Saturday, September 1, 2012

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 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 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: It appears that this pattern is widespread and most likely applies to some of the flooding caused by Hurricane Isaac in Louisiana.