Storm Surge/Tide — Coastal Chatham, Georgia

2017-09-11 · Coastal Chatham, Georgia

Event narrative

Storm surge associated with Tropical Storm Irma had widespread significant impacts in Chatham County. According to Chatham County Emergency Management, 7 homes were destroyed, 369 sustained major damage, and 445 sustained minor damage. The Savannah River did breach onto River Street, but water remained out of businesses. Storm surge damage was most extensive on Tybee Island, specifically on Lewis Avenue and the southwestern portion of the island. Homes on Pelican Drive were also damaged by surge. Some storm surge related damage occurred to homes on Dutch Island and Burnside Island. Highway 80 between Savannah and Tybee Island was closed due to saltwater covering and inundating the roadway. Several rescues were performed as surge trapped people in their homes. USGS high water mark analysis revealed storm surge related inundation ranging from 1.19-5.25 feet above ground level across coastal portions of the county. The peak inundation value of 5.25 feet above ground level was taken from a high water mark at Oakridge Golf Course on Skidaway Island. Another notable high water mark of 3.28 feet above ground level was analyzed on 6th Street near Lewis Avenue on Tybee Island. A National Weather Service storm survey team found significant erosion on Tybee Island with most if not all of the dune line eroded away by storm surge and wave action. Furthermore, in some areas on the Tybee Island beach, approximately 6-10 feet of dune escarpment was found washed away. The National Ocean Service tide gauge at Fort Pulaski measured a peak tide level of 12.24 feet Mean Lower Low Water (MLLW) or 4.73 feet Mean Higher High Water (MHHW). This tide value ranks as the 2nd highest on record for the Fort Pulaski gauge and the peak surge value measured during the event was 5.63 feet. Extensive flooding took place at the Fort Pulaski National Monument area including the visitors center. A picture taken by National Park staff showed a water line indicative of 17 inches of water inside one of the park structures.

Wider weather episode

Irma first developed into a tropical storm on August 30th about 420 miles west of the Cabo Verde Islands, and within 24 hours strengthened into a hurricane. Irma continued to intensify and became a major hurricane over the eastern Atlantic on September 1st. After undergoing a brief period of weakening on September 2nd, Irma once again strengthened into a major hurricane on September 3rd and maintained major hurricane status through September 10th when it made landfall on the southwest Florida coast. During this extended period as a major hurricane, Irma set numerous intensity records for a hurricane in the Atlantic basin. Maximum sustained winds reached 185 mph, making Irma the strongest storm on record to exist in the Atlantic Ocean outside of the Caribbean and Gulf of Mexico. Also, Irma's 185 mph maximum sustained winds are tied for the second strongest maximum winds all time in an Atlantic hurricane. The minimum central pressure reached during Irma's life cycle was 914 mb which is the lowest pressure on record by an Atlantic hurricane outside of the western Caribbean and Gulf of Mexico. Furthermore, Irma maintained Category 5 status for 3 consecutive days which is the longest on record for an Atlantic hurricane. Irma stayed on a general westward track through September 5th when it began a gradual turn to the west-northwest. On this west-northwestward track, Irma eventually skirted along the north coast of Cuba on September 9th before turning northward toward Florida on September 10th. Irma officially made landfall at Marco Island, FL at 3:35 pm September 10 as a Category 3 hurricane. Following landfall, Irma tracked to the north-northwest and eventually the northwest as it progressed up the western side of the Florida peninsula. Irma steadily weakened during this time and was downgraded to a tropical storm near the big bend of Florida at 8:00 am on September 11th. Through the rest of September 11th, Irma tracked to the northwest into southern Georgia and widespread impacts occurred across the Southeast.

Despite the fact that the center of Irma tracked well to the west of the southeast Georgia and southeast South Carolina region, it still caused significant impacts due to heavy rainfall, strong winds, tornadoes, and storm surge. Feeder bands around Irma continuously moved onshore on September 11th and produced very heavy rainfall rates with rainfall totals generally ranging from 3 to 9 inches. The peak storm total rainfall of 9.07' was recorded by a CoCoRaHS observer near Beaufort, SC. Daily record rainfall totals for September 11th were recorded at all 3 climate sites in the area: 5.51' at the Charleston International Airport (KCHS), 4.53' at Downtown Charleston (KCXM), and 4.74' at the Savannah-Hilton Head International Airport (KSAV). This widespread heavy rain resulted in several reports of flash flooding with water entering homes and businesses. Wind damage produced numerous power outages across the region with some damage to structures and numerous downed trees. The strongest winds were confined to coastal locations, but frequent gusts into the 40-50 mph range occurred well inland. The maximum sustained wind recorded was 59 mph by the Weatherflow site on the Folly Beach Pier (XFOL) and the maximum wind gust recorded was 76 mph by the Weatherflow site near Beaufort (XBUF). One fatality and 1 injury occurred from trees falling on homes and across roadways in southeast South Carolina. The entire southeast Georgia and southeast South Carolina coast was impacted by storm surge generally ranging from 3 to 6 feet. This storm surge produced numerous reports of 4 to 6 feet of inundation above ground level, mainly along the southeast South Carolina coast. A peak surge of 4.87 feet occurred at the Charleston Harbor tide gauge at 2:00 pm while a peak surge of 5.63 feet occurred at the Fort Pulaski tide gauge at 5:42 am. Significant beach erosion occurred at area beaches with widespread damage to docks and piers all along the coast, as well as numerous reports of inundated roadways.

According to data received from the Georgia Emergency Management Agency, total damages from Irma in southeast Georgia were $29,150,000. This includes $20,000,000 in Chatham County, $2,900,000 in Liberty County, $2,900,000 in McIntosh County, $900,000 in Bryan County, $900,000 in Bulloch County, $300,000 in Effingham County, $250,000 in Candler County, $200,000 in Evans County, $200,000 in Jenkins County, $200,000 in Long County, $200,000 in Screven County, and $200,000 in Tattnall County. However, it should be noted that no explicit reports of damage from Irma were received from Effingham, Evans, or Screven counties. As such, no events were recorded in Storm Data for these counties. For all other counties, the total dollar damage amounts were divided equally across all Tropical Depression, Tropical Storm, and Storm Surge/Tide events.

Source: NOAA Storm Events Database, event_id 722665. Narrative written by the NWS forecast office that issued the report.