Saturday, September 3, 2011

Lessons Learned from 1943

Track of the Unnamed 1943 Hurricane/ Tropical Storm

This morning The Weather Channel reported that surge has flooded some areas near Chef Menteur, LA to a depth of around one foot. Prolonged easterly or southeasterly winds tend to pile up water in that area east of New Orleans.

This may be a similar setup in some ways to the 1943 surge event in SE Louisiana. An unnamed hurricane spun off the Texas Coast on Sept 17 and 18, then headed northeast towards Louisiana as a tropical storm on Sept 19 and 20. This setup provided prolonged onshore winds in portions of SE Louisiana. Around three feet of surge was reported in the Chef Menteur area, even though the storm track was hundreds of miles away.

Quote from Times Picayune, Sept 20, 1943:

Storm winds of 40 to 50 miles per hour which had been predicted for New Orleans as the hurricane hovered in the Gulf did not materialize Sunday, but rain throughout the day caused some streets to be flooded, though not as extensively as Saturday. From 6 p. m. Saturday to 1:13 p. m. Sunday, the weather bureau recorded .69 inches of rain here.

Lester Corley, district manager of the highway department, reported late Sunday afternoon that approximately 36 inches of water covered the New Orleans approaches to Pontchartrain bridge on Highway 11 and the road was closed to all traffic except heavy busses. Water, he said, partially covered Highway 90 between Highway 11 and Chef Menteur.

Unnamed 1943 Storm and Hurricane Juan (1985) May Provide Perspective on Lee's Surge Potential

The Unnamed 1943 hurricane spun off the Texas Coast, making a loop before heading NE into Louisiana.

Hurricane Juan (1985) made multiple loops as it approached the SW Louisiana Coast.

An unnamed 1943 Hurricane and Hurricane Juan (1985) may provide insight into TS Lee's storm surge potential. Although both of the previous storms were hurricanes, they spun off the Northern Gulf Coast, and were downgraded into tropical storms while still impacting the region.

The unnamed 1943 storm revealed one of the most interesting surge histories in the SURGEDAT dataset. Research originally looked for peak surge levels along the Texas Coast, however, the highest surge located for this storm occurred east of New Orleans, on Highway 11 near Chef Menteur. Prolonged onshore winds put around 3 feet of surge over Highway 11 in that storm, which translates to a surge level of approximately 6 feet. What is truly amazing is that this peak surge level occurred hundreds of miles from the storm's track.

Hurricane Juan generated a more typical storm surge, as the peak surge level was closer to the storm's track. Juan generated a peak surge of 8 feet at Cocodrie, LA.

These previous storms provide insight into the surge potential of TS Lee. The unnamed 1943 storm provides a great example of surge overwash occurring at considerable distance from the storm's track, especially in SE Louisiana, where prolonged east or southeast winds can pile up enough water to flood roadways.