Trade wind convergence generated showers across the southern portions of Micronesia during this USDM week (4/10/19-4/16/19), while dry trades blowing out of the North Pacific subtropical ridge (North Pacific High) kept the weather dry across northern and western portions of Micronesia. A near-equatorial trough developed across southern portions of Palau and Yap State near the end of the week, along with a weak circulation in southeastern Yap State. The near-equatorial trough, weak circulation, and trade wind convergence comprised the Inter-Tropical Convergence Zone (ITCZ). Upper-level divergence enhanced the ITCZ convection near the end of the week. A weak cold front/shear line crossed the Marianas, but little rainfall resulted due to the very dry air. American Samoa was caught between a ridge to the north and surface trough to the south. The surface trough was part of the South Pacific Convergence Zone (SPCZ).
The ITCZ and SPCZ activity was reflected on satellite-based estimates of 7-day precipitation (QPE) as a broken band of 2-plus inches of precipitation across the southern portions of Micronesia. This band crossed the equator and turned southeast toward, then south of, the Samoan Islands. There were areas of 4-plus inches of rain within the ITCZ and SPCZ bands, mostly away from the primary USAPI weather stations. Little to no rainfall was indicated on the QPE across northern Micronesia, with less than an inch shown over American Samoa. (Summary by Richard Heim)
Dry conditions were found again this week in the Mariana Islands. Saipan received 0.27 inch rainfall while Rota and Guam saw 0.23 inch and 0.06 inch, respectively. These totals are all less than 30 percent of the 1-inch weekly minimum needed to meet most water needs. Drought impacts have also been significant. Guam has seen low stream flows, large brush fires, low surface soil moisture, brown grass, and trees dying. Meanwhile, impacts on Saipan include numerous fires, water salinity issues, cracks in soil, and tree crops suffering. With the recent low rainfall totals and observed impacts, Saipan was downgraded to exceptional drought (D4-S), Rota to severe drought (D2-S), and Guam to extreme drought (D3-S).
Palau saw 0.54 inch of precipitation this week. Rainfall totals have been below the 2-inch weekly minimum for all but two weeks since the beginning of February. February was well below the 8-inch monthly minimum (3.45 inches) and March was slightly less than 2 inches below the monthly minimum (6.24 inches). Precipitation was abundant last week (3.01 inches) and the week of March 13 (4.33 inches) but most other weeks has been less than an inch. Moderate drought (D1-S) remains.
The southern and eastern islands within the Federated States of Micronesia remain drought-free again this week. This week, Chuuk Lagoon (2.70 inches; one day missing), Nukuoro (3.94 inches; one day missing), and Kapingamarangi (2.18 inches; one day missing) exceeded the 2-inch weekly minimums needed to meet water needs. Lukunor (0.85 inch; two days missing), Pohnpei (0.54 inch), Pingelap (0.50 inch; one day missing), and Kosrae (1.30 inches; one day missing) saw somewhat dry conditions this week, but have had adequate precipitation in recent weeks and months leaving no concerns of dryness at this time. In contrast, Yap was downgraded to severe drought (D2-S) since no precipitation fell this week (two days missing), the 2-inch weekly minimum hasn’t been met for nearly three months, and February (1.57 inches) and March (4.88) were well below the 8-inch monthly minimum. Woleai received only 0.11 inch of rain this week (one day missing), but wetter conditions the last two weeks (4.55 inches and 1.73 inches) kept the island only abnormally dry (D0-S). Precipitation was just below the 2-inch weekly minimum this week on Fananu (1.87 inches; two days missing), so moderate drought (D1-S) remains.
Drought in the northern and central Marshall Islands remained and in some cases worsened this week. Wotje has now experienced its fourth consecutive week without precipitation and Utirik has seen its 12th consecutive week with less than 0.10 inch of rain (0.04 inch). Exceptional drought (D4-S) remains on the two atolls. Kwajalein was downgraded to extreme drought (D3-S) after the nearly complete absence of precipitation this week (0.09 inch) and reports of reverse osmosis units being distributed to some areas. Majuro saw more precipitation this week (0.84 inch) compared to last (0.15 inch) but still did not meet the 2-inch weekly minimum. Additionally, the Majuro reservoir remains below the critical 80% capacity level; people are foraging for water, and most home water catchments are depleted. Because water needs are not being met and impacts are becoming significant, Majuro was downgraded to extreme drought (D3-S). Ailinglapalap saw its third week in a row with less than 0.10 inch precipitation (0.09 inch), but remains abnormally dry (D0-S) due to abundant precipitation during a few weeks in March and February. Jaluit received only 1.01 inches of precipitation this week, but remains free of dryness and drought since last week was wet (3.74 inches) and minimum water requirements were met in March (8.73 inches). Mili saw only 1.10 inches of rain this week but remains drought-free thanks to wet conditions the last eight months.
Pago Pago went a third consecutive week with precipitation below the 2-inch weekly minimum (0.85 inch). However, the majority of the last nine months have seen wetter than normal conditions, leaving the area free of dryness.