A dry trade-wind regime dominated the weather pattern during this USDM week (7/03/19-7/09/19) across northern portions of Micronesia while areas of convection associated with various features of the Inter-Tropical Convergence Zone (ITCZ) brought rain to southern parts. The ITCZ features included surface troughs, weak circulations, and converging winds. Upper-level troughs and lows were also present, with TUTT (Tropical Upper-Tropospheric Trough) cells in the north, and their associated upper-level divergence enhanced showers in some areas. Precipitation from the TUTTs in the north, especially over the Marianas, was limited due to the lack of deep layer moisture. South of the equator, a high pressure ridge generated strong trade winds across American Samoa and kept a surface trough, with its heavier convection, to the north and west of the islands during most of the week.
Satellite-based estimates of 7-day precipitation (QPE) showed a large area of 2+ inches of rain across southeastern portions of the Federated States of Micronesia (FSM), and some 2+ inch areas just west of Palau and Yap State, just east of the Republic of the Marshall Islands (RMI), and north of 10 degrees North latitude, with less than an inch of precipitation indicated between these areas. The northern rain areas were associated with upper-level troughs and lows, while the southern areas were caused by ITCZ convection. The southeastern FSM rain area extended south of the equator, southeastward toward the Samoan Islands. The QPE maps showed a sharp gradient of precipitation in the Samoan area, with 4+ inches over the western Samoan Islands to less than half an inch east and south of American Samoa.
After a wet week, dry conditions returned to Palau, receiving only 0.97 inch of rain this week. Since this is less than the weekly minimum of 2 inches, abnormally dry (D0-S) conditions continued to affect Palau this week.
Dry conditions were present this week in the Marianas, with two of the three stations analyzed receiving less than half their weekly minimum of 1 inch. The station with the least rain was Saipan, receiving only 0.23 inch of rain. Guam followed with a rainfall total of 0.28 inch. Rota had the most rainfall at 0.95 inch of rain for the week. All three stations continued to be in extreme drought (D3-S).
Six (Chuuk, Pohnpei, Kosrae, Nukuoro, Lukunoch, and Pingelap) of 11 stations analyzed had precipitation totals that equaled or surpassed the 2 inch minimum threshold to meet most water needs. The station with the most precipitation was Nukuoro at 4.46 inches of rain for the week. Chuuk, Pohnpei, Kosrae, Nukuoro, Lukunoch, and Pingelap continued to be drought free (D-Nothing) this week.
However, Yap, Fananu, Kapingamarangi, and Woleai had a dry week. The station with the least precipitation was Fananu (0.15 inch; with 1 day of missing data). Although Fananu had 8 inches of rain for the month of June, the last two weeks have been extremely dry, with less than half of an inch of rain for the two weeks combined. For this reason moderate drought (D1-S) persists once again this week. This week Yap’s precipitation total of 1.88 inches was only 0.12 inch shy of reaching its 2 inches weekly minimum, helping maintain its drought classification of abnormally dry (D0-S). Kapingamarangi and Woleai remained drought free (D-Nothing) since this week marks the first or second consecutive week of dry conditions for these locations.
No data was available for Ulithi and thus was set to missing.
All of the stations analyzed in the Marshall Islands had little rain during the week, with Wotje reporting no rain. Jaluit and Ailinglapalap were the other two stations with the least precipitation totals at 0.20 inch and 0.30 inch, respectively. Jaluit’s drought classification of moderate drought (D1-S) continued this week as dry conditions affected the area since April 2019. Since this was Ailinglapalap and Mili’s first or second consecutive dry week and the month of June surpassed the 8-inches threshold to meet most water needs, drought free (D-Nothing) conditions persisted for both locations.
Kwajalein had a total of 0.85 inch of rain for the week, which is 1.15 inches of rain less than the weekly minimum of 2 inches. As dry conditions continued, Kwajalein remained in moderate drought (D1-S). The last two weeks have been very dry in Majuro, with precipitation totals less than 1 inch of rain and reservoir levels dropping. As of July 3, reservoir levels were at 77% of the maximum capacity of 36 million gallons and below the critical 80% threshold. Abnormally dry (D0-S) drought classification was unchanged this week.
Exceptional drought (D4-SL) continued to affect Wotje and Utirik since dry conditions have persisted since the end of 2018.
Pago Pago had its third consecutive dry week, with precipitation totals less than 1 inch and the month of June had less than 8 inches required to meet most water needs. For this reason, abnormal dryness (D0-S) was introduced to Pago Pago.