May 2015 Drought Report

Overview

The weather and upper-level circulation during May 2015 reflected influences by an El Niño (on central CONUS precipitation) and by a split flow over western North America. The split flow in the upper-level circulation consisted of a long-wave ridge over Alaska and western Canada, and a trough over the southwestern CONUS. The ridge brought warmer- and drier-than-normal weather to Alaska through the Pacific Northwest, while the trough was responsible for cooler- and wetter-than-normal weather over the rest of the West. Aided by an active El Niño, the western trough funneled Gulf of Mexico moisture into the Plains, fueling frequent storm systems which dumped flooding rains over Texas and Oklahoma. A long-wave ridge controlled the weather over the eastern CONUS for much of the month, resulting in a warmer- and drier-than-normal May. As a result, drought and abnormally dry conditions developed and expanded in the drier-than-normal Northeast, as well as Puerto Rico. Drought and abnormally dry conditions contracted in the Great Plains, Upper Midwest, and Central to Southern Rockies where above-normal precipitation fell. May was drier than normal across much of Alaska, with abnormally dry conditions expanding into the southeast panhandle. Beneficial rains fell over drought areas in the Hawaiian Islands, contracting drought slightly. When integrated across the CONUS, May 2015 ranked as the wettest May in the 1895-2015 record, as well as the wettest month ever, due largely to record rainfall in the Plains. On balance, the national drought footprint contracted when compared to last month, plummeting from 31.3 percent of the U.S. as a whole to about 20.6 percent of the U.S. in moderate to exceptional drought, according to USDM statistics. This is the smallest USDM national drought footprint since February 2011. According to the Palmer Drought Index, which goes back to the beginning of the 20^th century, about 16.9 percent of the CONUS was in moderate to extreme drought at the end of May, a decrease of about 8.1 percent compared to last month.

By the end of the month:

• moderate (D1) to severe (D2) drought covered a large part of the western U.S., with extreme (D3) to exceptional (D4) drought extending from California and the Pacific Northwest into the Intermountain Basin;
• pockets of moderate drought developed or expanded in the Northeast, Southeast, and Puerto Rico;
• pockets of moderate drought remained in parts of the Northern and Southern Plains and Upper Midwest; and
• moderate drought persisted in parts of Hawaii.

Percent area of the CONUS in moderate to exceptional drought, January 4, 2000 to present, based on the U.S. Drought Monitor.

Palmer Drought Index

The Palmer drought indices measure the balance between moisture demand (evapotranspiration driven by temperature) and moisture supply (precipitation). The Palmer Z Index depicts moisture conditions for the current month, while the Palmer Hydrological Drought Index (PHDI) and Palmer Drought Severity Index (PDSI) depict the current month's cumulative moisture conditions integrated over the last several months. While both the PDSI and PHDI indices show long-term moisture conditions, the PDSI depicts meteorological drought while the PHDI depicts hydrological drought. The PDSI map shows less severe and extensive drought in parts of the West than the PHDI map because the meteorological conditions that produce drought and wet spell conditions are not as long-lasting as the hydrological impacts.

Used together, the Palmer Z Index and PHDI maps show that short-term dry conditions occurred over much of the eastern CONUS, resulting in expanding or developing long-term drought in May compared to April. The continued short-term wet conditions eliminated long-term drought and expanded long-term wet conditions in the Great Plains to Upper Midwest compared to last month. Short-term wet conditions contracted long-term drought in parts of the interior West, while short-term dry conditions expanded long-term drought along the coastal Northwest.

Standardized Precipitation Index

The Standardized Precipitation Index (SPI) measures moisture supply. The SPI maps here show the spatial extent of anomalously wet and dry areas at time scales ranging from 1 month to 24 months.

The SPI maps illustrate how moisture conditions have varied considerably through time and space over the last two years. Dryness in the Northeast and parts of the Southern Appalachians is evident at all time scales from the last 1 to 12 months. Much of the Ohio Valley and Mid-Atlantic to Southeast is dry at 1 month, but not at the other time scales. Parts of the coastal Northwest are dry at all time scales except 9 to 12 months. Parts of the Northern Rockies are dry at 1 to 6 months. Recent precipitation has neutralized dryness and even indicated wet conditions for much of California and Nevada at 1 to 2 months, but dryness dominates California at the longer (3-24 month) time scales. The recent precipitation has neutralized dryness, or turned conditions wet, in the interior West at all time scales. The heavy rains of the last several months have eliminated dryness across the Southern Plains, and even made conditions appear wet, at all time scales. The recent precipitation has eliminated dryness, or turned conditions wet, in the Northern Plains to Upper Midwest at 1 to 2 months, but dry conditions are still evident at longer time scales, especially the last 6 to 9 months.

Standardized Precipitation Evapotranspiration Index

The SPI measures water supply (precipitation), while the SPEI (Standardized Precipitation Evapotranspiration Index) measures the combination of water supply (precipitation) and water demand (evapotranspiration as computed from temperature). Warmer temperatures tend to increase evapotranspiration, which generally makes droughts more intense.

1-month SPEI for current month.

1-month SPI for current month.

Temperatures were below normal across the Great Plains and much of the West, and much above normal in the Northeast, during May 2015. The warmer-than-normal temperatures amplified the dry conditions in the Northeast when the 1-month SPEI is compared to the SPI. The temperature anomaly pattern is reversed at longer time scales, with western states having record warm temperatures for the last 12 months. This is reflected by more intense drought in California on the 12-month SPEI compared to the SPI. The record wet conditions in the Southern Plains of the last several months (state precipitation ranks for last 1, 3, and 5 months) have neutralized the long-term dryness in Texas and Oklahoma out to the last 36 months as seen on both the SPI and SPEI maps. Last month, the SPI and SPEI maps still showed drought conditions there at the 36-month time scale. Now, drought conditions still show up at the 48-month time scale.

Agricultural, Hydrological, and Meteorological Indices and Impacts

USDA topsoil moisture short to very short

USGS monthly streamflow percentiles

Drought conditions were reflected in numerous agricultural, hydrological, and other meteorological indicators, both observed and modeled.

The dryness of May 2015 was reflected in below-normal precipitation totals, few days with precipitation, and long runs of dry days, especially across parts of California, Arizona, and the Southeast. While April and May rains have improved conditions in the Plains, soils dried out in the East and continued to be parched in the Far West. Vegetation, including crops and pastures and range land, improved with the May rains in the West and Plains, but vegetation showed signs of stress in satellite observations in the East. According to May 31^st reports by the U.S. Department of Agriculture (USDA), only ten percent of the nation's pasture and range land was in poor or very poor condition. As of June 2^nd, only three percent of U.S. corn production was within an area experiencing drought, which is a decrease of 23 percent compared to the end of April. Two percent of soybean production was in drought (a decrease of 20 percent), 12 percent of hay acreage (a drop of 16 percent), 14 percent of cattle inventory (a drop of 22 percent), and 9 percent of winter wheat production (a drop of 35 percent).

The lack of rain in the Northeast, and lack of winter/spring snowpack across most of the West, have resulted in low streamflows in these regions, with many streams recording record low levels. Groundwater levels were low. While reservoirs recovered significantly in Texas, reservoir levels continued well below normal across most western states.

Regional Discussion

Hawaii: Hawaii had a mixed precipitation pattern for May 2015 and for much of the last three years (last 2, 3, 5, 6, 8, 11, 12, 24, and 36 months). But in general, below-normal precipitation has occurred over Oahu and most of The Big Island, while the rainfall pattern has been more mixed over the other islands. On the USDM map, moderate drought shrank to about a fifth (20.12 percent) of the state compared to last month. There were USDA reports of vegetation and pasture stress on Maui early in the month.

Alaska: May was generally drier than normal in the eastern and central portions of Alaska, and wetter than normal along the western and northern coasts, both at the low elevation stations as well as the high elevation (SNOTEL) stations. Many locations in southeastern Alaska had the driest May on record. For most of the time scales in 2015 (last 2, 3, and 5 months), the interior stations have been drier than normal and coastal stations (including the Southeast panhandle) have been wetter than normal. Drier-than-normal conditions spread further to the west and southwest at longer time scales (last 6, 8, 11, and 12 months). The precipitation anomaly pattern is more mixed at the 2- to 3-year time scales. The persistent upper-level circulation pattern (ridge), which is responsible for the drier-than-normal conditions, also brought widespread and persistent above-normal temperatures for much of the last year (last 1, 2, 3, 5, 8, and 12 months). The above-normal temperatures helped reduce the winter snowpack and increase streamflow. The persistently warmer-than-normal temperatures and below-normal precipitation combined to give Alaska the smallest May snow cover extent in the 1966-2015 record. With the snowpack melted out in most areas, small streams that depend on snowmelt are reaching critically low levels and there are concerns that fish migration could be impacted by the end of the month, especially in the southeast, if conditions do not change. Soil moisture models indicated drying soils in the south central and southeast portions of the state. Abnormal dryness expanded to cover about a third (33.9 percent) of the state on the June 2^nd USDM map.

Puerto Rico: May was drier than normal for much of Puerto Rico, especially in the east; only a few areas, mainly in the west, were wetter than normal. The pattern of drier-than-normal conditions in the east and wetter-than-normal conditions in the west persisted throughout the 2014-15 winter (last 2, 3, 5, 6, 8 months). The dryness was reflected in low to record low streamflow in the streams on the eastern half of the island. On the June 2^nd USDM map, abnormal dryness expanded to over a half (55.1 percent) of Puerto Rico, with nearly a third (29.2 percent) in moderate to severe drought.

CONUS State Ranks:

The May precipitation anomaly pattern of dryness in the East and Northeast, and wet conditions in the Plains to Interior West, was reflected in the state ranks, with 17 states ranking in the driest third of the historical record. Six states ranked in the top ten driest category, including Massachusetts which had the second driest May in the 1895-2015 record, Rhode Island (third driest), New Jersey (third driest), Connecticut (fourth driest), Delaware (tenth driest), and South Carolina (tenth driest). Texas and Oklahoma, which had been in a multi-year drought, as well as Colorado had the wettest May on record. For Texas and Oklahoma, May 2015 was the wettest month of any month. Heavy rains which culminated during the last couple months have effectively ended widespread drought in the Southern Plains.

March-May 2015 was drier than normal in the Far West, Northeast, and parts of the Northern Rockies, Northern Plains, and Southeast. Eighteen states ranked in the driest third of the historical record, seven of which had the tenth driest, or drier, spring. These included Connecticut (which ranked fourth driest), Massachusetts (fourth driest), New Hampshire (fifth driest), New York (ninth driest), California (ninth driest), Rhode Island (tenth driest), and Vermont (tenth driest). The last three springs, and six of the last nine springs, have been much drier than normal in California. Three of the last four springs have been much drier than normal in Connecticut.

The precipitation anomaly patterns for the last five to six months were similar. Both had dryness in the Far West, Northeast, Northern Plains to Midwest, and parts of the Southeast, except the year-to-date pattern of dryness was more severe. Seventeen states ranked in the driest third of the historical record for January-May 2015, while 14 ranked in the driest third of the historical record for December 2014-May 2015. Eight states ranked in the top ten driest category for year-to-date, including Connecticut (second driest), New York (third driest), California (fifth driest), New Hampshire (sixth driest), Massachusetts (ninth driest), and Pennsylvania, Rhode Island, and Vermont (each tenth driest). Two states (Connecticut and New York) had the tenth driest, or drier, December-May. Eleven of the last 15 January-May periods in California have been drier than the long-term average, with the last three being exceedingly dry.

The above-normal precipitation pattern in the central part of the CONUS for the last several months dominates the precipitation anomaly pattern at the 12-month time scale. Eight states — two along the West Coast, five in the Northeast, and one in the Southeast — ranked in the driest third of the historical record for June 2014-May 2015. Connecticut had the eleventh driest June-May. In California, May 2015 and December and the summer months of 2014 were wetter than normal across much of the state, but the last 12 months still ranked as the 29^th driest June-May in the 1895-2015 record, statewide, in spite of those wet months. Ten of the last 15 years (June-May periods) have been much drier than normal in the state. The persistent record warmth of the last three years has combined with the extreme dryness to produce a record dry 36-month SPEI for California.

Western U.S.

As noted above, dry weather has dominated the West for much of the last three to four years, resulting in significant hydrological (low lake, reservoir, and stream levels) and agricultural impacts. Recent precipitation has helped alleviate some of the short-term impacts, but long-term drought impacts remain. According to the USDM, 57.0 percent of the West was experiencing moderate to exceptional drought at the end of May, which is a decrease of about 5.1 percent compared to the previous month. The Palmer Drought Index percent area statistic for the West was 44.4 percent, a decrease of about 20.8 percent compared to the previous month.

Agricultural Belts

Primary Corn and Soybean Belt precipitation, May, 1895-2015.

Primary Corn and Soybean Belt precipitation, March-May, 1895-2015.

March serves as the beginning of the growing season for the Primary Corn and Soybean agricultural belt. The region was generally wetter than normal this month, with May 2015 ranking as the 17^th wettest and 40^th warmest May on record, regionwide. The growing season to date ranked as the 37^th wettest and 25^th warmest March-May on record, regionwide.

October marks the start of the growing season for the Primary Hard Red Winter Wheat agricultural belt; by May the growing season is generally over. The region was much wetter than normal this month, with May 2015 ranking as the wettest and 21^st coolest May in the 1895-2015 record, regionwide. The growing season ended up as the tenth wettest and 26^th warmest October-May in the 120-year record. According to the USDA, the portion of the U.S. winter wheat crop in drought fell sharply from 44 to 9 percent between April 28^th and June 2^nd. However, May rainfall arrived too late to reverse the impacts of a harsh winter, leaving roughly one-third of the crop in very poor to poor condition by May 31^st in South Dakota (37%), Nebraska (32%), and Kansas (29%).

NOAA Regional Climate Centers:

A more detailed drought discussion, provided by the NOAA Regional Climate Centers and others, can be found below.

Southeast — South — Midwest — Northeast — High Plains
West

As described by the High Plains Regional Climate Center, it was a cool and extremely wet month for the High Plains region. Widespread heavy rainfall in excess of 200 percent of normal not only led to the reduction or removal of drought conditions, but in many cases, to extensive flooding. South Dakota went from having its driest start to any year (January through April) to having its 7th wettest May on record. The heavy rain has not just impacted roadways and buildings, but has also caused problems for producers as planting and haying activities have been delayed in several areas due to wet field conditions. The excessively wet conditions have also allowed for an increase in insect and disease issues for crops, especially in Kansas, Nebraska, and South Dakota. Leaf rust, stripe rust, and head scab in wheat have been the major issues. Additionally, fertilizer applications have been disrupted or even lost due to the heavy rains.

The heavy precipitation greatly improved drought conditions this month, according to the USDM. The total area in drought (D1-D4) across the High Plains region decreased from about 44 percent to just under 7 percent. South Dakota and Kansas experienced the largest changes over the past month, decreasing their drought coverage area by 68 percent and 62 percent, respectively. All extreme drought conditions (D3) have been erased from the region and only a small area of severe drought (D2) remains in eastern South Dakota. Colorado, Kansas, Nebraska, and Wyoming have some areas of abnormally dry (D0) or moderate drought conditions (D1) remaining, while North Dakota is now drought free, with areas of D0 in the east and west. The only areas to degrade included small areas of western North Dakota and northwestern Wyoming, where D0 developed. It is worth noting that in some areas of drought recovery, some lingering drought impacts remain.

As explained by the Southern Regional Climate Center, May average temperatures in the Southern region varied west to east. Western counties in Texas and Oklahoma experienced a cooler than normal month, while eastern counties, particularly in Tennessee and Mississippi, experienced a warmer than normal month. With the exception of Tennessee, May was an extremely wet month across the Southern region, with historically high precipitation totals at both the station and state level. The wettest portions on the region included most of southern Oklahoma and northern Texas, where stations saw as much as 28 inches (711.2 mm) of rainfall for the month. In the South Central Climate Division of Oklahoma, several stations reported over 20 inches (508.0 mm) for the month. Similarly, stations in the North Central Climate Division of Texas consistently reported well over 10-11 inches (254.0-279.4 mm). The state-wide value of 8.93 inches (226.82 mm) for Texas was not only the wettest May on record, but it was also the wettest month ever, eclipsing the previous value of 6.66 inches (169.16 mm) set back in June of 2004. The state-wide average for Oklahoma was also the wettest month ever. Putting this rainfall in perspective, the Southern region averaged over eight inches (203.2 mm) of rain; that's the equivalent of an ankle deep pool of water spread over an area just over half a million square miles (1,294,994 square km).

The historic May rainfall totals in Oklahoma and Texas have resulted in a tremendous improvement of drought conditions in both states. As of June 2, 2015, only 0.32 percent of the Southern region is in drought, with no states showing any severe (D2), extreme (D3) or exceptional (D4) drought conditions. The May 19th USDM marked the first time since June 22, 2010 that there was no extreme or exceptional drought in the Southern region. It was also the first time since November 23, 2010 for Texas, and the first time since March 8, 2011 for Oklahoma, that the drought map for each state was not showing any D3/D4 drought.

In Texas, state reservoirs now stand at 83.3% full which is a 10% jump since the start of the month. Dallas-area reservoirs increased from 64% of capacity in March to more than 95% of capacity. Wichita Falls ended the month under a Stage 2 water restriction, having started under Stage 5 Drought Catastrophe. Not all of the state saw the same improvements, however, as both Abilene and San Angelo are sitting at near record low reservoir storage — 12 and 22 percent of capacity, respectively. Agriculturally, the flooding that has occurred across multiple parts of the state has washed out a lot of crops. In the Rio Grande Valley, some farmers are saying that their entire summer batch of squash has been washed completely out. This problem stretches all across the state since flooding has been a big issue throughout the month. Other crops that are still being planted, such as cotton, are behind schedule due to the extreme rainfall and saturation of soils across the state; cotton planting is 10 percent behind the last several years' average. Despite the problems with saturated topsoil, the recent rains did much to ease the subsoil moisture loss from the last several years, as now only 5% of croplands are short or very short. Ecologically, cattle have an abundance of water from the rains, and pastures and rangeland improved such that only 5% are poor or very poor and 72% are good or excellent (Information provided by the Texas Office of State Climatology).

As summarized by the Midwest Regional Climate Center, the southeast portion of the Midwest region saw rainfall of zero to four inches (0-102 mm) below normal, while the remaining part of the region except for some isolated areas in Iowa, southeast Wisconsin, and the thumb of Michigan saw rainfall two to four inches (51-102 mm) above normal. The split weather pattern of drier and warmer weather in the northwest part of the Midwest region and wetter weather across the southeast portion of the region in late April and early May allowed many farmers across the northwest states to get into the fields earlier than average and complete planting. Much of the region was above the 5-year average for corn planting. Minnesota and Wisconsin were the states to benefit the most form the drier and warmer weather pattern before heavier rain events came later in May, having 100 percent and 85 percent of the crop planted across the states, respectively, by the week ending on May 17th, 2015. This was roughly 60 to 70 percent greater than the 5-year average. The wetter conditions in the southeast portion of the region delayed planting some, but all states remained ahead of the 5-year average planting dates. Soybean planting in Minnesota was also much ahead of schedule, with 88 percent of the crop planted, with the 5-year average of 59 percent by this time of year. Remaining states had 60 to 76 percent of soybeans planted by May 26th, with Missouri only at 20 percent planted. A wetter period from May 8th -21st brought some much needed rainfall to Minnesota, downgrading moderate drought conditions to abnormally dry conditions in much of Minnesota and Wisconsin according to the USDM.

As noted by the Southeast Regional Climate Center, mean temperatures in May were slightly above average across much of the Southeast region, and precipitation was generally below normal, with isolated pockets of wetness in some locations. The driest locations were found across Virginia, central portions of the Carolinas, coastal Georgia, and eastern Florida. Monthly precipitation totals in these areas were 2 to 4 inches (50.8 to 101.6 mm) below normal, or 50 to as little as 5 percent of normal. Charlotte, NC (1879-2015) and Moultrie, GA (1926-2015) observed their third driest May on record with only 0.32 (8.1 mm) and 0.46 inch (11.7 mm) of precipitation, respectively. In addition, only one day of measurable precipitation was recorded in Charlotte during the month, which ties for the fewest number of days during May with measurable precipitation at this location.

Mean temperatures were above average in Puerto Rico and the U.S. Virgin Islands. Both Guayama, PR (1914-2015) and Juncos, PR (1931-2015) observed their warmest mean temperature for May on record. Precipitation was below normal for much of Puerto Rico and the U.S. Virgin Islands during May. Guayama, PR observed its driest May on record with only 0.27 inch (6.9 mm) of precipitation, and Juncos, PR observed its second driest May on record with 1.01 inches (25.7 mm) of precipitation.

A modest change in drought conditions was observed across the region during May. The percentage of the region under drought-free conditions (less than D1) decreased slightly from approximately 99 percent on May 5th to 98 percent on May 26th. Moderate (D1) drought conditions expanded across far southern Florida, and a small area of moderate drought developed near Valdosta in south-central Georgia. The unusually warm and dry conditions during May contributed to numerous agricultural impacts throughout the region. Peanut planting in Georgia was aided by dry conditions at the beginning of the month, but recent dryness prevented any significant growth in the crop. Despite a late frost across southern Georgia in late March, the persistent warmth during May helped the peach crop develop quickly, leading to a favorable harvest of small but sweet fruit.

As explained by the Northeast Regional Climate Center, May was an extremely mild month for the Northeast with well below-normal precipitation. The region's average temperature of 61.6 degrees F (16.4 degrees C) was 5.4 degrees F (3.0 degrees C) above normal, making it the warmest May since record-keeping began. The region received 2.42 inches (61.47 mm), 59 percent of normal, making it the 15th driest May on record. At the beginning of May, 50 percent of the Northeast was abnormally dry. A continuing lack of precipitation and extremely low stream flows contributed to moderate drought being introduced in parts of the region in the USDM issued on May 21. By month's end, 47 percent of the region was abnormally dry, while 24 percent of the region was experiencing moderate drought conditions. USDA crop reports indicated that plant growth was slow due to lack of moisture, with some farmers already irrigating and other farmers delaying planting until rain fell. Dry conditions also contributed to numerous wildfires across the region, including a fire that burned around 2,600 acres in Sullivan and Ulster counties in New York.

As summarized by the Western Regional Climate Center, the West saw a transition to a more active atmospheric pattern this month. Several slow-moving low-pressure systems passed through the region bringing widespread above normal precipitation to the Great Basin, Desert Southwest, and the Central and Southern Rocky Mountain states. Below normal temperatures accompanied the storminess. The Pacific Northwest saw above normal temperatures this month. Over two feet of late season snow fell in the high Sierra Nevada during the month, providing a small addition to the nearly non-existent snowpack. Precipitation in these areas increased soil moisture, reduced irrigation demands, and supported vegetation growth. However, it did not reduce the persistent hydrologic drought in California, Nevada, and southern Oregon. The precipitation helped to ameliorate drought conditions across a large area of the Colorado-Utah-Wyoming borders, and along the eastern part of the Colorado-New Mexico border. Precipitation was below normal along the Pacific Coast west of the Sierra and Cascades from Los Angeles to the Canadian border and along the northern tier of the West.

Despite above normal May precipitation, drought conditions remain in California/Nevada/Oregon. Impacts include low spring runoff threatening fisheries and water resources, curtailment of water deliveries for agriculture, mandatory water restrictions in California, and ecological impacts on forests and wildlife. Due to low snowpack, wildfire hazards, crop losses, and threats to wildlife, Washington Governor Jay Inslee declared a statewide drought emergency on May 15.

May marked the end of Alaska's main snow season and end of the least snowy season on record for Anchorage, where only 25.1 in (63 cm) of snow fell September through May. The previous lowest snowfall was 30.4 in (77 cm) in 1957-58 and normal is 74.5 in (189 cm). Several locations throughout Alaska observed their warmest May on record this month including Juneau in the southeast (54.1 F/12.3 C) and Kotzebue (40.3 F/4.6 C) in the northwestern part of the state. Records for Juneau began in 1936 and for Kotzebue in 1897. Further south, as Hawaii moved into its dry season this month, precipitation was variable across the state. Kahului received 2.23 in (57 mm), 300% of normal and the 8th wettest May since records began in 1905. In contrast, Honolulu recorded only 0.2 in (5 mm), 32% of normal.

Pacific Islands: According to reports from National Weather Service offices, the Pacific ENSO Applications Climate Center (PEAC), and partners, conditions varied across the Pacific Islands.

In the U.S. Affiliated Pacific Islands (maps — Micronesia, Marshall Islands, basinwide), May 2015 was drier than normal in the Republic of Palau and parts of eastern Micronesia, and wetter than normal in the Mariana and Marshall Islands and American Samoa. May is in the dry season for the northern and western stations (Koror, Yap, Guam, and Saipan).

Above-normal May rainfall was reported by stations in the Republic of the Marshall Islands, Mariana Islands, some stations in Micronesia, and American Samoa, including Guam, Saipan, Yap, Pohnpei, Kapingamarangi, Kwajalein, Majuro, and Pago Pago. Rainfall was below normal at Koror, Chuuk, Lukonor, and Kosrae. May is in the wet season for Chuuk, Lukonor, and Kosrae, so normals are high.

El Niño dryness caused rainfall amounts to be below the minimum thresholds (4 or 8 inches) required to meet most monthly water needs at stations in the Republic of Palau and western Micronesia. May rainfall amounts were also below minimum thresholds at stations in the Republic of the Marshall Islands. These included Koror, Woleai, Jaluit, Utirik, and Wotje. The 4- and 8-inch thresholds are important because, if monthly precipitation falls below the threshold, then drought becomes a concern. Koror was below the 8-inch threshold for the fifth consecutive month, and seven of the last eight months have been drier than 8 inches. The National Weather Service issued a Drought Information Statement for the Republic of Palau warning of increasingly dry weather across Palau and western Micronesia due to the ongoing El Niño. The Statement emphasizes the need to monitor water supplies and food crops and to conserve water.

As measured by percent of normal precipitation, Koror and Kosrae were drier than normal in both the short term (May and the last 3 months [March-May 2015]), the year to date [January-May 2015]), and the long term (12-month time scale, June 2014-May 2015). Lukonor was wetter than normal for the year-to-date, but otherwise drier than normal. Chuuk, Guam, Kapingamarangi, Kwajalein, Majuro, Pago Pago, Pohnpei, Saipan, and Yap were wetter than normal at both the short- and long-term time scales and year-to-date.

SPI values for seven time periods for Pacific Islands, computed by the Honolulu NWS office.

For additional, or more localized, drought information, please visit:

• The U.S. Drought Portal
• National, Regional, and State Drought Resources