{"id":51529,"date":"2023-04-06T14:15:00","date_gmt":"2023-04-06T14:15:00","guid":{"rendered":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/?p=51529"},"modified":"2023-04-06T20:11:08","modified_gmt":"2023-04-06T20:11:08","slug":"an-airmass-change-at-guam","status":"publish","type":"post","link":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/archives\/51529","title":{"rendered":"An airmass change at Guam"},"content":{"rendered":"\n
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Himawari-9 Airmass RGB imagery, 0000 UTC on 4 April to 1200 UTC on 6 April 2023 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

Himawari-9 Airmass RGB imagery<\/a>, below, from 0000 on 4 April through 1200 UTC on 6 April 2023 (created using geo2grid<\/a>) show a transition from a deep tropical airmass (deep green in the RGB with embedded clouds that are white) over the southern Marianas islands to one that is a bit dryer (more orange in the RGB). A meteorogram for the A. B. Won Pat International Airport on Guam, below, shows the transition that started around 1800 UTC on 4 April. In particular, the pressure increased from 1008 mb to around 1010 mb; winds shifted to northeast and then east (and strengthened); dewpoint temperatures dropped a couple degrees (o<\/sup>F). Guam is at 13.4\u00b0 N; this airmass penetrated very deep into the tropics.<\/p>\n\n\n\n

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Meteorogram for PGUM, ca. 0000 UTC on 3 April 2023 through 1800 UTC on 6 April 2023 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

What other satellite products showed this change? The Night Microphysics RGB<\/a>, below, also shows a boundary moving south over the southern Marianas islands. As with the airmass RGB above, the boundary does not appear to move very far south of Guam.<\/p>\n\n\n\n

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Nighttime Microphysics RGB, 0000 UTC 4 April to 1200 UTC 6 April 2023 at 12-hour intervals (click to enlarge)<\/figcaption><\/figure>\n\n\n\n

Advanced Scatterometer (ASCAT) imagery from MetopB and MetopC (originally from this website<\/a>, and combined into one image at this website<\/a> that shows the most recent 1-week animation) also shows the expansion southward of strong northeasterly winds. On 3 April 2023<\/a>, winds around Guam are light from the east or southeast. By 5 April 2023<\/a>, strong northeasterly winds have expanded southward over the Marianas Islands.<\/p>\n\n\n\n

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ASCAT winds from MetopB and MetopC, 3 – 5 April 2023 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

ASCAT winds ca. 1200 UTC on 6 April 2023, shown below, indicate strong convergence over Guam.<\/p>\n\n\n\n

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ASCAT winds from MetopC (left, 1117 UTC) and MetopB (right, 1204 UTC) on 6 April 2023 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

Gridded NUCAPS fields (available at this site<\/a>) also show the stark differences across the Marianas Islands from north to south. The animation below shows 850-700 mb lapse rates (more stable over the northern Marianas), 400-200 mb lapse rates (more stable over the northern Marianas), Total Precipitable water (dryer over the northern Marianas) and 850-mb Temperatures (cooler over the northern Marianas). NUCAPS data can give very useful information within data voids (like the Western Pacific Ocean!)<\/p>\n\n\n\n

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Gridded NOAA-20 NUCAPS data estimates of 850-700 mb Lapse Rates, 400-200 mb Lapse Rates, Total Precipitable Water, 850-mb Temperatures, s<\/figcaption><\/figure>\n\n\n\n

MIMIC Total Precipitable Water fields over the western Pacific Ocean (from this site<\/a> and archived here<\/a>), below, from 0000 UTC on 1 April through 1200 UTC 6 April, show the dramatic southward motion of dry air over the northern Marianas that extend northeastward from Guam (at 13.4\u00b0 N, 144.8\u00b0 E).<\/p>\n\n\n\n

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MIMIC TPW, 0000 UTC on 1 April to 1200 UTC on 6 April 2023 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n
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Sandwich product imagery from this JMA website<\/a> (scraped daily), below, shows parts of the western Pacific from 0000 UTC on 1 April through 5 April 2023. The storm responsible for dragging a front across the Marianas is apparent in the imagery starting around 3 April.<\/p>\n\n\n\n