The weather pattern during this USDM week (8/7/19-8/13/19) began with Tropical Storm Krosa bringing rain to the Marianas. The tropical storm strengthened to Typhoon Krosa but moved little in the following days; Krosa had moved out of the area by the end of the week. A monsoon trough extended through Krosa, across the Marianas, and into the central Federated States of Micronesia (FSM) for much of the week. A high pressure ridge to the south of Krosa dominated the weather all week over far western Micronesia (Palau and western Yap State). The Marshall Islands (RMI) and the eastern to central FSM were influenced, at various times, by surface troughs, trade-wind disturbances, trade-wind convergence, weak circulations, and upper-level divergence. The weather over American Samoa was dominated by a strong mid-level ridge.
Satellite-based estimates of 7-day precipitation (QPE) showed 4-10 inches of rain, and more, northwest of the Marianas associated with Krosa. Parts of central and especially northern Marianas were covered by the edge of this region, with 2-6 inches of rain indicated. Areas of 2-4 inches of rain extended in a band from the Marianas southeastward to the eastern FSM and parts of the RMI. Areas of 1-2 inches of rain extended east of this band over the rest of the RMI and to the west into Yap State. Little to no rain was indicated on the QPE over western Yap State to Palau. South of the equator, areas of 1+ inches of rain were indicated northwest of the Samoan Islands, but the QPE showed little to no rain over American Samoa.
Rainfall totals in the Marianas associated with Tropical Storm Krosa were highest on Saipan where 2.38 inches of rain was recorded this week. Rota saw 1.18 inches and Guam recorded 0.39 inch. Rainfall totals for the month of August are now over 11 inches for all three islands which is nearly three times the 4-inch monthly minimum needed to meet most water needs. Drought-free conditions remain on each island.
The Palau International Airport recorded only 0.25 inch of rain this week. However, this is the first dry week in a month and June (16.30 inches) and July (15.04 inches) were wet with rainfall each month nearly double the 8-inch monthly minimum needed to meet most water needs. Palau remains drought-free.
Despite it being a dry week for the western and central parts of the Federated States of Micronesia, the entire nation remained free of drought since July precipitation totals across the area were all above the 8-inch minimum, ranging from 10 to 19 inches. Yap (no rain), Woleai (0.57 inch), Chuuk Lagoon (0.56 inch; one day missing), and Lukunor (0.31 inch; one day missing) saw less than half the 2-inch weekly minimum needed to meet most water needs, while Kapingamarangi (1.16 inches) and Nukuoro (1.70 inches) were just below the 2-inch weekly threshold. Fananu (2.47 inches; two days missing), Pohnpei (2.98 inches; one day missing), Pingelap (7.88 inches; one day missing), and Kosrae (2.39 inches; one day missing) saw ample rainfall.
Jaluit was the driest of the Marshall Islands this week. Only 0.40 inch of rain was recorded this week which follows the driest July and June-July on record, and brings the August precipitation total to only 1.77 inches. Severe drought (D2-SL) remains for the island. Kwajalein saw rain every day this week which summed to 4.16 inches. Since this follows the 2.34 inches of rain last week, Kwajalein improved one category to moderate drought (D1-L). Ailinglapalap recorded 4.39 inches of rain this week which brings the rainfall total for the last three weeks to 10.44 inches. Abnormal dryness was removed from Ailinglapalap leaving D-nothing. Despite seeing a wet week, Majuro (3.99 inches) remains abnormally dry (D0-S) due to previously dry conditions and reservoir levels sitting around 28 million gallons, which is just below the critical 80% of capacity level. Wotje also met the 2-inch weekly threshold with 2.41 inches but remains in moderate drought (D1-SL) this week since it was improved one category last week. Utirik (2.43 inches) remains in severe drought (D2-SL). Mili saw 3.73 inches of rain this week and remains free of drought.
Dry conditions were found in American Samoa this week with Pago Pago reporting only 0.18 inch of rain. Other stations on the island reported closer to 0.40 inch. July, however, was wet with 17.54 inches of rain at Pago Pago, 11.70 inches for Siufaga Ridge, and 8.82 inches for Toa Ridge, so there are no concerns of dryness or drought at this time.