933 FXUS64 KBRO 131651 AAB AFDBRO Area Forecast Discussion...UPDATED National Weather Service Brownsville TX 1151 AM CDT Tue Jun 13 2023 ...New UPDATE... .UPDATE... Issued at 1136 AM CDT Tue Jun 13 2023 Latest surface observations across Deep South Texas already show heat indices (HI) climbing above 100F for most locations late this morning. Comparing with observations from about this time yesterday morning, HI's are about a degree or two warmer on average. With that said, decided to issue out a Heat Advisory for all of Deep South Texas, with the exception of the Barrier Island, between 1 PM and 7 PM CDT again today. Models indicate some dry air mixing in across Zapata, northern Starr, and Jim Hogg Counties after noon, which may inhibit HI rising above 110F. Nevertheless, impacts will still be the same. It is extremely important to keep yourself cool and hydrated this week, especially if working outdoors for a prolonged period of time. Wear lightweight and loose fitting clothing when possible. 67-Mejia && .SHORT TERM... (Today through Wednesday) Issued at 254 AM CDT Tue Jun 13 2023 We'll start by looking back on Monday, not for the purpose of "Monday morning quarterbacking," but rather to enter into the official record what occurred and what did not occur. Forecast highs were as follows: BRO 94, PIL 93, HRL 97, MFE 98, TXW 97, EBG 98, APY 103, HBV 100, and BKS 102. Observed highs were as follows: BRO 95, PIL 94, HRL 95, MFE 98, TXW 99, EBG 98, APY 103, HBV 101, and BKS 102. The forecast highs were the result of starting with NBM guidance and adjusting downwards based upon the previous few days of observations, so when compared with actual observed high temperatures, forecaster intervention shows value. At 125 PM CDT Monday, a Heat Advisory was issued for all of Deep South Texas and the Rio Grande Valley except the island portions of Cameron, Willacy, and Kenedy counties. This followed a 325 AM CDT Monday Special Weather Statement where heat index values of 106 to 110 degrees were expected for the afternoon hours of Monday. The criteria for a Heat Advisory for WFO BRO is heat indices of greater than or equal to 111 degrees sustained for greater than or equal to two consecutive hours. Looking at observed heat indices for the above mentioned sites, the Heat Advisory appears to have verified for only Hidalgo County and Brooks County. Again, this is not an attempt to "Monday morning quarterback," but rather an attempt to figure out where we are in order to know where we're going. So, what does all of this mean for the short term forecast period (Tuesday and Wednesday)? CONSShort was once again the model of choice for dewpoint temperatures. Meanwhile, for high temperatures, NBM was the starting point, and adjusting downwards of several degrees was performed, especially over the central and western portions of the BRO CWFA, where (likely) unrealistic highs were progged by the NBM (APY 110-111, HBV 104-106, BKS 105-107, MFE 102- 104). The combination of the forecast ambient air temperatures and forecast atmospheric moisture yields heat index values generally in the range of 106 to 110 degrees for the afternoon hours of the period, with isolated pockets of heat indices of 111 to 112 degrees. Thus, will once again issue a Special Weather Statement for expected heat index values today. Finally, why has there been a disconnect between NBM's scorching high temperatures and actual observed values over the past several days? One reason could be the position of the 500 mb ridge, which is progged by model guidance to remain centered over northeast Mexico through at least the next 48 hours. Past exceptional heat events were the result of a mid-level high centered more over the Four Corners area of the United States. Another reason could be soil moisture. On March 28, the U.S. Drought Monitor indicated Extreme Drought within Zapata County, Jim Hogg County, Brooks County, most of Kenedy County, and the western portion of Starr County, with the remainder of the BRO CWFA (Hidalgo, Willacy, and Cameron counties) generally in Severe Drought. As of June 6, no drought exists anywhere within the BRO CWFA, the likely result of multiple mesoscale convective systems producing scattered to numerous showers and thunderstorms, many strong to severe. A portion of the solar insolation is possibly being diverted for the evaporation of this abundant soil moisture instead of being used 100 percent for heating the air column, which would occur if soils were parched, such as in a drought situation. How long the soil moisture will be a factor remains to be seen in the coming days, especially since the 141 PM CDT Monday Temperature and Precipitation Summary for Deep South Texas lists .38 inches of evaporation for Brownsville, .36 inches for Falcon Dam, .27 inches for McCook, .40 inches for Rio Grande City, and .15 inches for Weslaco. The bottom line? It's hot, and with the position of the above mentioned 500 mb ridge possibly shifting more north and west over time, the heat will be maintained, if not increased. Combined with steadily drying soils and no significant precipitation likely with the ridge hanging around, the likelihood of a widespread Heat Advisory, and possibly Excessive Heat Warning, will increase with time. && .LONG TERM... (Wednesday night through Monday) Issued at 254 AM CDT Tue Jun 13 2023 The 500mb ridge settles across Deep South Texas by the weekend and holds into next week, with surface high pressure across the Gulf. This bumps heights toward 595 dam and will allow temperatures to gain a few degrees, near record highs, through the remainder of the long term period. So far this week, highs have underachieved by a few degrees, but as the ridge builds stronger and the overnight heat continues, there should be little to stop the triple digit heat from taking over. Expect Heat Indices to top out near 110-115 and locally higher every afternoon, driving Heat Advisories through the period, although model guidance has not been handling dewpoints very well either. Have trimmed dewpoints a little lower. Fire weather may become more of an issue over the weekend or into early next week, with RH values along and west of US281 dropping below 30 percent and potentially into the teens across Zapata County, with 20 foot winds becoming breezy each afternoon. Still feel most areas will fall below any fire weather criteria, but current guidance now leans towards Fire Danger Statements potentially Saturday through Monday. && .AVIATION... (06Z TAFS) Issued at 1216 AM CDT Tue Jun 13 2023 MVFR to VFR will be the rule at the aerodromes through the next 24 hours. Moderate to breezy winds are also anticipated. && .AVIATION... (06Z TAFS) Issued at 1216 AM CDT Tue Jun 13 2023 MVFR to VFR will be the rule at the aerodromes through the next 24 hours. Moderate to breezy winds are also anticipated. && .MARINE... Issued at 254 AM CDT Tue Jun 13 2023 Now through Wednesday...Buoy 42020 reported south-southeast winds around 18 knots gusting to around 21 knots with seas slightly under 4.5 feet with a period of 5 seconds at 150 CDT/650 UTC. An enhanced pressure gradient over the western Gulf of Mexico will produce moderate to breezy winds and generally moderate seas along the Lower Texas Coast during the period. Small Craft Exercise Caution is likely, especially for the Laguna Madre and Gulf of Mexico waters from 0 to 20 nautical miles offshore, and a Small Craft Advisory cannot be ruled out for this area on Wednesday. Wednesday Night through Monday...Southeasterly winds will maintain Small Craft Caution conditions each afternoon into early evening across the bay and nearshore waters, shifting further offshore each night. Small Craft Advisories may be needed into Thursday and again Monday, but at this time, it does not seem to be a slam dunk SCA event. && .PRELIMINARY POINT TEMPS/POPS... BROWNSVILLE 96 80 95 80 / 0 0 0 0 HARLINGEN 98 77 97 78 / 0 0 0 0 MCALLEN 101 78 99 79 / 0 0 0 0 RIO GRANDE CITY 104 76 106 77 / 0 0 0 0 SOUTH PADRE ISLAND 87 81 87 82 / 0 0 0 0 BAYVIEW/PORT ISABEL 95 77 92 79 / 0 0 0 0 && .BRO WATCHES/WARNINGS/ADVISORIES... TX...Heat Advisory until 7 PM CDT this evening for TXZ248>255-351- 353>355. GM...None. && $$ SHORT TERM...66-Tomaselli LONG TERM....56-Hallman AVIATION...66-Tomaselli