Parts of interior Alaska received substantial rain, while showers mostly bypassed some locations. As a result, moderate drought (D1) was expanded slightly westward into central Alaska, but some dryness (D0) was eradicated in the east-central portion of the state. Interior Alaska’s largest active wildfire, the Munson Creek Fire, has burned more than 54,000 acres of vegetation.
In Hawaii, there were no changes to the drought depiction, despite an increase in the intensity of showers across windward locations, in part due to moisture associated with the remnants of eastern Pacific Tropical Storm Guillermo. In Hawaiian areas where rainfall has increased, low streamflow values were being monitored to gauge the impact of the shower activity.
The weather features across the U.S.-Affiliated Pacific Islands (USAPI) during this USDM week (07/21/21-07/27/21) included an expansive monsoon flow across western Micronesia. Tropical Storm Nepartak (11W) formed north of the Marianas at mid-week and helped intensify a monsoon trough west and north of the Marianas. The convergent monsoon flow drenched the Marianas with several inches of rain. Weekly totals ranged from 2.50 inches in the south at Guam to over 5 inches at Rota (5.77 inches) and the Saipan IAP (6.12), with over 8 inches estimated from satellite over the far northern Marianas. Over eastern Micronesia, the trade-wind pattern fell apart, with only weak circulations, disturbances, and surface troughs bringing areas of rain. South of the equator, easterly winds brought a few showers to American Samoa, but the weather for the week was mostly dominated by dry high pressure.
Satellite-based estimates of 7-day precipitation (QPE) are available from two products: one using mainly infrared (IR) sensors (NESDIS GOES-R AHI) and the other incorporating microwave sensors (GPM IMERG). These QPE products showed a huge arch of 4+ inches of rain that stretched in the shape of a U from the northern Chinese coast, to the Marianas, then northeastward, associated with the monsoon trough and TS Nepartak. A patchy band of 1+ inches stretched eastward across Palau, the Federated States of Micronesia (FSM), and the southern Marshall Islands (RMI). The satellite QPE detected only a few tenths of an inch of rain over American Samoa.
As noted earlier, it was a wet week in the Marianas, with rainfall totals consistently over 2 inches (one inch is the weekly minimum needed to meet most water needs in the Marianas), so D-Nothing continued. Further south, the monsoon rains delivered weekly precipitation totals (based on rain gauge amounts received for the week) over 2 inches to Woleai (3.41 inches) and Yap (2.56), but under 2 inches to Ulithi (1.20 inches with 3 days missing). In Palau, Airai recorded 1.71 inches and the Koror COOP station 0.94 inch. Rain earlier in the month resulted in July month-to-date totals at these stations that were above the monthly minimum needed to meet most water needs. Kosrae (3.28 inches) and Nukuoro (3.94 inches) were wet (above the weekly minimum) while the rest of the FSM stations were dry, with values ranging from 0.23 inch at Lukunor to 1.83 inches at Kapingamarangi. Except for Lukunor, the month-to-date totals were above the monthly minimum at the FSM stations. D-Nothing continued at Palau and the FSM stations except for Fananu, which was not analyzed due to no data.
It was a dry week in American Samoa, with Pago Pago recording 0.37 inch and the automated stations at Siufaga Ridge (0.73 inch) and Toa Ridge (0.28 inch) below an inch (the automated stations had one day missing). But month-to-date totals were wet, so D-Nothing continued at Tutuila.
In the RMI, Kwajalein was wet (above the 2-inch weekly minimum) with 2.31 inches of rain for the week. But the rest of the stations were dry, with weekly rainfall totals ranging from 0.40 inch at Jaluit to 1.50 inches at Majuro. Ailinglaplap recorded 0.55 inch for the week and 2.43 inches so far this month. This week marked the fourth consecutive dry week, and July 2021 (based on data received so far in the month) marked the third consecutive dry month. Compared to historical full Julys, July 2021 was the driest July in the 37-year record, June-July 2021 was the driest such 2-month period, and May-July 2021 was the driest May-July. Jaluit reported 0.40 inch of rain for the week and 3.22 inches so far this month. This week marked the seventh consecutive dry week. Compared to historical full Julys, July 2021 ranked as the second driest July in 38 years of data, June-July 2021 was the fourth driest June-July, and May-July 2021 was the ninth driest such 3-month period. D0-S continued at Ailinglaplap and Jaluit. At the other RMI stations, either July-to-date has been wet (Kwajalein and Mili), or previous weeks have been wet, so D-Nothing continued. Of concern is the declining reservoir level at Majuro; as of July 26, about 27 million gallons were in the reservoir, which is below the threshold for concern of 28.8 million gallons. The drought status at Utirik could not be analyzed due to lack of data.
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