Area Forecast Discussion
Issued by NWS Brownsville, TX
Issued by NWS Brownsville, TX
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941 FXUS64 KBRO 181655 AAB AFDBRO Area Forecast Discussion...UPDATED National Weather Service Brownsville TX 1155 AM CDT Wed Sep 18 2024 ...New AVIATION... .SHORT TERM... (Today through Thursday) Issued at 328 AM CDT Wed Sep 18 2024 Key messages: * Oppressive heat builds today and likely peaks Thursday, with heat index values ranging from between 105 to 112 away from the coast. * A Special Weather Statement for elevated heat indices is in effect this afternoon. Better chance for Heat Advisories is on Thursday. * Outside of local sea breeze driven showers or isolated storms, no significant widespread rainfall is expected through tomorrow. Midlevel high pressure over Texas will continue to slowly dry out the mid levels and minimize rain chances today and tomorrow. Any showers and thunderstorms that do develop will be isolated in nature and most likely develop along the sea breeze boundary. With that said, PWATs are still around 2 inches, which is equivalent to the 75- 90th percentile of SPC sounding climatology for the Brownsville, TX upper air site. Any showers or thunderstorms that do develop over the next couple of days will be capable of producing brief heavy rainfall that could lead to ponding or localized minor flooding along low lying and poor drainage areas, especially with the ground being saturated across portions of Hidalgo and Cameron counties from recent rainfall. Heat index values are expected to top out in the 108 to 112 range this afternoon. While some locations, especially along and west of the I-69C/US-281 corridor, could briefly approach Heat Advisory criteria (i.e. heat indices of 111+ for 2 or more hours), better confidence in Heat Advisory issuance will be on Thursday when the mid level ridge builds in stronger across our region. Therefore, we have opted to hoist a Special Weather Statement for elevated heat indices today roughly along and east of a Rio Grande City-Encino line. There is a low probability of an upgrade to Heat Advisory for parts of the area this afternoon depending on actual conditions but once again, confidence in more widespread 111+ heat index values is higher for Thursday afternoon. Our forecast thinking is in line with the WPC experimental heat risk tool, which indicates widespread moderate (level 2 of 4) heat risk across the RGV this afternoon but a mix of moderate and major (level 3 of 4) heat risk tomorrow afternoon. Overnight lows are only expected to cool into the mid 70s to low 80s tonight. As mentioned above, Thursday is likely to feature the most widespread oppressive heat across the RGV. Actual air temperatures will likely make a run for mid to upper 90s across portions of Hidalgo and inland Cameron county. With dew points in the mid to upper 70s, this will yield maximum heat indices in the 109 to 115 range, which would trigger the issuance of a Heat Advisory. There does remain some uncertainty in how high or prolonged the 111-115 heat index values get for Thursday, as some hi-res CAM guidance indicate the potential for isolated to widely scattered showers with embedded thunderstorms developing across the RGV. Additionally, drier air from top of the boundary layer may well mix down to the surface, keeping heat index values more manageable in the 105 to 110 range. Either way, please exercise precaution if spending extended amount of time outdoors today into tomorrow. && .LONG TERM... (Thursday night through Tuesday) Issued at 328 AM CDT Wed Sep 18 2024 The long term begins Thursday night with a mid-to-upper level ridge centered over central/western Texas, which will continue to result in near-normal to slightly above normal temperatures across Deep South Texas on Friday and Saturday. Additionally, with dewpoints reaching into the upper 70s, combined heat indices across most of the County Warning Area (CWA) are expected to range from around 105 F to 111 F on Friday with the highest indices across the mid and upper RGV though still nearing 110 across inland portions of Cameron, Willacy and Kenedy counties. A Special Weather Statement (SPS) will likely be needed on Friday for these areas. Saturday is expected to be a bit cooler as an upper level trough over California pushes eastward and begins to break down the ridge over Texas. As a result, the heat indices are expected to not range as high on Saturday though an SPS may still be needed across the mid and upper RGV as heat indices may reach up to 108 F. Models are in fair agreement that precipitable water (PWAT) values are forecast to be at least 1.5 inches to near 2.0 inches on Friday, which is near-to-above normal for this time of the year. Additionally, with the exception of Zapata and Jim Hogg counties, there is about a 20% to near 30% daily chance for afternoon showers and thunderstorms along the seabreeze boundary as it pushes westward with the best chances of rain along and east of the I-69 Corridor. Drier air may filter southward into the CWA and temporarily reduce POPs on Sunday. As the new week begins, the combination of lowering mid-level heights and the approach of an inverted trough over the Gulf of Mexico may increase cloud coverage and bring an uptick in convection along the afternoon seabreeze boundary, especially along and east of the I-69 Corridor, where POP`s could reach as high as 35% across the lower RGV. Temperature-wise, afternoon highs are expected to generally reach into the lower 90s across inland Deep South Texas with mid 80s across the barrier islands. Overnight lows are anticipated to fall into the mid to upper 70s away from the coast Friday and Saturday morning and then ranging from the low to mid 70s through the rest of the period. Meanwhile, along the lower Texas coastline, lows will remain in the upper 70s to lower 80s. && .AVIATION... (18Z TAFS) Issued at 1148 AM CDT Wed Sep 18 2024 VFR conditions now with few to sct low clouds and light southeast winds. Weak sea breeze convection is activating near KBRO, and may see a few to sct showers popping up over the next few hours. VFR should continue but brief MVFR near convection may occur. VFR tonight as well. && .MARINE... Issued at 328 AM CDT Wed Sep 18 2024 Now through Thursday...Generally favorable marine conditions will prevail with light winds and seas around 1 to 2 feet. Chances of isolated showers and thunderstorms will continue at times through the forecast period that could lead to locally enhanced winds and seas. Thursday night through Tuesday...Light to moderate winds and light seas are expected Thursday night through Tuesday with seas generally ranging 1 to 2 feet through Saturday becoming 2 to 3 feet through Tuesday. There is a slight chance of showers and thunderstorms daily, which may result in heavy rainfall and elevated winds. && .PRELIMINARY POINT TEMPS/POPS... BROWNSVILLE 92 79 93 78 / 20 0 30 10 HARLINGEN 93 76 94 75 / 20 0 30 0 MCALLEN 97 79 98 79 / 10 0 20 0 RIO GRANDE CITY 95 78 96 77 / 10 10 20 10 SOUTH PADRE ISLAND 88 82 88 81 / 10 10 20 10 BAYVIEW/PORT ISABEL 90 78 91 77 / 10 0 20 10 && .BRO WATCHES/WARNINGS/ADVISORIES... TX...None. GM...None. && $$ SHORT TERM...54-BHM LONG TERM....68-McGinnis AVIATION...54-BHM