The weather across the U.S.-Affiliated Pacific Islands (USAPI) during this USDM week (01/13/20-01/19/21) was dominated by a persistent surface trough across western Micronesia and a pronounced Inter-Tropical Convergence Zone (ITCZ) across eastern Micronesia which at times extended into western Micronesia. Other smaller surface troughs or trade-wind disturbances made appearances in the region, a weak circulation developed near Palau and western Yap State, and a trade-wind disturbance crossed the northern RMI. A couple weak disturbances crossed the Marianas, but the weather there was mostly dominated by a dry trade-wind air mass. South of the equator, a weak trough moved across the Samoan Islands early in the week, but otherwise a high pressure ridge dominated the weather.
Satellite-based estimates of 7-day precipitation (QPE) showed a band of 2+ inches of rain across Palau and Yap State extending from about 2 degrees North latitude to 10 N in places. The band stretched eastward along the ITCZ across the rest of the Federated States of Micronesia (FSM) and Marshall Islands (RMI) but narrowed, reaching from roughly 5 N to 8 N over the RMI. Within the band, a large area of 4+ inches of rain stretched the length of the region, with lesser amounts (0.5 to 2.0 inches) extending to the equator in places across western and central FSM. Little to no precipitation was analyzed in the QPE across the Marianas and Samoan Islands.
Conditions have been relatively dry in the short term in American Samoa, though not at the level of abnormal dryness. Suifaga Ridge received 1.12 inches of rain this week, Toa Ridge reported 0.75 inches, and 0.67 inches fell at Pago Pago.
At Palau, 2.39 inches of rain fell this week, and 1.97 inches fell at Koror, so drought-free conditions continued there.
The Federated States of Micronesia remained mostly free of drought or dryness this week, with the significant exception of Kapingamarangi. At least 2.04 inches of rain fell this week on Yap after 4.08 inches there last week. Ulithi received 4.09 inches of rain this week. Woleai received only 0.36 inches this week, marking their third consecutive week below their weekly minimum, though conditions have not quite degraded to abnormal dryness. Fananu only received 0.26 inches of rain this week, but conditions here haven't degraded to abnormal dryness, as 4.88 inches fell last week and 10.17 inches fell three weeks ago. Chuuk had 3.89 inches of rain this week, so normal conditions continued there. Normal conditions also continued on Lukunoch, where 3.20 inches fell. Nukuoro had 3.59 inches of rain this week, following 8.51 inches last week, so wet conditions persisted. Exceptional short- and long-term drought continued on Kapingamarangi despite 2.30 inches of rain this week. This marked the first week since the beginning of December where their weekly minimum was reached, and no monthly minimum rainfall has been reached there since April 2020. Pohnpei's wet conditions continued this week with 3.81 inches of rain. On Pingelap, 0.83 inches of rain made for a drier week, but the January minimum rainfall has already been met, and December 2020 rainfall was at the 97th percentile, so conditions here remained wet. Another rainy week took place on Kosrae, as last week's 12.40 inches of rain were followed up by another 6.53 inches.
Short-term abnormal dryness developed on Saipan, where rainfall amounted to 0.48, 0.33, and 0.07 inches at three different measuring sites this week. This was the sixth consecutive week when precipitation fell below their weekly minimum. Rota only received 0.21 inches of rain this week, thus falling below their weekly minimum for the fifth time in the last six weeks. However, the last week of December saw 4.04 inches of rain, so conditions have not yet degraded to short-term abnormal dryness at Rota. Only 0.48 inches of rain accumulated on Guam this week, the fifth consecutive week below their weekly minimum, though conditions have not quite degraded to abnormal dryness.
The Marshall Islands remained free of drought this week, though short-term abnormal dryness was taking place on Kwajalein and Wotje. On Kwajalein, 1.48 inches of rain fell this week, marking the 7th consecutive week below weekly minimum rainfall there. With 4.02 inches, December also missed its monthly minimum, so short-term abnormal dryness continued. On Wotje, short-term abnormal dryness has continued to take hold, as the 0.95 inches of rain this week was the first measurable rainfall of 2021. Data are missing this week from Utirik, so no drought depiction is being made there. On Jaluit, 0.67 inches of rain this week followed 3.23 inches last week, so normal conditions continued there. Majuro received 3.15 inches of rain for the second consecutive week and remained free of drought this week. Mili remained free of drought as 4.27 inches of rain fell this week.