FXUS64 KBRO 251117 AAA AFDBRO Area Forecast Discussion...UPDATED National Weather Service Brownsville TX 617 AM CDT Sat Sep 25 2021 .DISCUSSION...Updated for latest aviation discussion below. && .AVIATION...VFR conditions across Deep South Texas once again this morning. An easterly breeze picks up later this morning thanks to high pressure to our north. Some CU is expected this afternoon as a bit of moisture works back into the region. Overall, VFR conditions are expected the next 24 hours. && .PREV DISCUSSION... /issued 342 AM CDT Sat Sep 25 2021/ SHORT TERM (Now through Sunday): We are in the last gasp of the first appetizer of fall of the season. A mid-level ridge axis oriented over Central Texas today will get nudged east Sunday thanks to a closed low slowly ejecting out of northwestern Mexico and into the Desert Southwest. This pushes the surface high far enough east to allow a weak surface trough to lift into the western Gulf of Mexico. The best chance for rain through the short-term will be Sunday afternoon over our coastal waters thanks to the aforementioned trough and PWATs nearing 1.5". Highs today will be very close to seasonal normals, which is near 90 for most and lower to middle 90s in the Middle to Upper Rio Grande Valley. Meanwhile, lows tonight will still be a few degrees below normal with low to middle 60s expected for most away from the immediate coast. Highs Sunday are expected to be very similar to today with a touch more humidity thanks to increasing dew points. LONG TERM (Sunday Night through Friday): Not too many forecast changes were made in the long-term from yesterday afternoon's package. Mid-level subtropical ridging over the western Gulf/northeast Mexico will continue to weaken Sunday night and into Monday as a mid-level low positions itself over the Desert Southwest. Surface ridging will slide eastward along the southeastern US, allowing southeast winds to return across the region. This will increase both dewpoint temperatures as well as ambient temperatures through the early part of the upcoming week. Rain chances will also gradually increase, though probabilities will be highest along the coast and offshore through at least Monday. Better, and more wide-spread precipitation probabilities are expected starting Tuesday. A more robust and amplified mid/upper-level trough is forecast to progress eastward over the western CONUS on Tuesday, absorbing the remnant mid-level low over the Rockies as it does. As the trough continues to dig south and shift eastward, a profound upper-level jet streak will enter central/south-central Texas on Wednesday morning. The jet streak will cause upper-level divergence to occur over our area, helping increase rain chances through the remainder of the period. However, there is still lots of uncertainty and discrepancies in the mid-range deterministic models as mid-level ridging over Central America tries to retrograde northwestward and build over Southern Texas Wednesday afternoon. Depending on the trough's exact position/strength, the building ridge should push the jet streak northward, decreasing rain chances for deep south Texas. The ECMWF remains the outlier in the long-range deterministic models, keeping the jet streak right over Southern Texas, and thus the rain chances, through the second half of the period. For now, will continue to lean slightly more towards the drier GFS and GEM solutions but will keep a chance of scattered showers and thunderstorms Tuesday-Friday. Daytime temperatures will start off a few degrees above seasonal average Monday and Tuesday (mid-upper 90s and lower 100s west), perhaps even into Wednesday, but are expected to fall closer to or even a degree below average by Thursday (low-mid 90s). Meanwhile, lows will remain slightly above average through the period. MARINE (Now through Sunday): High pressure in the northwestern Gulf of Mexico will keep the pressure gradient weak and the seas calm through the weekend. As the high pushes east on Sunday, a surface trough will round the southwestern side of the high and help to bring a few showers and storms to our coastal waters as soon as Sunday afternoon. Sunday night through Friday: Mostly favorable marine conditions will persist Sunday night and on Monday as high pressure dominates over the Gulf. An area of low pressure will develop in the Plains Monday night into Tuesday. This will cause the pressure gradient to increase along the lower Texas coast, resulting in a slight increase of southeast winds and seas Tuesday through Wednesday night. Small Craft Advisories are not anticipated at this time, though SCEC conditions will be likely. Favorable conditions should return by Thursday. Showers and thunderstorms are expected to increase over the coastal waters by Sunday night as a weak surface trough combines with an upper level disturbance. Chances will persist through much of the upcoming week. && .PRELIMINARY POINT TEMPS/POPS... BAYVIEW/PORT ISABEL 85 70 88 74 / 0 0 10 20 BROWNSVILLE 90 70 91 74 / 0 0 0 10 HARLINGEN 91 67 92 71 / 0 0 0 10 MCALLEN 92 68 93 73 / 0 0 0 0 RIO GRANDE CITY 93 65 95 70 / 0 0 0 0 SOUTH PADRE ISLAND 83 78 84 80 / 0 0 10 20 && .BRO WATCHES/WARNINGS/ADVISORIES... TX...None. GM...None. && $$ This product is also available on the web at: https://weather.gov/rgv Short-Term/Aviation: 58-Reese/59-GB Long-Term/Upper-Air: 67-Mejia