{"id":64627,"date":"2025-05-01T16:42:34","date_gmt":"2025-05-01T16:42:34","guid":{"rendered":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/?p=64627"},"modified":"2025-05-12T16:01:26","modified_gmt":"2025-05-12T16:01:26","slug":"persistent-convection-over-tutuila-american-samoa-late-on-30-april-samoa-standard-time","status":"publish","type":"post","link":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/archives\/64627","title":{"rendered":"Persistent convection over Tutuila, American Samoa late on 30 April Samoa Standard Time"},"content":{"rendered":"\n

GOES-18 imagery\/products, shown below, depict an area of enhanced instability and moisture centered on American Samoa, and convection develops and persists over\/around the main island of American Samoa, Tutuila. The convection appears to form along an east-west line that drifts over the island between 0400 and 0800 UTC.<\/p>\n\n\n\n

\"\"<\/a>
GOES-18 Derived Lifted Index (in clear air, scaled from -5 to 5) and Clean Window infrared (Band 13, 10.3) imagery, 0300 – 0950 UTC on 1 May 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

Total Precipitable Water fields, below, suggest the convection was at the leading edge of a somewhat more moist airmass: TPWs increased from 1.8″ (reddish in the enhancement) to 2.0+” (lilac\/purple in the enhancement) as the convection developed on the leading edge of the enhanced moisture.<\/p>\n\n\n\n

\"\"<\/a>
GOES-18 Derived Total Precipitable Water (in clear air) and Clean Window infrared (Band 13, 10.3) imagery, 0300 – 0950 UTC on 1 May 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

CSPP Geosphere<\/a> visible\/night microphysics RGB imagery, below, (click here<\/a> for a faster animation, also from 0010 – 1210 UTC on 1 May 2025) shows the progression of the convection from low-level clouds to strong showers. The low-level outflow boundaries show up nicely as light blue\/white\/pink arcs that become progressively more dark red as the convection develops.<\/p>\n\n\n\n

GOES-18 Full DIsk imagery, 0010 UTC – 1210 UTC on 1 May 2025<\/figcaption><\/figure>\n\n\n\n

What other products are useful in diagnosing the atmosphere? The SSEC\/CIMSS Tropical Weather page<\/a> includes wind diagnostics over the South Pacific, and they can be retrieved from the data archive at that page. The vorticity analysis from 21 UTC\/30 April 2025 to 120 UTC\/1 May 2025, below, shows an increase in low-level vorticity over Samoa, reflecting the convective development that is occurring there. The center of the vorticity slowly drifts north as well during the animation. The vorticity fields have a structure that is in agreement with the observed convection; however, upper-level divergence and low-level convergence fields (not shown) do not.<\/p>\n\n\n\n

\"\"<\/a>
Diagnosed 850-mb vorticity from 2100 UTC on 30 April through 1200 UTC on 1 May 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

MIMIC Total Precipitable Water fields (source), below, also show the subtle increase in TPW that accompanied the convection over Samoa.<\/p>\n\n\n\n

\"\"<\/a>
Hourly MIMIC Total Precipitable Water fields over the South Pacific, 2000 UTC 30 April – 1200 UTC 1 May 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

Scatterometry data for this event was sparse. The toggle below — images that were taken from the manati website (https:\/\/manati.star.nesdis.noaa.gov\/<\/a>) — shows OSCAT imagery at 1128 UTC and MetopC imagery at 2013 UTC (both on 30 April 2025). There is speed convergence to the southeast of American Samoa.<\/p>\n\n\n\n

\"\"
OSCAT-3 (1128 UTC) and MetopC ASCAT (2013 UTC) scatterometery on 30 April 2025 (Click to enlarge) <\/figcaption><\/figure>\n\n\n\n

LightningCast probabilities (available from an American Samoa Sector at this website<\/a>) shows increasing probabilities from 0300 UTC to 0600 UTC, with GLM lightning observations starting at 0440 UTC.<\/p>\n\n\n\n

\"\"<\/a>
LightningCast probabilities, 0300 – 0600 UTC plotted over GOES-18 clean window infrared imagery, along with GLM observations of Flash Extent Density, 1 May 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

LightningCast probabilities can also be calculated with CSPP Geo software<\/a>, and the output for a longer period is shown below.<\/p>\n\n\n\n

\"\"<\/a>
LightningCast Probability, 0000 – 1000 UTC on 1 May 2025 (Click to enlarge) ; the underlying satellite imagery changes at 0440 UTC, around sunset<\/figcaption><\/figure>\n\n\n\n
\n\n\n\n

NUCAPS profiles can give a good estimate of the thermodynamic state of the atmosphere. Gridded NUCAPS fields, not shown here, are very useful because they show horizontal fields that allow for a quicker diagnostic of thermodynamics than via the tedious clicking of multiple sounding points. These profiles can be compared to the 0000 UTC\/1200 UTC 1 May 2025upper-air sounding from the balloon launched from the Pago Pago airport, shown below. These plots were retrieved from the University of Wyoming sounding site<\/a>.<\/p>\n\n\n\n

\"\"
Upper air sounding at NSTU\/91765 0000 and 1200 UTC 1 May 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

What did the NUCAPS profiles show? NUCAPS Sounding availability at 0008 UTC (NOAA-20) and 0059 UTC (NOAA-21) are shown below.<\/p>\n\n\n\n

\"\"
NUCAPS Sounding Availability at 0008 and 0059 UTC on 1 May 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

The four closest profiles to Tutuila, shown in the animation below, all have similar thermodynamic characteristics. Moisture is more abundant in the easternmost points.<\/p>\n\n\n\n

\"\"
NUCAPS Sounding Availability, and Profiles\/Diagnosed information for the 4 points closest to Tutuila, 0018 UTC on 1 May 2025 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

The information from NOAA-21, at 0058 UTC, below, along a north-south line that passes north-south through the diagnosed maximum in instability, shows CAPE values are greatest just north of the American Samoa islands, and Total Precipitable Water is greatest over the islands.<\/p>\n\n\n\n

\"\"
NUCAPS profiles along a North-South line to the east of Tutuila, as indicated; profiles are at 0108 UTC on 1 May 2025 (Click to enlarge)<\/figcaption><\/figure>\n","protected":false},"excerpt":{"rendered":"

GOES-18 imagery\/products, shown below, depict an area of enhanced instability and moisture centered on American Samoa, and convection develops and persists over\/around the main island of American Samoa, Tutuila. The convection appears to form along an east-west line that drifts over the island between 0400 and 0800 UTC. Total Precipitable Water fields, below, suggest the […]<\/p>\n","protected":false},"author":19,"featured_media":64633,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[76,114,16,115,78,131,83,25],"tags":[],"class_list":["post-64627","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-glm","category-goes-18","category-heavy-rain-flooding","category-lightningcast","category-noaa-20","category-noaa-21","category-nucaps","category-satellite-winds"],"acf":[],"_links":{"self":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/64627","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=64627"}],"version-history":[{"count":8,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/64627\/revisions"}],"predecessor-version":[{"id":64674,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/posts\/64627\/revisions\/64674"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/media\/64633"}],"wp:attachment":[{"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/media?parent=64627"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/categories?post=64627"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-json\/wp\/v2\/tags?post=64627"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}