Much welcomed rain to continue across the Lower Rio Grande Valley and Deep South Texas into September 2

Rain, Cooler Temperatures Finally Arrive!
Relieving conditions to continue through midweek
Preliminary Rainfall since August 28th, as of 5 pm, August 31st
Location County Rainfall
Rancho Viejo
Cameron
3.01
Harlingen 4.7 WSW
Cameron
2.99
Hebbronville
Jim Hogg
2.63
Harlingen 4.3 WSW
Cameron
2.47
Santa Ana/Lower Rio Grande Valley
Hidalgo
2.42
Bayview/Cameron County Airport
Cameron
2.14
Harlingen/Cooperative
Cameron
1.43
Harlingen/Valley Airport
Cameron
1.44
Los Fresnos
Cameron
1.13
Falfurrias
Brooks
0.90*
Falcon Lake
Starr
0.86
Armstrong
Kenedy
0.75
Brownsville 4.5 NNW
Cameron
0.63
Brownsville SPI International Airport
Cameron
0.57

Overview
Those liquid drops from the sky are no lie. Indeed, like manna from heaven, some quenching and drenching rains have finally developed across Deep South Texas and the Lower Rio Grande Valley to end a record setting hot and dry summer (June through August) and ease the region into September. After thunderstorms soaked portions of the RGV with 1/2 to 3 inches of rain during the afternoon and evening of the 30th, additional showers and isolated thunderstorms should drop another 1/2 to 1 1/2 inches on average, with locally higher amounts should any deep thunderstorm systems develop through September 2nd. The rain, accomapanied by abundant cloudiness, has not only crushed the triple–digit heat wave, but should hold daytime temperatures in the 80s to aruond 90, some 3 to 10 degrees below average for the Valley until the 2nd.

Sunshine and warmer temperatures will return to close the week, and perhaps continue into the Labor Day weekend. However, with more moisture in the soil, lengthening nights and shorter days, and an atmosphere that is not as hot from top to bottom as was the case through summer, daytime temperatures should only rebound to their early September averages, which are generally in the lower to mid 90s except mid to upper 90s across the Rio Grande Plains. As of this writing, there is still some uncertainty for the holiday weekend, as the plume of deep moisture will be lurking not too far south of the border.

Pattern Matters
Subtle changes to the general summer pattern have made a large difference in the weather on the ground. The most significant difference is the development of a subtropical jet, located underneath an upper ridge that continues across the Four Corners region of the U.S. A weak longwave upper level trough, or disturbance, settled in near the Baja peninsula over the weekend of August 29th and 30th, with energy from the disturbance propagating eastward, across northern Mexico and eventually Deep South Texas. This energy combined with a weak low level trough to add tropical moisture from the lower levels to the higher level moisture supplied by the subtropical jet, seeding the atmosphere and setting the stage for increased rain potential. Smaller disturbances ejecting east from the larger system will continue to promote times of showers and thunderstorms through September 2nd. Current data suggest that the strengthening four corners ridge will bring enough north to northwest flow into South Texas to effective "shove" the deeper moisture southward into north central Mexico, bringing the aforementioned drier air back to Deep South Texas and the Rio Grande Valley.

Infrared satellite photo from August 31st, 1645 UTC (1145 AM CDT), showing persistent subtropical jet and deep moisture across Deep South Texas
Infrared satellite image showing deep moisture flowing along the subtropical jet (dark blue arrow). Some moisture from eastern Pacific Hurricane Jimena was feeding into the system.
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