During the Northern Hemisphere winter months, dry northeast trade winds emanating from the North Pacific High shift southward, and the Inter-Tropical Convergence mechanisms also shift southward and are not as active as in the summer months. This pattern brought dry weather to northern portions of Micronesia during this USDM week (02/10/21-02/16/21), notably the Marianas and northern Marshall Islands (RMI). Further south in these U.S.-Affiliated Pacific Islands (USAPI), a near-equatorial trough with a weak circulation dominated the weather over Palau and much of Yap State, while trade-wind convergence and embedded surface troughs brought rain to central and eastern parts of the Federated States of Micronesia (FSM) and southern parts of the RMI. Cold front/shear line fragments teased the Marianas but brought little rain. South of the equator, a normally active South Pacific Convergence Zone (SPCZ) makes this time of year (summer in the Southern Hemisphere) the wettest season for the Samoan Islands. But this week the SPCZ was shifted to the west with a ridge of high pressure dominating the weather over American Samoa.
Satellite-based estimates of 7-day precipitation (QPE) showed a large band of 2+ inches of rain stretching across Palau and much of the FSM, with embedded areas of 4+ inches. A band of 2+ inches of precipitation was evident over southern parts of the RMI. These reflected the broad circulation and trough in the west and the narrower region of trade-wind convergence in the east. Little to no rainfall was indicated on the QPE north of these bands, where drier trade winds dominated, or across southern parts of Chuuk and Pohnpei States. The QPE revealed areas of 1+ inches of rain west and northeast of the Samoan Islands, with streaks of half an inch or more across American Samoa between these areas.
The Republic of Palau remained free of dryness. Palau IAP received more than 2 inches, while Koror COOP reported 5.24 inches.
The Mariana Islands remained dry with Rota and Saipan experiencing continued abnormal dryness, while abnormal dryness was introduced this week for Guam. Precipitation for Guam was only 0.02 inches, although one inch of rain weekly is needed to meet minimum water needs. Grass was beginning to turn brown and become crunchy on Guam. Rota reported 0.12 inches for the week. Rainfall at Saipan IAP was 0.36 inches, at Saipan ASOS was 0.59 inches, and at Saipan NPS was 0.18 inches.
The Federal States of Micronesia were mostly wet for the week with a couple of drier locations. Fananu remained abnormally dry, reporting 0.74 inches. All other FSM locations, apart from Kapingamarangi, received from 2 to nearly 10 inches. Kapingamarangi remained at D3 after receiving 0.87 inches for the fourth week of less than an inch of rain. Conditions were dire for Kapingamarangi and a state of emergency was declared by the state. Well water has been unsafe to drink since possibly September or October. Some springs were dry, and streams have been low for roughly three weeks. Residents were able to fill all of their reserve water catchment tanks at the end of January, but the large community concrete water tank remained low. At present, personal private tanks were around one-fourth of capacity and the community concrete tank was just below half. IOM and the Micronesia Conservation Trust both sent eight 1,600 gallon water tanks on the last trip to Kapingamarangi. Pohnpei State will be transporting food to Kapingamarangi in coming days as all crops were in in very bad shape, especially taro and breadfruit.
Conditions continued to be mixed for the Marshall Islands with some locations abnormally dry or in drought. Kwajalein and Wotje remained at D2 as Kwajalein received 1.17 inches, while Wotje reported no rain for the past week. Jaluit continued to be abnormally dry, reporting 0.85 inches. Ailinglaplap, Mili and Majuro received 1.99 inches to nearly four inches. The Majuro reservoirs held 27.357 million gallons on Feb. 15 after benefiting from recent rain and hold 36 million gallons at capacity.
American Samoa remained free of drought. Pago Pago received 0.86 inches, Siufaga Ridge reported 2.25 inches, and Toa Ridge received 1.38 inches.