Area Forecast Discussion
Issued by NWS Brownsville, TX
Issued by NWS Brownsville, TX
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803 FXUS64 KBRO 132317 AAA AFDBRO Area Forecast Discussion...UPDATED National Weather Service Brownsville TX 617 PM CDT Thu Jun 13 2024 ...New AVIATION... .SHORT TERM... (Tonight through Friday night) Issued at 151 PM CDT Thu Jun 13 2024 500mb high pressure axis along the New Mexico/West Texas border pivots eastward through Friday taking on an east to west orientation. Modest 1000-700mb layer moisture (55-75%) today lowers slightly Friday (55-65%) as subsidence from the passing center of the ridge squashes the limited available moisture below 700mb. The overall moisture content in form of precipitable water is shown to lower from 1.90 inches observed on the Thursday 12Z Brownsville sounding to a GFS forecast of 1.6 inches Friday. Satellite loops show a nice cumulus band along the sea breeze pushing inland with isolated showers noted over northern Kenedy, over Cameron County and south of the Rio Grande over Tamaulipas, Mexico as of 130 PM LT. Until sunset or shortly after, there remains a slight chance of showers or a thunderstorm west of I-69E as the sea breeze front traverses westward across the RGV/Deep South Texas. Thereafter, mostly clear and calm with mild to warm overnight temperatures of 75-80 degrees. Friday mostly sunny with a very low chance (10%) of a sea breeze shower with highs climbing well into the 90s to lower 100s. Local beaches will see highs reach the upper 80s. Another sultry night to start the weekend with lows only dipping into the 75-80 degree range. && .LONG TERM... (Saturday through next Thursday) Issued at 151 PM CDT Thu Jun 13 2024 Key message - We are watching the Bay of Campeche/Southwest Gulf for potential tropical development. While chances have increased for tropical development to the south (Southwest Gulf) over the next few days, any potential system is likely (at this writing) to ultimately move into Mexico, due in part to broad mid-level ridging holding sway over Texas and dissuading the northward movement of lower latitude systems. For reference, the NHC gives the chance for cyclone development as 40% for late this weekend or early next week. Regardless of the final outcome to the south, tropical moisture will be able to surge north, and local rain chances are forecast to trend upward, especially for Tuesday through Thursday. Saturday through Monday will feature afternoon sea breeze activity, with rain chances spreading a bit farther inland each day. On Saturday, a 700 mb inverted trough/tropical wave shows up in the models over the Southwest Gulf, deepening to 500 mb by Sunday. This trough will remain in place into the early part of next week. As mid-level ridging drops anchor and builds over the Southeast United States/Mid-Atlantic region, it will open up a path for tropical moisture to move north along the Northeast Mexican coastline toward the lower Texas coast. By Wednesday and Thursday, global models support the chance to likely categories of rain percentages. In terms of amounts, NBM deterministic numbers suggest that over an inch of rain can be expected for the lower Valley on both Thursday and Friday. More aggressive numbers, reflecting copious moisture and high rain producing efficiency, could start us out at an inch as early as Saturday, ramping up to around three inches for the 24 hours from Wednesday to Thursday. For the week, those worst case scenario numbers could support up to ten inches of rain for the lower Valley spread across the work week, but focused mainly from Tuesday through Friday. The Ranchlands and Mid-Valley worst case scenario rain accumulation amounts are on par with the lower Valley since potential rain bands will affect the entire CWA. Something to watch for in later forecasts, however, will be that if a potential system strengthens, it could actually start to impact rain chances downward, as some tropical moisture would be pulled closer to the storm, causing the heavier rainbands to remain farther south. However, since this tropical cyclone has yet to develop, the current thought process is to go with a more widespread (generous) rainfall scenario. The generally welcome rainfall will not be the only thing to impact the CWA over the course of the long term forecast. Because of an enhanced pressure gradient, stronger east to southeast flow will develop, generating larger swells that may lead to a higher rip current risk along the beaches, and even beach runup and coastal flooding concerns next week. As for temperatures in the long term, highs will start off in the range of upper 90s for most of Deep South Texas and the Rio Grande Valley, with a few areas in the triple digits, but will taper off by Wednesday to being mostly in the 90s, thanks to extra cloud cover and increased rain chances. Heat index values will continue in the 105 to 110 degree range through Tuesday, but will be lower, 102 to 107 degrees Wednesday and 95 to 105 degrees on Thursday, mid week. Low temperatures will be mostly in the 70s, but a few places could bottom out near 80. && .AVIATION... (00Z TAFS) Issued at 615 PM CDT Thu Jun 13 2024 VFR conditions are expected to generally prevail through the TAF period with persistent easterly winds and a briefly breezy sea breeze again Friday afternoon. An isolated shower or thunderstorm is possible along the sea breeze Friday, with coverage and confidence too low to add to this TAF package. && .MARINE... Issued at 151 PM CDT Thu Jun 13 2024 Tonight through Friday night...Models continue to show a weak pressure gradient persisting over the western Gulf of Mexico tonight, Friday and Friday night. Gentle to light south winds today back southeast to east Friday as upper level high pressure shifts eastward. Seas remain nearly flat with buoy 42019 reporting seas at 1 foot as of 1 PM today. Isolated showers and/or thunderstorm being observed offshore have a low probability reaching the Laguna Madre this today over this evening. Low probability continues for Friday for all coastal waters. Saturday through Tuesday night...Moderate east to southeast winds and moderate seas will slowly transition higher into the weekend. The weekend will feature moderate to fresh east to southeast winds and building seas. Gulf wave heights will approach small craft advisory criteria late in the weekend for the offshore waters, and may also reach small craft advisory criteria for the nearshore waters by early next week. Marine weather will remain unsettled, with isolated to scattered showers and thunderstorms possible through the long term. && .PRELIMINARY POINT TEMPS/POPS... BROWNSVILLE 78 97 80 96 / 10 20 10 40 HARLINGEN 74 99 75 97 / 0 20 10 40 MCALLEN 78 100 78 98 / 0 10 0 20 RIO GRANDE CITY 78 100 77 98 / 10 10 0 10 SOUTH PADRE ISLAND 82 89 83 88 / 0 20 20 50 BAYVIEW/PORT ISABEL 78 93 79 93 / 10 20 10 40 && .BRO WATCHES/WARNINGS/ADVISORIES... TX...None. GM...None. && $$ SHORT TERM...59 LONG TERM....54 AVIATION...56-Hallman