Barry Moving Ashore: Heavy Rain Still to Come

After briefly attaining hurricane status this morning, Barry has made landfall near Intracoastal City, LA, and has since weakened back to a tropical storm. Wind gusts to tropical storm force are being felt across south-central Louisiana with New Iberia recently reporting a wind gust to 61 mph. Lafayette has also hit tropical storm force, reporting 40 mph during the past couple of hours. Even as far inland as Baton Rouge has had a few tropical storm force wind gusts.

Lake Charles, LA radar at 3:34 p.m. CDT (image source: GR2Analyst).
Radar shows that the north and west sides of Barry are largely devoid of convection, but some fairly robust convection exists to the south and southeast of the center. It is hard to get a read on how strong the winds are in this convection as Doppler radar doesn't have a great view of it. As an aside, wind must have a component moving towards or away from the radar for the radar to measure it. In this case, the wind in the region of interest is moving perpendicular to the radar beam, thus, the radar is unable to sample it. The best we have are surface observations, which as mentioned in the previous paragraph, have shown some wind gusts to tropical storm force.

This deep convection is also where the heaviest rain rates can be expected. While there are no rain gauges out over the Gulf of Mexico, radar estimates indicate rain rates of 1-2 inches per hour in some of this heavier convection. Infrared satellite imagery also shows some very cold cloud tops associated with this convection, providing another piece of evidence that this is where we can expect some gusty winds and heavy rain. This convection should continue moving onshore as we go through the rest of the afternoon and into the evening.

GOES-16 infrared satellite channel showing very cold cloud tops associated with the convection just off the south-central Louisiana coast.
Taking a look at some of the high-resolution models, they continue to key in on very heavy rainfall tonight across parts of south-central Louisiana. Widespread rainfall totals over 10 inches, and localized pockets over 20 inches appear likely. The high-resolution models disagree on exactly where this bullseye will be, but anywhere from Baton Rouge to Crowley (west of Lafayette), and down to the coast appears to be fair game.
"Postage stamp" plot of the various high-resolution forecast models showing where they expect the heaviest rain.
High-Resolution Ensemble Forecast System (HREF) localized probability matched mean forecast precipitation from 7 p.m. CDT Saturday through 7 p.m. CDT Sunday.
Without getting too far into the weeds, probability matched mean basically takes the average of all the different high-resolution models, and creates a spatial distribution of the forecast rainfall. Afterwards, it shifts around the values based on the probability that a given point in the model will see certain rainfall rates. If that makes your head spin, don't worry about it. All you need to know is that this is a technique that allows us to get a good "average forecast" that takes into account multiple models. This "average forecast" shows very heavy rainfall from roughly New Iberia to Baton Rouge, with values approaching and even exceeding 20 inches. It is important not to focus on the exact location that the model shows this heavy rainfall, but know that there is strong agreement amongst the models that somewhere in south-central Louisiana is likely to see very heavy rainfall, in some cases, exceeding 20 inches, by the end of Sunday. Simulated "future radar" from these models suggests that the heavy rain would likely begin this evening after dark, and continue into Sunday morning.

This is all a long way of saying that Barry is far from done with Louisiana, and heaviest rains are yet to come. People in South Louisiana, especially in places such as Lafayette, New Iberia, Morgan City, and Baton Rouge will need to remain vigilant as we go into the night, and avoid travel, as nighttime flooding is particularly dangerous.


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