65275\" srcset=\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/NOAA-20DayNightBand_1255UTC_08June2025-1024x584.jpg 1024w, https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/NOAA-20DayNightBand_1255UTC_08June2025-300x171.jpg 300w, https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/NOAA-20DayNightBand_1255UTC_08June2025-768x438.jpg 768w, https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/NOAA-20DayNightBand_1255UTC_08June2025-1536x876.jpg 1536w, https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2025\/06\/NOAA-20DayNightBand_1255UTC_08June2025-2048x1167.jpg 2048w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><figcaption class=\"wp-element-caption\">Day Night Band visible (0.7 \u00b5m) imagery from NOAA-20, 1255 UTC on 8 June 2025;  the orbital path of NOAA-20 and time overhead is indicated at the western edge of the image (Click to enlarge)<\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"<p>GOES-18 imagery from the CSPP Geosphere site, above, shows a thin line of trade wind cumulus from which strong convection develops over Tutuila (the main island of American Samoa). The heavy rains prompted the issuance of Flood Advisories. What products or imagery might have helped in anticipating this convective development? LightningCast probabilities between 0000 and [&hellip;]<\/p>\n","protected":false},"author":19,"featured_media":65264,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[114,115,78],"tags":[],"class_list":["post-65250","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-goes-18","category-lightningcast","category-noaa-20"],"acf":[],"_links":{"self":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/65250","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=65250"}],"version-history":[{"count":11,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/65250\/revisions"}],"predecessor-version":[{"id":65278,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/65250\/revisions\/65278"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/media\/65264"}],"wp:attachment":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/media?parent=65250"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/categories?post=65250"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/tags?post=65250"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}