Hurricane Helene dropped heavy to excessive amounts of rain on a large area from the Ohio Valley, central Appalachians, and mid-Atlantic Piedmont southward to the eastern Gulf Coast region.
The storm moved inland across the Florida Panhandle and northward into the South Atlantic States, then slowed down and drifted westward as it interacted with an upper-level low pressure system, becoming quasi-stationary as it slowly dissipated.
The heaviest rains fell where precipitation was orographically enhanced on the east side of the Appalachians. Part of the central North Carolina mountains received 20 to almost 30 inches of rain, with totals topping 10 inches over the rest of the North Carolina mountains. Similar recordings were in central Blue Ridge in Virginia, part of central and western South Carolina, some patches in central Georgia, and near the landfall site. More than 4 inches soaked a broad area from the middle and lower Ohio Valley southward through eastern Alabama and eastward through the central and southern Appalachians and Piedmont, including most of the Carolinas and Georgia.
Widespread flooding resulted, with devastating floods impacting the wetter areas, along with prolonged power outages. Helene is the deadliest tropical system to affect the Nation since Hurricane Katrina in 2005, with a death total was approaching 200 as of this writing. At the same time, the intense rains dramatically improved or ended the various degrees of dryness and drought that had been affecting many of the areas impacted by Helene. This was true especially from the Appalachians westward through the Ohio and Tennessee Valleys and southward to the central Gulf Coast, in addition to much of South Carolina and northern Georgia.
Outside the broad area impacted by Helene, subnormal precipitation prevailed across most of the contiguous states. Precipitation was almost non-existent over a large area from the western Great Lakes and most of the Mississippi Valley westward to the Pacific Coast. A few sites in the northern Intermountain West and areas from the northern Cascades to the Pacific Coast receiving over one-tenth of an inch. Above-normal temperatures accompanied the low precipitation totals, resulting in dryness and drought persisting or intensifying across this area covering a majority of the contiguous states.
The U.S. Drought Monitor is jointly produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the U.S. Department of Agriculture and the National Oceanic Atmospheric Administration. (Map courtesy of NDMC.)
South
Intense rains spawned by Helene dropped 2 to locally 6 inches of rain on Tennessee and northeastern Arkansas, but lesser amounts fell elsewhere. A few tenths of an inch of rain (with isolated higher amounts) fell on parts of eastern Texas and Oklahoma and scattered portions of Louisiana, Mississippi, and the remainder of Arkansas. Other locations recorded little or no rain.
Predictably, the heavy rains across Tennessee led to broad-scale reductions in the areal coverage dryness and drought, leaving only south-central parts of the state in drought. Improvements were also indicated in northern Mississippi and eastern Arkansas, where a re-assessment of conditions demonstrated that early September rainfall from Hurricane Francine was more beneficial than initially thought.
Meanwhile, D0 was expanded across southern Louisiana, and areas of deterioration were identified in Texas and Oklahoma, including an expansion of exceptional drought in the Texas Big Bend, and increased coverage of severe to extreme drought in portions of Oklahoma. Rainfall during the past 60 days was less than half of normal in portions of northeastern Oklahoma, the Red River Valley, eastern Texas, and the Texas Big Bend. According to the U.S. Department of Agriculture, half of the Texas cotton crop was in poor or very poor condition, along with 31% of Texas corn and 24% of Oklahoma cotton.
Midwest
Most locations from southeastern Missouri received 0.5 to 2 inches of rain with isolated higher amounts, especially in Missouri near the Ohio/Mississippi Rivers’ confluence. In sharp contrast, little or no rain fell on the western tier of the Midwest Region from most of Missouri northward through Iowa, Minnesota, and Wisconsin. This highly variable rainfall pattern affected dryness and drought predictably, with conditions improving along most of the southern tier of the Midwest Region while dryness and drought was unchanged or intensified along the western tier of Midwestern states. In areas unaffected by Helene, severe drought expanded to cover a larger part of southwestern Missouri.
Meanwhile, D0 and D1 conditions expanded substantially in the rest of Minnesota, and to a lesser extent Iowa. Accumulated precipitation over the past 60 days is above normal across parts of southeastern Missouri while totals are 3 to 6 inches below normal in southern Minnesota, most of Iowa and most of northern and western Missouri. Over northern Minnesota, the west half of Iowa, and part of western Missouri, these totals were near or less than half of normal. The lack of rain is significantly impacting livestock and some field drops across southwestern Missouri and adjacent areas.
High Plains
It was very warm and almost bone dry throughout the region, with only a few highly isolated spots of measurable rainfall. Unusually high temperatures worsened the situation, with weekly mean anomalies ranging from +1 to +2 degrees Fahrenheit in eastern Kansas to +15 to +18 degrees in most of the Dakotas. Wyoming and most of Colorado saw temperatures average near or over 10 degrees above normal.
As a result, dryness and drought in the region was unchanged or worsened. Moderate to severe drought expanded in coverage across the central Great Plains and northern High Plains, with increased areas of extreme drought D3) noted in eastern Wyoming, plus a few spots in the western Dakotas. Over the past 30 days, only a few tenths of an inch of rain at most has fallen on much of Wyoming and Nebraska, northern Kansas, and the southeastern Dakotas.
West
Some of the higher elevations recorded a few tenths of an inch in portions of northern Idaho and northwestern Montana. However, most of the West was very warm and free from any measurable precipitation. A few areas in Utah saw conditions noticeably deteriorate this past week, but no other degradations took place.
Some D0 and D1 areas were actually scaled back in central and northwestern Montana despite the warm and dry week due to a few rounds of heavy precipitation in late August and September, which has continued to have a positive impact on soil moisture, vegetative health, and 1- to 4-month precipitation anomalies. Elsewhere, conditions are unchanged from last week.
Low relative humidity, high temperatures, and gusty winds continue to produce periods of extreme fire danger, and supplemental feeding and watering of livestock has been common in eastern Montana. With the Southwest monsoon season ending and the wet season in the West not yet underway, drought tends to progress slowly in the region this time of year.
Looking ahead
During the next five days, Oct. 3 to 7, warm and dry weather will dominate the contiguous United States. Very little if any precipitation is expected across a vast majority of the nation. The Florida Peninsula the immediate rim of the Gulf Coast are significant exceptions, where abundant tropical moisture is expected to feed heavy rainfall. There is some potential for tropical cyclone development over the Gulf later in the period.
Over an inch is forecast across the Florida Peninsula and along parts of the immediate Gulf Coast from the Florida Panhandle through coastal southern Texas. Moderate amounts (0.5 to 1.5 inches) are forecast over parts of northern Idaho and adjacent Montana. Near normal temperatures are expected in most areas east of the Mississippi River while well above-normal temperatures should prevail farther west. Daily maximum temperatures 10 to 15 degrees above normal are predicted from the central and northern Plains through most of the Rockies and Intermountain West to near the California Coast.
The Climate Prediction Center’s 6- to 10-day outlook, Oct. 8 to 12, continues to favor warmer and drier than normal weather for most of the nation. A much larger area with increased chances for drier-than normal weather stretch across the northern Rockies and from the High Plains eastward through the southern and middle Atlantic Coast. Meanwhile, warmer than normal weather is expected from the Great Lakes and the Mississippi Valley westward to the Pacific Coast, with odds for unusual warmth exceeding 80% over northern and central sections of the Rockies and Plains.
Richard Tinker is with National Oceanic Atmospheric Administration, National Weather Service, National Centers for Environmental Prediction and Climate Prediction Center.
