Storm Surge and Storm Tide Summary, Hurricane Dolly along SPI and Laguna Madre

Photo of very rough waters in Laguna Madre, Bayside, South Padre Island (click to enlarge)

Port Isabel Tide Chart, predicted and observed, during Dolly's passage (click to enlarge)

Minor Storm Surge Flooding Accompanies Dolly
Laguna-side Flooding More Impressive on South Padre Island on July 23, 2008

City/Town	County	Srg	Tide	Time	Remarks
Port of Brownsville	Cameron	4.00E	5.00E	930E	Estimated at the Ship Channel entrance
South Padre Island	Cameron	4.00E	4.00E	1230E	Bay water inundated west end of SPI. Esperanza street 4 feet of water and water flowing down Gulf Boulevard.
Port Mansfield	Willacy	3.03	5.12	1436	Measured by tidal gage
Port Mansfield	Willacy	3.00E	4.00E	1330E	Estimated by Harbormaster
Port Isabel	Cameron	2.95	3.87	800	Peak tide 8 AM CT; Peak Surge 912 AM CT
Rincon del San Jose	Kenedy	2.33	5.99	0418-0510/24	Peak surge several times between 0430 and 500 AM
South Padre Island	Cameron	2.00E	3.00E	945E	Mayor reported 3 feet of water breaching dunes before wind shift

E = Estimated

Dolly's rapid intensification just prior to landfall, combined with her slow crawl northward just east of South Padre Island, changed the result of Storm Surge flooding for residents along both sides of the lower Laguna Madre during the morning and afternoon of July 23^rd. While the initially expected surge values (generally 3 to 5 feet, above) largely materialized across the area, and contributed to minor to locally moderate inundation, the resultant bayside flooding proved once again that actual landfall location of a hurricane eye can make all the difference in how much, and where, storm surge flooding develops.

Cameron: Through 10 AM
Rapidly increasing northeasterly flow offshore quickly built seas in the Gulf to more than 18 feet soon after daybreak, along with an 11 second wave period. The rightward turning of the current into the shoreline quickly boosted tides above normal, at both the beachside of South Padre Island and Port Isabel. Northerly flow at the coast maintained a flow into the east and northeast facing shorelines, with surge building to 3 to 4 feet.

Cameron: After 10 AM
Immediately after the center of circulation drifted north of latitude of the City of South Padre Island, winds shifted to northwest, then west, between 10 AM and Noon. Shortly after the winds backed, the southwestern eyewall intensfied, as did the winds (below).

Three-dimensional radar depicting eyewall over South Padre Island, noon CT July 23 (click to enlarge)

0.5 degree base reflectivity in three dimensional space as Dolly's Eyewall pounded SPI.

During the most intense period of winds, which were dominant from the west and west southwest, bayside storm surge of up to 4 feet rapidly developed, inundating areas west of Laguna (Gulf) Boulevard, and adding to the ongoing urban type flooding as a result of the torrential rains. Gulf Boulevard was totally under water, and other eyewitnesses claimed that the bayside surge stretched across the resort town during the peak of the winds, a little after 1 PM. Erosion from the prolonged period of hurricane force westerly winds shows clearly in these before and after images (courtesy of NASA).

Baffin Bay Tide Chart, July 22 through 24 (click to enlarge)

Tides for Baffin Bay (just north of Kenedy County), showing initial tide drop, than a sharp rise after landfall

Port Mansfield to Kenedy County
Dolly's landfall on uninhabited South Padre Island along the Cameron and Willacy County line, with a resumption of a west northwest motion, allowed a more typical tidal surge to develop, particularly in Laguna Madre adjacent to the Padre Island National Seashore. Port Mansfield, which remained in the north and east eyewall, experienced an estimated 4 foot storm surge during the early afternoon as Dolly reached land. Farther north, at both Rincon del San Jose (southern Kenedy County) and Baffin Bay (above), the tidal rise was delayed into the evening and overnight hours of the 23^rd and 24^th, respectively, until southeast to southerly flow shoved high water levels northward. Measured surge at the Rincon del San Jose gage was 2.33 feet, with a storm tide of nearly 6 feet, during the wee hours of July 24^th.