August 2, 2022 National Drought Summary

The discussion in the Looking Ahead section is simply a description of what the official national guidance from the National Weather Service (NWS) National Centers for Environmental Prediction is depicting for current areas of dryness and drought. The NWS forecast products utilizedinclude the HPC 5-day QPF and 5-day Mean Temperature progs, the 6-10 Day Outlooks of Temperature and Precipitation Probability, and the 8-14Day Outlooks of Temperature and Precipitation Probability, valid as of late Wednesday afternoon of the USDM release week. The NWS forecast webpage used for this section is: http://www.cpc.ncep.noaa.gov/products/forecasts/.

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Patches of moisture embedded in the trade wind flow, and a tropical wave, alternated with a dry air mass over the U.S. Virgin Islands (USVI) during this USDM week (July 27-August 2). A Saharan dust layer made its way into the region late in the week, limiting the potential for rainfall activity. The shower activity resulting from the tropical wave and trade wind flow produced the greatest rainfall amounts in the south (St. Croix) with lesser amounts in the north (St. John and St. Thomas). Satellite observations of vegetative health (VHI) showed some improvement in recent weeks on St. Croix, and groundwater levels on the island fluctuated up and down during the last couple weeks. The VHI showed significant to severe impacts to vegetation continuing on St. John and St. Thomas, and groundwater levels continued their steady decline since February on these islands. The groundwater levels were at or near record low levels, based on the 2016-2022 record, at the gauges on all 3 islands.

Weekly rainfall totals on St. Croix ranged from 0.28 inch to 1.72 inches, with reports of half an inch or more common. Rohlsen AP received 1.26 inches for the week and 4.15 inches for the month of July, which was 157% of normal. Previous months were dry, with March 1-August 1, 2022 ranking as the 4th driest such period in 63 years of data. The year-to-date precipitation total was 89% of normal. But with improving vegetation (VHI) and Standardized Precipitation Index (SPI) values, and the decline in groundwater levels temporarily stopped, the status on St. Croix was improved to D2-SL.

On St. Thomas, weekly rainfall totals ranged from 0.11 inch to 0.80 inch, with the King AP recording a mere 0.13 inch. The July 2022 total at King AP was 1.99 inches, which is 68% of normal, and the year-to-date total was only 77% of normal. Recent months were dry, with May 1-August 1, 2022 ranking 3rd driest for the period in 58 years of data, and April 1-August 1 ranking 4th driest. The groundwater level set a new record low value (in the 2016-2022 record) on July 31. SPI values held steady or got slightly worse, so D2-SL continued for St. Thomas.

St. John was dry this week, with rainfall totals ranging from 0.17 inch to 0.28 inch. Three (3.02) inches of rain fell at the weather station at Windswept Beach during July, but the year-to-date total was only 72% of the long-term average. The VHI showed severely dry vegetation that was not improving in recent weeks and the groundwater level at the USGS Susannaberg DPW 3 Well was at the lowest level since November 2016. SPI values mostly held steady or got slightly worse, so D3-SL continued for St. John.

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The Inter-Tropical Convergence Zone (ITCZ) and trade-wind troughs spread rain across the middle third of Micronesia during this USDM week (July 27-August 2). A tropical disturbance, trade-wind troughs, and a Tropical Upper-Tropospheric Trough (TUTT) alternated during the week to bring abundant rain to the Marianas and other portions of western Micronesia. High pressure and stable air dominated American Samoa for much of the week, but showers embedded in the easterly trade-wind flow were common at times.

Several inches of rain fell across the Marianas this week, with Guam reporting 4.25 inches, Rota 5.40 inches, and Saipan IAP 6.30 inches. In the Republic of Palau, over 6 inches was recorded at the Koror COOP station. Two inches or more of rain fell across a middle stretch of the Federated States of Micronesia (FSM) and the Marshall Islands, while southern portions had a dry (less than 2 inches) week. It was a dry week in American Samoa, where Pago Pago recorded only 0.65 inch and about an inch (0.98) fell at the automated stations at Siufaga Ridge and Toa Ridge. But the month of July was wet across most of the U.S.-Affiliated Pacific Islands, with most locations reporting more than the 4-inch or 8-inch monthly minimum needed to meet most water needs. Only Fananu reported less than the 8-inch minimum (4.46 inches was reported), and this may be due to some missing data. Other than Lukunor, Kapingamarangi, and Nukuoro, those stations that had less than the 1- or 2-inch weekly minimum this week were wet (above the weekly min) last week and previous weeks.

Lukunor and Nukuoro have been dry (less than the weekly min) for the last 2 weeks, but previous weeks were wet and the July totals were well above the monthly minimum, so D-Nothing (no drought or abnormal dryness) continued for these locations. D-Nothing continued for the rest of the analyzed locations except Utirik (which had no data and was plotted as missing) and Kapingamarangi.

Fananu reported 4.93 inches of rain in the last two weeks but only 4.46 inches for the month of July (which is below the 8-inch monthly minimum needed to meet most water needs). With 2.20 inches of that 4.93 inches falling on August 1-2, Fananu was analyzed as D-Nothing.

Kapingamarangi had 8.60 inches for July, which is above the 8-inch monthly minimum, but the last 2 weeks have been dry (below the 2-inch weekly minimum) (0.88 inch last week and 0.57 inch this week). July 2022 ranks as the 10th driest July in 33 years of data, but June-July ranks 4th driest; May-July, April-July, and March-July rank driest on record; and the rest of the time periods from February-July (last 6 months) to August-July (last 12 months) rank 2nd or 3rd driest. The July 22 Drought Information Statement from the National Weather Service noted impacts continuing: Public and private water tanks are not replenished but above 50%, and vegetation is still yellow. With the last 2 weeks dry, percentiles for all time scales from the last 2 to 6 months (S) and 7 to 12 months (L) dry, and impacts continuing, the status at Kapingamarangi was changed from D1-L to D1-SL.

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