Hurricane Isaac Preliminary Maximum Storm Surge Levels

I've comprised a list of preliminary Hurricane Isaac maximum storm surge levels, taken from NOAA Tides and Currents (National Ocean Service), USGS tide gauges, and at least one anecdotal source. This list will probably grow as more data become available. Later this fall or this winter, the list will become official, as verified surge data and published reports become available.

Rank		Level_ft		Station Name	State	Agency/ Source	Datum
1		13.6		Lake Borgne Surge Barrier	LA	nola.com	NAT
2		11.02		Shell Beach	LA	NOS	NAT
3		10.9		Little Irish Bayou at I-10	LA	USGS	NAVD88
4		8		Bayou Laloutre at Ycloskey	LA	USGS	NAVD88
4		8		Bay Waveland Yacht Club	MS	NOS	NAT
6		7		Pass Manchac	LA	USGS	NAVD88
7		6.2		New Canal Station	LA	NOS	NAT
8		6.1		Liberty Bayou at Hwy 433	LA	USGS	NAVD88
9		4.6		Coast Guard Sector Mobile	AL	NOS	NAT
10		4.4		Pascagoula NOAA Lab	MS	NOS	NAT
11		4.3		Chickasaw Creek	AL	NOS	NAT
12		4.2		Grand Isle	LA	NOS	NAT
13		4		Mobile Bay at Hwy 193	AL	USGS	NAVD88
13		4		Pilots Station East, SW Pass	LA	NOS	NAT
15		3.55		Dauphin Island	AL	NOS	NAT
16		3.5		Pensacola	FL	NOS	NAT
17		2.5		Panama City	FL	NOS	NAT
18		2.2		Lawma, Amerada Pass	LA	NOS	NAT

 

Note: NOAA Tide and Currents (NOS) data are storm surge levels, or height above normal astronomical tide. USGS data are storm tide levels, measured above NAVD88 level. All data are preliminary.

How do these data fit into the larger context of storm surge history along the U.S. Gulf Coast? Are any of these surge levels unprecedented for a category-1 hurricane? How do these water levels compare to other surges in a specific location?

Although it's impossible to answer all of these questions on the surge blog, if you have specific questions like these, please contact "Hurricane" Hal Needham at hneedh1@lsu.edu. Hal maintains SURGEDAT, the world's most comprehensive storm surge database. SURGEDAT has currently archived more than 6,000 coastal high water marks produced by hurricanes and tropical storms along the U.S. Gulf Coast and U.S. Atlantic Coast. SURGEDAT also contains data for more than 250 peak surge events that have occurred internationally since 1880.
 

Lake Pontchartrain remains elevated, likely enhanced rainfall flooding

Lake Pontchartrain remains elevated today, more than three days since Hurricane Isaac made landfall in southeast Louisiana. Although the lake level has slowly been falling since early Thursday, the level was still about three feet above normal earlier this morning, according to the NOAA Tides and Currents gauge at New Canal Station on Lake Pontchartain. The water level at this location was at least four feet above normal for approximately 60 hours, beginning at around 10PM on Aug 28th until around 10AM on Aug 31st.

According to preliminary levels provided by NOAA Tides and Currents, the maximum level at New Canal Station was around 6.2 feet above normal. A USGS site at Pass Manchac, between Lake Pontchartrain and Lake Maurepas, reported a preliminary level of around 7 feet.

The prolonged storm surge event in Lake Pontchartain may have contributed to enhanced flooding from heavy rainfall around the lake. Flooding occurred in several communities near the lake, including Laplace, Mandeville and Slidell. It's likely that heavy rainfall could not drain as quickly as normal due to the storm surge inundation at the lake.

A similar situation happened in June near Tampa, Florida, when heavy rainfall runoff from Tropical Storm Debby was impeded by elevated water levels in Tampa Bay due to storm surge. Also, respondents to the Gulf Coast Climate Information Needs Assessment survey in the Houston/ Galveston area noted that heavy rainfall runs off slower when the level of Galveston Bay is elevated. (link: http://www.southernclimate.org/publications/Gulf_Coast_Assessment_Final.pdf). It appears that this pattern is widespread and most likely applies to some of the flooding caused by Hurricane Isaac in Louisiana.