Tropical Storm — Coastal Nassau, Florida

2017-09-10 to 2017-09-11 · Coastal Nassau, Florida

Event narrative

This narrative is from the NWS Jacksonville Post Storm Report for Hurricane Irma which is a compiled list of reports from the storm survey, Emergency Management, private and public weather observation networks and broadcast media sources.

Tropical storm force winds with gusts to hurricane force, river flooding, storm surge and tornadoes impacted Nassau County from Hurricane Irma. On 9/11, a private weather station on Dunes Row at the south end of Amelia Island at a 60 ft elevation measured a wind gust of 106 mph, between 1 am and 2:30 am. At 3 am, several trees were blown down onto homes near Fernandina beach. At 2 am, the Fernandina Beach NOS tide gauge measured water level rises of 3.5 to 4 ft above MHHW datum.

The tidal gauge on the Atlantic coast at Fernandina Beach crested at 6.34 feet on Sept 11th at 0148 EDT. Moderate flooding occurred at this level. The St. Marys River at Interstate 95 crested at 3.57 feet on Sept. 11th at 1415 EDT. Minor flooding occurred at this level.

Storm total rainfall included 9.86 inches about half a mile north of Fernandina Beach, 9.93 inches 6.3 miles S of Fernandina Beach, and 12.70 inches in Fernandina Beach.

Wider weather episode

Hurricane Irma's eye passed west of the local forecast area, with the region on the storm's turbulent east side. Widespread tropical storm force winds with gusts to hurricane force were felt across much of the area, with the strongest winds surging up the Florida east coast during the pre-dawn hours of Sept. 11th. Extensive tree and power line damage occurred across the local area from the winds. One of the greatest local impacts exacerbated by Irma's rainfall and storm surge was river flooding. Prior to Irma's arrival, a local nor'eastern developed 3 days prior, with strong onshore flow pumping water into the St. Johns River basin. Elevated water levels of 1-2 ft above normal tidal departure were already ongoing for several tidal cycles before Irma's surge and rainfall. The nor'easter also brought localized heavy rainfall bands, with some areas near the coast realizing 4-6 inches in 24 hrs the days prior to Irma. In addition, precursor conditions to the nor'easter included an above average rainfall across the region during the summer months. Major, historic river flooding was forecast along Black Creek and the Sante Fe a week prior to Irma. Realized river values along the St. Johns surpassed prior record levels set by Hurricane Dora in 1964, during low tide the morning of Sept. 11th. The St. Johns River basin continued to rise with the combination of trapped tides due to the nor'easter, astronomically high tides heading into the spring tide season, storm surge of up to 5 ft in some areas, fresh water rainfall of 7-11 inches, and strong southerly winds pushing the water across the basin on the east side of Irma. Historic river flooding occurred across much of NE Florida Sept 11th through the following week as water levels were slow to funnel out of the St. Johns basin. Coastal infrastructure that was already weakened about 1 year ago due to Hurricane Matthew suffered the most damage from Irma's storm surge.

Source: NOAA Storm Events Database, event_id 720770. Narrative written by the NWS forecast office that issued the report.