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Barry's Up to 20" of Rain in New Orleans and Southeast Louisiana Didn't Happen. Here's Why.
Published: July 15, 2019
As Hurricane Barry neared landfall on the Louisiana coast, dire rainfall forecast totals for New Orleans and parts of southeast Louisiana were calling for 10 to 20 inches of rain there, triggering fears of life-threatening flooding.
Those extreme rainfall totals did not pan out, despite pockets of heavy rain in southeast Louisiana.
Just over an inch of rain had fallen at Louis Armstrong International Airport in New Orleans from Friday morning through early Monday morning. New Orleans Naval Air Station only picked up slightly more rain with 2.40 inches reported.
So what happened?
Ahead of the storm, forecast model guidance painted a large gradient of rainfall totals over southern Louisiana, highlighting the uncertainty of where the heaviest rainfall would set up.
Exactly where the axis of huge rainfall totals set up would make a major difference in the flooding potential, but that focused area of heavy rainfall never developed over southeast Louisiana, including New Orleans, over the weekend.
Wind shear and dry air - two of the nemeses tropical cyclones sometimes face - likely played role in both limiting and delaying Barry's rainfall.
Strong northerly winds constantly pinned Barry's heaviest downpours offshore rather than over southern Louisiana during the weekend. Those winds pushed dry air into the northern half of Barry and kept the atmosphere to the north of its center less moist and less unstable.
"Typically, a tropical storm will have a lot of moisture, rainfall and wind on its entire eastern half," Ben Schott, meteorologist in charge of the National Weather Service office in Slidell told NOLA.com. "But as the drier air kept pushing into Barry, it limited its thunderstorm growth to the southern side of the storm, which is pretty unusual."
Computer model forecast guidance did not properly handle the dry air and wind shear Barry encountered, and therefore, forecast too much rainfall to the east of where the storm moved inland.
While Barry's rainfall wasn't extreme in southeast Louisiana, it has been in other parts of the state.
Doppler radar estimated rainfall totals of 10 to 15 inches in a narrow corridor from southwest to central Louisiana from late Sunday night into early Monday. Significant flash flooding was ongoing Monday morning in this area.
The band of heavy rain in southwest and central Louisiana developed on the southern side of Barry's circulation center which was located in Arkansas. It illustrates that major impacts from weakening tropical cyclones can continue well after landfall.
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