Historic rainy period continues

Published 7:00 am Saturday, July 17, 2021

By Skip Rigney

As of Friday morning, July 16, it has rained somewhere in Pearl River County every day for the past four weeks. On all but four of those 28 days, it has rained almost everywhere in Pearl River County. That’s according to data from the National Weather Service (NWS) radar in Slidell and several rain gauges scattered throughout the county.

This has been one of the rainiest stretches on record, not only in our county but in surrounding areas of southern Mississippi, southeast Louisiana, and southern Alabama. One Pearl River County rain gauge reported 15 consecutive days with rain.

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For comparison, here are the records for most consecutive days with measurable rainfall from nearby regional stations with historical data spanning periods from 30 to 125 years: Poplarville (13), Bogalusa (15), Slidell (11), Hattiesburg (14), Gulfport (13), Biloxi (14), New Orleans (16), and Mobile (17). Almost all of these record streaks occurred during the summer months of June, July, or August, although a few were tied by equivalent streaks in the winter.

This past Wednesday and Thursday were two of only three days during the past four weeks when the NWS radar indicated that rain fell on half or less of Pearl River County. The subtropical ridge of high pressure centered over the Atlantic Ocean, sometimes called the “Bermuda High,” temporarily extended further westward into our area and suppressed the number of showers that popped up Wednesday and Thursday.

However, the reduction in showers appears to have been only temporary. The Bermuda High has once again pulled back from the central Gulf States.

As during most of this summer, during the upcoming week, southern portions of Louisiana, Mississippi, Alabama, and the Florida Panhandle are forecast to be in an area of lower pressure between the Bermuda High to our east and another high pressure system over the western United States.

In the absence of the sinking air motion associated with high pressure systems, our warm, muggy air will continue to bubble upward each day, forming puffy clouds, some of which become rain clouds.

The weakness in the pressure field across the central Gulf of Mexico and northern Gulf Coast will become a more serious concern if it persists into August. Tropical disturbances in the Carribean Sea will tend to be drawn toward that weakness in the pressure field.

There are two additional disturbing signals as we head toward the peak of the hurricane season. First, one long-range computer model is predicting that high pressure will tend to be stronger-than-normal over southeastern Canada from August through October. That pattern typically blocks tropical storms and hurricanes from re-curving over the western Atlantic, and instead sends them further westward toward the southeastern United States.

The second caution flag is that there’s a better than even chance that the tropical Pacific Ocean will head back into the cool phase known as La Nina during the September-November period.

La Nina is usually associated with lower wind shear over the tropical Atlantic, and thus a more active hurricane season. La Nina was in place last fall and was one of the factors that resulted in 2020 being the busiest Atlantic hurricane season on record.