The weather pattern during this USDM week (9/4/19-9/10/19) consisted of a continued monsoon trough from the Marianas, northern Palau, and northwest Yap State, southeastward across the Federated States of Micronesia (FSM) to the southern Marshall Islands (RMI). Weak circulations embedded within the monsoon trough slowly migrated westward during the week. Upper-level troughs to the north of the USAPI created a divergent flow aloft that extended over parts of Micronesia, especially in the west, which combined with the monsoonal convergence at the surface to enhance showers and thunderstorms. South of the equator, a surface convergence zone (trough/stationary front) oscillated across the Samoan Island region, competing with stable and more drier air extending into the region from the south and east.
Satellite-based estimates of 7-day precipitation (QPE) showed a mostly continuous band of precipitation extending from the East China Sea and Philippine Sea southeastward across Micronesia into the Southern Hemisphere. Over Micronesia, precipitation amounts in this band were estimated at 2 to 4 inches, with locally up to 10 inches or more, and the rain delineated the monsoon trough. Rainfall amounts tapered off to an inch or less across southwestern Micronesia and over extreme northeastern FSM. South of the equator, the rain band comprised a patchy South Pacific Convergence Zone extending across the Samoan region which was characterized by areas of 2 to 4 inches of rain next to pockets of less than an inch.
The Republic of Palau continued to experience showery weather, with a month-to-date total of 5.81 inches of rain reported at the international airport through the afternoon of September 10. As a result, D-nothing continued.
A showery pattern also persisted in the Mariana Islands, with all major observation sites receiving at least 3 inches of rain during the monitoring period. A D-nothing designation continued throughout the Marianas. Through September 10, month-to-date rainfall totaled 4.37 inches (126 percent of normal) at Saipan/Isley.
In the Federated States of Micronesia, most islands remained wet enough to retain a D-nothing designation. Weekly totals ranged from 6 to 10 inches in several locations, including Fananu, Kosrae, Pohnpei, and Chuuk Lagoon, with nearly all other islands receiving the 2-inch weekly minimum value. One exception was Pingelap, where D0-S was retained due to a weekly sum of 1.30 inches (with 2 days of data missing). Elsewhere, no data was reported from Ulithi and thus no analysis was made.
In the Republic of the Marshall Islands, variable rainfall was generally light or moderately heavy, with most observation sites receiving 1 to 3 inches during the drought-monitoring period. Jaluit remained at D2-SL after receiving 1.11 inches during the week. Meanwhile, short-term dryness was replaced by D-nothing at Kwajalein and Ailinglapalap, courtesy of weekly totals that reached 3.11 and 2.73 inches, respectively. Utirik also received appreciable rain, 3.20 inches, resulting in improvement from moderate drought to abnormal dryness (D1-L to D0-L). Rainfall was a bit lighter at Wotje, where 1.78 inches fell, leaving D1-SL intact. Mili and Majuro retained a D-nothing designation, although the latter location is teetering on the brink of short-term dryness. Majuro's weekly rainfall totaled 1.07 inches, following an August that featured more than 13 inches. Majuro's reservoir storage has been dropping in recent days, but stood at 28.838 million gallons (80.1 percent of capacity) on September 11.
In American Samoa, rainfall has been generally light since late August, and D0-S was introduced last week. During the drought-monitoring period, less than an inch of rain fell at two National Park Service observation sites. Rainfall was a little heavier at the Pago Pago Airport, with 1.32 inches reported for the week. Through September 10, the month-to-date rainfall at the airport totaled just 1.35 inches. As a result, D0-S was retained for American Samoa.