{"id":56651,"date":"2024-01-23T06:54:00","date_gmt":"2024-01-23T06:54:00","guid":{"rendered":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/?p=56651"},"modified":"2024-01-26T17:51:39","modified_gmt":"2024-01-26T17:51:39","slug":"large-waves-over-the-central-and-south-pacific-ocean","status":"publish","type":"post","link":"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/archives\/56651","title":{"rendered":"Large waves over the Central and South Pacific Ocean"},"content":{"rendered":"\n

Damaging waves hit the Marshall Islands on 19 January 2024<\/a>, causing considerable damage, and the northern shores of American Samoa on 22 January 2024, leaving behind considerable debris, as shown below (photos courtesy NWS Pago Pago).<\/p>\n\n\n\n

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Debris deposited by large waves in Fale?sao, Manu\u2019a, American Samoa, 22 January 2024 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n
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Debris deposited by large waves in Maloata, Tutuila, American Samoa, 22 January 2024 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

The waves could be tracked using Altimetric data as viewed at this NOAA\/NESDIS website<\/a>; data for the globe and also data around the Marshall Islands were saved from that website and shown below. A second website (that contains data over South Pacific around Samoa<\/a>, which data are routinely taken from the NOAA\/NESDIS website and stitched into a larger field) was used to save imagery around American Samoa as shown below. Plots at these websites show Significant Wave Height, that is, the mean of the highest 1\/3rd of the waves. The global animation, below, centered on the Pacific, shows a region of higher waves moving southward through the western Pacific; stars show the location of the Marshall Islands (20 January) and American Samoa (22 January), at the approximate time of the waves’ arrival at those locations.<\/p>\n\n\n\n

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Altimetric observations of Significant Wave Heights, 0000-1200 UTC observations, 15-23 January 2024 (Click to enlarge). The orange line shows the boundary between <12 and >12 foot waves; Stars show the Marshall Islands (20 January) and American Samoa (22 January), the approximate times of the large waves.<\/figcaption><\/figure>\n\n\n\n

The animation below is zoomed in over the Marshall Islands, and covers 0o<\/sup> to 20o<\/sup>N Latitude, 180-150o<\/sup>E Longitude. Note the southward progression of progressively larger waves through the animation. The purple box is the approximate location of Roi-Namur, the island where the damage discussed in the Army Times article above occurred.<\/p>\n\n\n\n

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Altimetric Observations of Significant Wave Height over the central Pacific, 17-20 January 2024, times as indicated. The location of Roi-Namur in the Marshall Islands is indicated by the purple box. A Green Arrow shows a boundary between waves <12 Feet and >12 Feet; note its southward progression during this time (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

The animation below shows American Samoa (highlighted in the Green Box). Wave heights increase from around 7 to 11 feet in advance of the large waves’ arrival on Tutuila and Manu’a. A High Surf warning<\/a> was issued by the forecast office in Pago Pago.<\/p>\n\n\n\n

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Altimetric observations of Significant Wave Height, 21-22 January 2024, times as indicated. (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n
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What caused these waves? Forecast model output (courtesy Eric Lau, NWS PRH), below, shows hurricane-force winds (in yellow, between 160o<\/sup> and 170o<\/sup>E longitude) generated by a potent extratropical cyclone to the east of Japan. The strong winds are present for about 24 hours, and the region of strongest winds translates with the predicted wind direction. The similarities between the wind direction and the motion of the speed maximum suggest that dynamic fetch<\/a> may have been responsible for the extraordinary waves.<\/p>\n\n\n\n

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GFS Forecast Surface Winds, 1200 UTC 17 January 2024 – 1200 22 UTC January 2024 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

WPC<\/s> OPC analyses<\/a>, below, (also from Eric Lau) show the rapid development of the storm from 1003 mb on 1200 UTC.16 January 2024 to 964 mb on 1200 UTC\/17 January 2024. The storm started to weaken starting at 1200 UTC\/18 January 2024.<\/p>\n\n\n\n

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WPC Surface Analyses every 6 hours from 0000 UTC 16 January 2024 to 0000 UTC 19 January 2024 (Click to enlarge)<\/figcaption><\/figure>\n\n\n\n

What did the satellite data look like during this time period? The airmass RGB animation, below, (created from geo2grid<\/a> using Himawari-9 data supplied by JMA<\/a>), shows the development of a strong, but not necessarily unusually strong, storm. Recall that the strongest winds were predicted to be between 160 and 170o<\/sup>E, from 1200 UTC on the 17th to 1800 UTC on the 18th.<\/p>\n\n\n\n