Event Summary      National Weather Service, Raleigh NC

Hurricane Ivan, September 2004 Updated 2014/01/16 (Click on the image to enlarge.) Event Headlines ...Hurricane Ivan was the 9th named tropical cyclone of the 2004 Atlantic hurricane season... ...6 of the 9 named tropical cyclones have impacted North Carolina... ...Rain bands associated with Ivan produced several tornadoes over the Piedmont of North Carolina. One tornado hit Stokesdale in northwestern Guilford County followed by several more touchdowns in Rockingham County, Moore County, and Chatham County... ...A strong down burst, associated with a convective rain band, hit the Raleigh-Durham International Airport producing a wind gust of 79 MPH. This down burst produced significant damage to a terminal and flipped several small planes. This was the second strongest wind gust recorded at the airport, trailing only the 90 MPH gust on October 15, 1954 associated with Hurricane Hazel... ...A swath of 3 to 6 inches of rain fell across the North Carolina Mountains associated with Ivan. There were reports of 7 to 10 inches of rain along the higher terrain with isolated reports in excess of 11 inches... ...Severe flooding and damage resulted in many Mountain counties including a major land slide near Franklin in Macon County... ...Several fatalities in North Carolina were directly related to the storm... Overview Tropical Depression Ivan developed late in the afternoon on Thursday, September 2, 2004, 550 miles southwest of the Cape Verde Islands. Ivan became a Tropical Storm early on Saturday, September 4, 2004, approximately 1600 miles east-southeast of the Lesser Antilles. Ivan was moving west at 18 MPH. Ivan became the 5th Hurricane of the 2004 Atlantic season at around 500 AM, Sunday, September 5, 2004, 1200 miles east-southeast of the Lesser Antilles. Ivan's maximum sustained winds had increased to 75 MPH, with a minimum pressure of 987 MB. Ivan strengthened into the fourth major Hurricane of the 2004 Atlantic at 100 PM, Sunday, September 5, 2004. Ivan had maximum sustained winds of 115 MPH, while located 995 miles east of the Windward Islands. From September 7 through September 13, Hurricane Ivan maintained at least category 4 intensity during its journey across the central Atlantic into the Caribbean. Ivan reached Category 5 intensity on several occasions during this period. Along its general west-northwest course, Ivan affected Grenada, the Windward Islands, Jamaica, the Cayman Islands, and the western part of Cuba before moving turning to the north and reaching the Gulf of Mexico late on September 13, 2004. Ivan gradually turned toward the north as it moved through the Gulf of Mexico on September 14 and 15, 2004. It maintained a Category 4 status during the few days proceeding land fall. Ivan decreased slightly in intensity, to a strong Category 3 storm, just before making land fall. The center of Hurricane Ivan moved on shore near Gulf Shores, Alabama, at around 300 AM on Thursday, September 16, 2004. maximum sustained winds at landfall were estimated to be near 130 MPH, with a minimum pressure of 943 millibars. Ivan weakened rapidly as it moved north and then northeast across Alabama on Thursday. Ivan was downgraded to a Tropical Storm at 200 PM on Thursday, when it was located 45 miles west-northwest of Montgomery, Alabama. Maximum sustained winds had decreased to 70 MPH and the pressure had come up to 975 MB. The tropical storm was downgraded to a Tropical Depression late on Thursday evening while centered 25 miles to the north-northwest of Gadsden, Alabama. Maximum sustained winds had dropped to near 35 mph with a minimum pressure of 986 MB. At this time, widespread heavy rain affected much of the southern Appalachians. The system remained a Tropical Depression status as it slowly moved northeast across northwestern Georgia and eastern Tennessee during Thursday night and Friday morning. By 1100 AM, Friday, September 17, the depression was located 45 miles east of Knoxville, Tennessee. Widespread heavy rain affected western North Carolina Thursday night and Friday. Wind gusts reached between 40 and 60 MPH across the higher elevations of the Appalachians. Numerous trees were downed and flooding was widespread. Rainfall amounts reached 8 to 12 inches across portions of the higher elevations. As the depression moved across northeastern Tennessee and southwestern Virginia Friday afternoon, the Piedmont of North Carolina remained in the warm sector of the storm. As late morning and afternoon temperatures reached the 80s, several rain bands became enhanced and produced damaging winds and several tornadoes. Tornadoes, varying in intensity from F0 to F2, touched down producing damage to homes, businesses, and trees in Guilford, Rockingham, Moore, and Chatham Counties. Damaging winds were reported with several of the rain bands including a 79 MPH wind gust at the Raleigh-Durham Airport. This was the second strongest wind gust ever recorded at the airport. The strongest wind gust occurred on October 15, 1954 when Hurricane Hazel produced a gust to 90 MPH. Additional Details Additional details may become available at the NWS offices directly affected by the storm... The National Weather Service Greenville/Spartanburg The National Weather Service Blacksburg

Ivan's Track Hurricane Ivan Track Hurricane Ivan followed a west-northwest course at about 10 mph on Saturday and Sunday (September 11th and 12th) as it approached the Yucatan Channel. Ivan made a gradual turn toward the northwest and then north on Monday and Tuesday (September 13th and 14th). On Wednesday, September 15th, Ivan turned more northerly as it approached the Gulf Coast. After making landfall, Ivan's track turn more northeasterly as it moved across the Deep South and Appalachians. Hurricane Ivan Track (Click on the image to enlarge.) Detailed Hurricane Ivan Track (Click on the image to enlarge.)

Maps of Precipitation Totals, Maximum Wind Gusts, and Severe Weather Reports from Hurricane Ivan Precipitation Totals from Hurricane Ivan The map below contains precipitation totals during the period in which Ivan impacted North Carolina (from 800 AM EDT on Thursday, September 16 through 800 AM EDT on Sunday, September 19). Note the large area of rainfall of 4 to 8 inches across much of western North Carolina. Some of the higher elevations received 8 or more inches of rain. Much of this heavy rain fell in locations that experienced heavy rain from the remnants of Hurricane Frances a week earlier. The maximum of heavy rain across the northern Piedmont of North Carolina was largely due to a band of thunderstorms associated with Ivan that swept across the state on Friday afternoon. Maximum Wind Gusts from Hurricane Ivan The map below contains the maximum wind gusts from the remnants of Hurricane Ivan as it moved across North Carolina. All of the wind gust reports shown below were observed on September 17, 2004. The map shows that much of North Carolina experienced wind gusts of at least 30 MPH. The wind gusts across the Mountains and Foothills were generally associated with the circulation center of the remnants of Ivan as it moved across the Appalachians. Wind gusts across the Piedmont and Coastal region were often influenced by convective rain bands associated with the remnants of Ivan and mixing resulting from the breaks periods of sunshine that developed well to southeast of Ivan. There were a few isolated wind gusts approaching or exceeding 50 MPH in the Piedmont and Sandhills region (79 MPH at Raleigh-Durham, 51 MPH at Burlington and 47 MPH at Fayetteville.) Severe Weather reports from Hurricane Ivan The map below contains severe weather reports received by the National Weather Service during the period in which Ivan impacted North Carolina (from 800 AM EDT on Thursday, September 16 through 800 AM EDT on Sunday, September 19). The number of reports of flooding and wind damage received across the mountains were so numerous that the letters marking the particular severe weather report are approximate. The location of the severe weather reports noted across the Foothills and Piedmont should be accurate.

Severe Weather Potential There were several convective parameters observed in the 12Z Greensboro (KGSO) sounding that indicated an environment favorable for tornadoes. Analysis using the "Sounding Toolkit" indicated that the 0-3 km storm-relative helicity was over 300 m2/s2 (critical value 250), and the 0-1 km SRH was 239 (critical value 100). The SPC mesoanalysis of helicity at 18Z showed the axis of highest helicity was located over the Piedmont. The LCL was also quite low, around 650 m AGL (critical value 1000). The VGP (vorticity generation parameter) was 0.43 (critical value 0.2), and the EHI (energy helicity index) was 3.9 (critical value 1). As a result, a tornado watch was issued for all of central NC at 1016 am. Overcast cloud cover in the morning diminished with skies becoming broken by midday in the eastern half of central NC, allowing surface heating to destabilize the atmosphere and create a differential heating boundary in the western Piedmont. It was primarily along and on the cool side of this boundary that the tornadoes formed. Once the rain bands were east of this boundary, the primary mode of convection evolved from tornadic supercells to bow echoes. The SPC mesoanalysis of temperature and dewpoint and CAPE show the presence of this boundary at 18Z. The 18Z sounding from MHX may also have been indicating a change from tornadic storms to straight-line wind damage. Certainly, the VWP plotting tool on AWIPS demonstrated a clear change from a strongly veering wind profile in the lowest one or two thousand feet to little wind direction change with height between 17Z and 21Z. In the east, the CAPE was very high (>3600 J/kg), and the helicity values were lower (0-3 helicity was 112 m2/s2). The theta-E difference between the minimum theta-E in the sounding and the maximum theta-E in the lowest 300 mb (TE Diff_300mb in Sounding Toolkit) was 34.8 C (critical value 20), indicating a high potential for damaging downburst winds. Analyzed mean sea level pressure (black) and surface wind barbs from SPC at 18Z on Friday, September 17, 2004 (2 PM EDT). The circulation center is located across the North Carolina mountains. Analyzed surface temperatures (red), dewpoints (green), and wind barbs from SPC at 18Z on Friday, September 17, 2004 (2 PM EDT). Note the temperatures in the lower to mid 80s with dewpoints in the lower to mid 70s across central and eastern North Carolina. Analyzed precipitable water (green) and wind barbs from SPC at 18Z on Friday, September 17, 2004 (2 PM EDT). Note that much of North Carolina has precipitable water values of 1.8 inches or greater. 0-3 Km Storm Relative Helicity (blue) and storm motion (brown) from SPC at 18Z on Friday, September 17, 2004 (2 PM EDT). Note the axis of Storm Relative Helicity values greater than 250 across central North Carolina with maximum values greater than 350. Surface based CAPE values from SPC at 18Z on Friday, September 17, 2004 (2 PM EDT). Note the area of high CAPE across central and eastern North Carolina.

Stokesdale Tornado Two outer bands for the remnants of Hurricane Ivan spawned multiple tornadoes, wind damage and heavy rains across the Piedmont during the late morning and afternoon hours of Friday September 17th. The worst tornado damage occurred in northwest Guilford County around Stokesdale where a tornado touched down about 1110 am ( storm relative velocity image from the krax WSR-88D at 1107 AM and base reflectivity image from the krax WSR-88D at 1107 AM ). The tornado tracked north for at least 7 miles through Guilford County then tracked a few more miles north into Rockingham county. The average tornado intensity was F1 with wind between 73-112 mph. Working with Guilford County Emergency Management, the initial tornado touchdown was identified in northwestern Guilford County near the intersection of Harrell Road and Lee's Glen Road. The tornado intensity at this point was F1 with winds around 75 mph. Damage in this area was light with roofs blown off 3 garages and numerous trees snapped or uprooted. Winds in the tornado intensified some as it tracked north across Meadows Drive and Haw Meadows drive where falling trees caused significant damage to at least 3 well built homes. One home was a total loss. By the time the tornado reached Prince Edward Road wind speeds were likely around 90 mph, resulting in the snapping or downing of about 70 percent of the trees in a heavily wooded area. Structures in this area were likely spared significant damage due to the dense forest helping to break the wind near the ground. At Kelly Court a trampoline pole was driven through the wall of a home and a 2 car garage was destroyed due the failure of the garage door. Winds in this area were also around 80 to 90 mph based on damage. At South Point Drive just northwest of downtown Stokesdale the roof was blown of a house resulting in major damage to the structure. Winds in this area were between 100-110 mph, in the upper range of F1. Neighboring houses suffered much less damage including the loss of shingles, siding and porches. The tornado missed Stokesdale Elementary by a little less than a mile. Just across the county line a double wide trailer was destroyed in Rockingham County as the tornado continued north. See the latest storm damage assessment issued by the Blacksburg National Weather Service office. No injuries or fatalities occurred in this tornado. Many people reported hearing the Tornado Warnings, took cover as the tornado hit or were away at work. An F1 tornado contains winds of 73-112 mph which will peel surfaces off roofs, shatter windows, overturn trailers, uproot trees and even move automobiles. Stokesdale Tornado Track (Click on the image to enlarge.)

79 MPH Wind Gust at Raleigh-Durham International Airport The national Weather Service surveyed damage from severe thunderstorms that impacted Raleigh-Durham International Airport just before 400 PM Friday, September 17, 2004. All indications were that the damage was a result of straight line winds of around 80 mph. The observation from the airport at 353 PM showed winds of 69 knots, or 79 mph ( base reflectivity image from the krax WSR-88D at 351 PM ). Although there were reports of funnel clouds around the time of the storms passage across the airport, no confirmation of a tornado could be obtained from a survey of the damage, which included blown out windows and small planes moved or flipped over.

Warning Decision Process The first band to affect the area approached from the southwest. It contained mainly light to moderate rain as it moved northeast out of northern SC and the Charlotte area. As the band moved into the Triad, several storms within the band increased in intensity. While the entire band was moving east-northeast, the cells within the band were moving north-northeast. One cell in northeast Davidson County began to show weak rotation. Considering the distance from the radar and velocity sampling problems so far from the radar, a Tornado Warning was issued for Davidson and Forsyth Counties, and then for Guilford County. The rotation strengthened as it moved into Guilford County, and a tornado was reported near Stokesdale. Additional thunderstorms were moving into the southern portions of the CWA on the southern end of the band. The radar/warning duties were divided between two forecasters one covering the northern portion of the CWA and the other the southern portion. Tornado warnings were issued for Moore and Chatham counties. Once the storms moved east of this area, the storms no longer showed a strong rotation signature. However the environmental winds were so strong just above the surface that even weak convective cells could produce wind damage. Another area of thunderstorms developed on the southern end of the rain band and evolved into a bow echo that eventually moved across western Harnett County and into Wake County. A MARC (mid-altitude radial convergence) signature was noted in the SRM velocity, and base velocity values with this bow were over 60 kts in the lowest radar slices. As the bow tracked north and moved into Wake County, the straight-line winds it produced became aligned orthogonal to the radar beam. Thus the radial velocity values diminished greatly. However the bow structure in the reflectivity pattern was still intact, so a Severe Thunderstorm Warning was issued for Wake County. This storm produced a 79 mph gust at the Raleigh-Durham International Airport (RDU). Yet another cluster of storms developed in the rain band and produced wind damage in Hoke County and western Johnston County.

Selected Photographs of the Severe Weather Event Photos courtesy of Guilford County Emergency Management, Stokesdale Fire Department, Doug Schneider, Darin Firgurskey and Jeff Orrock. (Click the image to enlarge.)

Case Study Team Phill Badgett Douglas Schneider Michael Strickler Michael Brennan Jeff Orrock Darin Figurskey Jonathan Blaes For questions regarding the web site, please contact Jonathan Blaes. NWS Disclaimer.