Summary

August 8, 2019 - Heavy rain fell on large parts of Alaska this past week, bringing significant short-term relief, including an end to large fire development and expansion, at least for the time being. In contrast, dryness and drought expanded across broad sections of the contiguous 48 states, with relief restricted to parts of the Southeast. Most notably, hot and dry weather brought significant D0 expansion in the southern half of the Great Plains and across the Midwest and lower Ohio Valley. In the Northeast Climate Region, a few abnormally dry areas were introduced; this is only the fourth week since mid-January that dryness existed in any part of the Region. Meanwhile, heavy rain in eastern Puerto Rico improved conditions over eastern parts of the Commonwealth.

Northeast

A broken pattern of moderate to locally heavy rain (up to 3 inches) affected the region this week, primarily from southern New York through Pennsylvania and eastern West Virginia. Over the past month, rainfall totals were 2.0 to 3.5 inches below normal in a few scattered areas in western West Virginia, southwestern New England, upstate New York, and lower Maine, prompting D0 introduction in those areas. In southwestern New England, upstate New York, and part of southwestern West Virginia, totals are 2 to locally 6 inches below normal since early June.

Southeast

Precipitation varied markedly across the region, which is typical for summer. Generally, heavy rain fell around the periphery of the dry areas in Alabama, much of Georgia, and northern South Carolina, leading to some reduction in D0 to D2 coverage. D0 was removed entirely from southeasternmost Georgia and northeastern Florida. In contrast, areas that missed most of the rain experienced limited deterioration. Small-scale expansion of D0 and D1 was noted in south-central and eastern Georgia, and southern South Carolina. In most dry areas, the last 60 days brought 2 to locally over 6 fewer inches of rain than normal, and 50 to 75 percent of normal during the past month.

South

Another drier-than-normal week affected central and eastern sections of Texas and Oklahoma as well as the northern tier of Louisiana, where little or no rain was reported. Recent hot and dry weather there has spawned broad development of D0 and D1 conditions in the south-central Plains, with severe drought introduced in southwestern Oklahoma and adjacent Texas. Broad swaths of central and western Oklahoma, the Texas Panhandle, and southwestern Texas recorded only a few tenths of an inch of rain at best over the last 30 days, and about 25 to 60 percent of normal since early June.

Midwest

Generally 0.5 to 2.0 inches of rain fell last week on central and southern Wisconsin, but most of the region recorded only a few tenths of an inch, if any. The last 30 days brought only 10 to 50 percent of normal rainfall to most areas from central Iowa through east-central Illinois and part of western Indiana, with the largest deficits affecting a swath from east-central Iowa southeastward through central Illinois. Abnormal dryness was expanded extensively to cover this region, plus sections of southwestern Ohio, northeastern Kentucky, and southern Indiana, where rainfall has been slightly more generous. Since early June, 40 to 75 percent of normal rain has been recorded in central and eastern Iowa and adjacent Illinois. Farther north and west, patches of D0 persisted in and near the Upper Peninsula of Michigan, northeastern Minnesota, and southeastern Michigan. No drought exists in the region at this time, though aforementioned sections of Iowa and Illinois are approaching D1.

High Plains

It was a dry week in and near existing areas of dryness and drought. Broad expansion of abnormal dryness occurred across central and southern Kansas, where conditions have deteriorated quickly as in Oklahoma and Texas. Much of central and south-central Kansas received 0.5 inch or less of rainfall over the last 30 days. In the rest of the region, D0 and D1 conditions generally persisted, with very limited expansion brought into parts of northern North Dakota, east-central Nebraska, and southeastern Colorado.

West

Severe drought persisted in portions of northwestern Washington where only 40 to 75 percent of normal precipitation fell during the past six months. Light to locally moderate rain fell this week from central Arizona through central New Mexico, and across portions of southern and eastern Montana. Other areas recorded very little or none. Increasing moisture deficits induced moderate drought expansion into northwestern New Mexico while D0 expanded in southeastern Washington and across northern Montana. Conditions were unchanged in other areas. The past 60 days brought only 25 to 50 percent of normal rainfall to the new moderate drought area in northwestern New Mexico.

Alaska, Hawaii, and Puerto Rico

Heavy precipitation and cooler temperatures brought widespread improvement to central and northern Alaska, squelching wildfire expansion and sharply reducing the threat of new fire development, at least for the time being. Areas from the easternmost Seward Peninsula eastward through the central Yukon Valley recorded 2 to 5 inches of precipitation, with the heaviest amounts found along the northern tier of the Koyukuk National Wildlife Refuge and at an isolated site in the central Yukon Valley. Generally 0.5 to 2.0 inches of rain doused most other parts of the state’s western tier, and from the Yukon River through the northern Alaska Range. Most D0 and D1 areas improved in these regions, with moderate drought remaining over the Yukon Flats, where precipitation was less generous. Farther south, light precipitation left dryness and drought unchanged in southern Alaska.

Heavy rains in eastern Puerto Rico removed D0 from most areas, and trimmed areas of moderate drought there. Rainfall was closer to normal over the rest of the Commonwealth, leaving D0 to D2 areas essentially unchanged across central and southwestern areas.

Heavy precipitation brought an end to D0 and D1 conditions across central sections of the Big Island, but conditions were unchanged or deteriorated elsewhere. D0 expanded through the central Hawaiian Island, and parched areas in the extreme northern parts of the Big Island degraded to D3.

Pacific Islands

The weather pattern during this USDM week (7/31/19-8/6/19) was dominated by a monsoon trough across western to central Micronesia and trade-wind disturbances over eastern Micronesia. The monsoon flow and low-level convergence over western Micronesia were enhanced by tropical storms (09W/Francisco, 10W/Lekima) that developed north or northwest of the region, along with a circulation (Invest 95W) that developed over the Marianas late in the week; 95W became a tropical depression (11W) just as the week ended. The monsoon precipitation shifted to the north as the week progressed. In the east, a surface trough interacted with an upper-level trough over Kosrae State and the Marshall Islands (RMI). South of the equator, a surface trough stayed north of the Samoan Islands while a high pressure ridge dominated the weather over American Samoa.

Satellite-based estimates of 7-day precipitation (QPE) showed a large band of 4+ inches of precipitation stretching from west of the Marianas, across Guam and the Marianas, southeastward to Chuuk State, associated with tropical systems and the monsoon trough. Bands of 2+ inches of rain surrounded this area and stretched into Yap State and Palau on the west and Pohnpei State on the east. Areas of 2+ inches of rain could be seen on the QPE over Kosrae State and the RMI. South of the equator, a band of 1-4+ inches of rain was indicated north of the Samoan Islands, but little to no precipitation was seen on the QPE over American Samoa.

Drought free (D-Nothing) conditions persist this week in the Marianas since it was an extremely wet week with all three stations receiving over twice the monthly threshold of 4 inches to meet most water needs in just one week. Saipan had the most rainfall at 11.58 inches, followed by Guam at 10.89 inches and Rota at 10.37 inches.

Palau had 2.50 inches of rain this week, which is more than 2 inches weekly threshold to meet most water needs. Drought free (D-Nothing) conditions continue in Palau.

Most of the FSM had a wet week, with rainfall totals surpassing the 2 inches weekly minimum to meet most water needs. Fananu had the highest rainfall total at 8.93 inches, which is more than four times the weekly threshold. This week Fananu's drought classification was changed from abnormally dry (D0-S) to drought free (D-Nothing) conditions. The rest of FSM was also drought free (D-Nothing). Yap was the only station that had less than the required 2-inches of rain to meet most water needs at 0.54 inch (with 3 days of missing data). However, since the previous week was a wet week, drought free conditions continue in Yap.

Four (Kwajalein, Majuro, Utirik and Wotje) of seven stations in the Marshalls had rainfall totals that surpassed the 2-inch weekly threshold. Wotje had the most rainfall amount at 5.03 inches, leading to a one-category drought improvement from severe drought (D2-SL) to moderate drought (D1-SL). Utirik’s drought was also improved, from extreme drought (D3-SL) to severe drought (D2-SL), as beneficial rains fell this week. Majuro's weekly rainfall total of 4.02 inches helped bring reservoir levels to 78% of the maximum of 36 million gallons, which is close to the critical 80% threshold. For this reason, Majuro's drought classification was also improved from moderate drought (D1-S) to abnormally dry (D0-S) conditions. Although Kwajalein had a wet week (2.34 inches), the last four weeks have been dry. For now, severe drought (D2-S) remains unchanged for Kwajalein. Jaluit (1.54 inches) and Mili (1.44 inches) had rainfall totals that were less than the 2-inches threshold. Their drought status remain unchanged as severe drought (D2-S) for Jaluit and drought free (D-Nothing) for Mili. Ailinglapalap had the least rainfall total at 1.15 inches. Abnormally dry conditions persist for Ailinglapalap.

Pago Pago had 1.28 inches of rain this week, which is 0.72 inch less than the weekly threshold of 2 inches to meet most water needs. The stations located in Siufaga Ridge and Toa Ridge were also dry reporting 0.78 inch and 0.42 inch, respectively. However, because last week was extremely wet for American Samoa, drought free conditions persist.

Virgin Islands

St. Thomas had a very wet week with rainfall totals at Cyril E. King airport at 6.78 inches. Most of that rain fell on July 31 when a total of 4.88 inches was reported at the airport, setting a new record for the highest daily rainfall for this location. The previous record was 1.43 inches set in 2016. Overall, the month of July had a total of 7.75 inches--the wettest July on record for Cyril E. King Airport, surpassing the previous record set in 1958 by 0.34 inches. The year-to-date rainfall total was 18.01 inches or 107.1% of normal precipitation. The SPI value for the 3, 6, and 9 months were 0.94, 0.26, -0.21, respectively, which is consistent with drought free conditions. The SPI value for the 12 months was -0.59 which is consistent with abnormally dry conditions. Drought classification for St. Thomas was improved by one category (from severe to moderate drought) this week due to the beneficial rains.

St. Croix, on the other hand, was dry with only 0.37 inch of rain for the week at the Henry E. Rohlsen. The year-to-date rainfall total was 12.8 inches, which is 73.7% of normal precipitation. SPI values for the 3 and 6 months were 0.08 and -0.17, respectively, consistent with drought free conditions. However, the 9 and 12 months SPI were -0.98 and -1.27, respectively, which is consistent with moderate drought. For this drought week, moderate drought (D1-L) conditions persist in St. Croix.

St. John had a wet week with a weekly rainfall total of 2.43 inches at Windswept Beach, according to data from a volunteer observer. The July rainfall total was 3.62 inches or 106% of normal. Meanwhile, the year-to-date (as of Aug 5) rainfall total was 16.48 inches or 65.5% of normal precipitation. The SPI values for the 6-month period was -0.95, consistent with moderate drought. St. John’s drought classification remained as moderate drought this week.

Looking Ahead

During the next 5 days (August 8 - 13, 2019) should bring heavy rains of 1 to locally 4 inches to portions of western New Mexico, a swath through the central Plains, and many locations across upstate New York and southern Maine. Most of the area from northern Idaho eastward through northern Montana are expecting 1 to 2 inches, as are most of the Dakotas and scattered patches across the Pacific Northwest. Other areas of dryness across the contiguous 48 states should get lesser amounts. Locally up to an inch is expected in the Southeast and southern New England, and little or none is anticipated in most of the new D0 area in the southern Plains from central Kansas through Oklahoma and Texas. Temperatures are forecast to be a few degrees above normal in the southern Plains and the Southeast while subnormal temperatures should extend from the northern half of the Plains to the Pacific Ocean.

The CPC 6-10 day outlook (August 14 -18, 2019) favors above-normal precipitation in east-central Alaska, the Pacific Northwest, the central and northern Plains, the lower Mississippi Valley, and the Southeast. Meanwhile, subnormal precipitation is expected in southern and southeast Alaska, the eastern Great Basin, the Four Corners States, most of Texas, and the Northeast. Temperatures should average below normal from the Intermountain West eastward through the Midwest and Northeast, and across east-central Alaska. Farther south, southern and southeastern Alaska have enhanced chances of warmer than normal weather, along with the Pacific Coast and a large swath from the Great Basin through the Four Corners States, central and southern High Plains, lower Mississippi Valley, and Southeast. The highest likelihood for hotter than normal weather are across most of Texas and the lower Southeast.

Author(s):

Richard Tinker, NOAA/NWS/NCEP/CPC
Ahira Sanchez-Lugo, NOAA/NCEI