Sunday, June 24, 2012

A Look Back at Hurricane #2 in 1940

The National Hurricane Center continues to forecast Debby to move west after a slow drift to the north. However, they have increased the intensity forecast as Debby passes south of the LA Coast. In fact, the latest forecast places Debby as a hurricane off the coast of Louisiana as it slowly moves westward on Wednesday and Thursday. However, as previously mentioned, much uncertainty still exists between various models, so the confidence of this forecast is marginal.

Source: The National Hurricane Center

Hurricane #2 from the 1940 season provides an interesting comparison if Debby does indeed strengthen into a hurricane off the LA Coast.This storm strengthened from a tropical storm to a hurricane south of Grand Isle, LA, then slowly tracked WNW before making landfall near the TX/ LA border.

Hurricane #2 from the 1940 hurricane season. Yellow = tropical storm, red = hurricane. Source: Unisys Corporation

The U.S. Army Corps document, History of Hurricane Occurrences along Coastal Louisiana, provides interesting insight into the 1940 surge event. Although the storm made landfall near the TX/ LA border, the highest observed storm tide value was observed far from the landfall area. The peak storm tide was 6.4 feet at Frenier, LA, on the southwest shore of Lake Pontchartrain!

Some storm tide observations, provided on page 29 of the document:

"It was accompanied by high tides and torrential rains in Louisiana. Port Arthur reported a wind velocity of 83 m.p.h. and a low barometric pressure of 28.87 inches. The hurricane produced tides of 4 feet at Port Eads; 6.4 feet at Frenier on the southwest shore of Lake Pontchartrain; 3.8 feet at Grand Isle; 4 to 5 feet near the mouth of Vermilion River; 5.6 feet at Schooner Bayou Control Structure, 16 miles south-southwest of Abbeville; 4.8 feet at Calcasieu Pass in the vicinity of Cameron; and 4.3 feet near Sabine."

Apparently, prolonged east winds piled up more than 6 feet of storm tide on the west end of Lake Pontchartrain in 1940. It is likely that water levels were also elevated near the Lake Borgne/ Shell Beach area, as well as along the levee of the Mississippi River, south of New Orleans. Storm tide values along the south Louisiana Coast generally ranged from 3.8 to 5.6 feet.

Now back to Debby. East and northeast winds along coastal Louisiana are already elevating water levels. Storm surge values at Shell Beach, LA were already approaching 2.5 feet this morning, according to NOAA Tides and Currents. I do not have a read on water levels at Frenier, although I may make a trip down there today or tomorrow to see for myself.

Once again, it should be stressed that the models remain uncertain and we should not just look at one possible scenario. All interests along the U.S. Gulf Coast, from Texas to Florida, should stay tuned to the National Hurricane Center, your local National Weather Service forecast office, and local media outlets for updates on this developing storm.

Check back often to this blog for the latest surge observations and historical comparisons. I will update the blog every morning and evening while Debby is in the Gulf of Mexico.

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