Wednesday, June 21, 2017

Cindy Generates Widespread 2-4 Foot Storm Surge with Localized Maximum Exceeding 6 Feet

While Tropical Storm Cindy's torrential rains have grabbed the headlines, coastal flooding in Southeast Louisiana and Mississippi inundated some communities with saltwater.

Cindy generated widespread 2-4 foot storm surges in the region, with a localized maximum exceeding 6 feet at Shell Beach, Louisiana. The highest storm surge levels occurred east of the Mississippi River, even though the center of circulation has been moving to the northwest, with a likely landfall location near the Texas/ Louisiana border.

Peak storm surge levels observed through Wed Jun 21 at 900AM CDT. Data provided from NOAA Tides and Currents

Shell Beach, Louisiana, observed the highest storm surge so far, with a surge level exceeding 6 ft (1.83 m). At 1:06AM local time this morning, the tide gauge observed a water level 6.07 feet higher than predicted astronomical tides. Water levels had been consistently rising through the evening under sustained  northeast winds exceeding 35 mph and often gusting more than 45 mph.

The map above depicts peak storm surge levels through 900AM Central Time today. Bay Waveland Yacht Club at Waveland, Mississippi, and New Canal Station in New Orleans, both observed storm surge levels in the 3.5- 4.0 ft range.

Wind and water observations for Shell Beach provide insight into the localized nature of storm surge. Water levels peaked following a period of sustained winds from the northeast. This wind direction pushes water directly into Shell Beach, which may seem unusual as we may picture onshore winds along the northern Gulf Coast blowing from the south.

Graph depicting observed water levels (top), wind direction and wind speed (middle) and temperature (bottom) for Shell Beach, Louisiana, through the afternoon and evening of Tue Jun 20, 2017. Data provided by NOAA Tides and Currents, markups by Dr. Hal Needham.

However, Shell Beach is actually exposed to the northeast, so Cindy provided an ideal wind direction to pile up storm surge.  As Tropical Storm Ida passed to the east in November, 2009, Shell Beach observed peak water levels as winds blew from the north-northeast, even as this wind direction caused surge levels to fall in nearby coastal Mississippi. Shell Beach broke all kinds of rules during Ida- it even observed the highest storm surge record for the storm, although it was located to the LEFT of the storm track.

Tropical Storm Cindy also produced coastal flooding west of the Mississippi River, on LA-1 heading into Grand Isle. Chris Roberts uploaded the following photograph to a Facebook post yesterday evening, depicting coastal flooding over LA-1 before sunset.

Photo: Chris Roberts

As Tropical Storm Cindy tracks to the northwest, expect storm surge levels to build in Southwest Louisiana and the Upper Texas Coast. Storm surge levels in this region should reach 2-4 above normal astronomical tides, inundating coastal roads.

I will try to take the ferry to the Bolivar Peninsula this evening to observe any coastal flooding before sunset. This location, northeast of Galveston, has experienced substantial coastal erosion during previous decades, and observed the highest water level for Hurricane Ike.

The table below provides estimated peak storm surges for Tropical Storm Cindy through 900AM on Wed Jun 21. Data provided by NOAA Tides and Currents:

Shell Beach, LA:                             6.0 ft
Bay Waveland Yacht Club, MS:      4.0 ft
New Canal Station (New Orleans): 3.5 ft
Grand Isle, LA:                                2.6 ft
Pascagoula, MS:                              2.6 ft
Galveston, TX:                                2.4 ft
Sabine Pass, TX:                             2.3 ft
Pilot Station (near mouth of Miss): 2.3 ft
Calcasieu Pass, LA:                         2.2 ft


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