FXUS64 KHGX 212308 AFDHGX Area Forecast Discussion National Weather Service Houston/Galveston TX 608 PM CDT Thu May 21 2026 ...New MESOSCALE UPDATE, AVIATION... .KEY MESSAGES... - A Flood Watch remains in effect for counties along the coast through Monday morning. - Multiple rounds of thunderstorms are expected through the holiday weekend and into next week. Some may be strong at times. Locally heavy rainfall is possible leading to the potential of flash flooding. - Mariners should be prepared for the multiple rounds of storms. Winds and seas will be higher in and near storms. && .MESOSCALE UPDATE... Issued at 607 PM CDT Thu May 21 2026 Shortwave from earlier today has mostly exited the region off to the east. Attention is turning to the shortwave and associated shra/tstms tracking SEwd toward the I-35 corridor in the Hill Country. This activity looks like it might pivot into parts of the Brazos Valley this evening where there is still some lingering instability that can be tapped into complements of some breaks of late afternoon sunshine. The overall instability should be declining as the hours wear on from debris clouds and sunset, but have nudged POPs up a touch across NW parts of the CWA for the next 6 hours or so and will continue to monitor trends. 47 && .DISCUSSION... Issued at 143 PM CDT Thu May 21 2026 As we did yesterday, I'll be keeping this discussion mainly focused on what's expected and the potential impacts as a result of that. If I use any fancy sciency words, I'll break em down and explain what it means and why its relevant. We are going into a holiday weekend, but that doesn't mean that it's time to completely disconnect from the weather forecast. The heavy rainfall threat Saturday into Sunday is of particular concern for the area. Continue to stay weather aware by keeping up with the latest forecasts and have multiple ways to receive alerts (especially if you outdoor plans or have plans to be on the road for the holiday weekend). This morning's (Thursday morning) round of convection remained mostly offshore, but did drop 0.5-2" of rainfall along the coast. This time yesterday, we were anticipating some of the heavier rainfall to occur along the coast...and for what it's worth we did see some radar estimated 3-6" amounts...in the Gulf waters. Now why am I admitting this? Because it goes to show just how difficult it is in this environment to be precise on the exact timing and placement of the heaviest convection. PW values remain near or above the 75th percentile (~1.60") this afternoon [moisture availability remains elevated] and there is some lingering shortwave energy [a source of lift], so some isolated to scattered showers/storms will be possible this afternoon. This is most likely to occur north of I-10 closer to a lingering frontal boundary. Fortunately, this spotty round of rain will be falling in areas that are not as vulnerable as the coastal areas. Keep in mind that soils along the coast remain fairly saturated after receiving 4-6+" of rainfall for areas along the coast (mainly Matagorda and Brazoria Counties). As a result, a Flood Watch remains in effect along the coast through Monday morning. There is decent potential that we'll expand the watch further northward and eastward by Friday morning based on rainfall/model trends. If you'd like to see more in-depth details on the Flood Watch, see the Hydrology section below. Speaking of rainfall, let's talk about when the next rounds of rain (after this afternoon) is expected. Some of the latest high resolution model guidance depicts a line of gradually decaying storms pushing into the area from the west later this evening. The models that reflect this have another round early Friday morning mainly along the coast/offshore. We saw this morning that model guidance did not capture the correct placement of convection. So, could this convection occur further inland, yes! Could it occur even further offshore, also yes! Either way, the threat for heavy rainfall along the coast persists which explains the current extent of the Flood Watch. There is some generally decent consensus on a dry-ish period going into Friday night, then comes our main timeframe of concern over the weekend. An upper level low that is currently situated off of the coast of California is gradually pushing its way eastward towards Texas. It looks to arrive generally in the Saturday to Sunday window. This will pair with PW values peaking near or above 2" (90th percentile: ~1.80") and the potential for frontogenetic banding. Think of frontogenetic banding as an area of locally enhanced convection...so heavier rainfall. In a moisture-rich environment such as this, rainfall rates could easily exceed 4" per hour in these types of bands and this potential extends into at least Sunday morning. There remains uncertainty on exactly where this will set up, but the potential is certainly there...so there will likely be an expansion of the Flood Watch area going into the weekend. The upper level low does look to move out of the area towards the end of the weekend, but PW values do remain elevated well into next week as another upper level trough approaches. So, rainfall potential will essentially continue for the foreseeable future. Keep in mind that each round of rain will help to saturate the soils for future rounds of rain. Saturated soils leads to quicker runoff, which leads to a quicker transition to flash flooding. As a result, there is daily potential for excessive rainfall for most or all of Southeast Texas through Monday/Memorial Day. The excessive rainfall risk alternates between a marginal risk (level 1 of 4) and a slight risk (level 2 of 4) each day through Monday, but this is subject to change once we gain confidence on timing/location of the heavy rainfall potential. Cannot entirely rule out an upgrade in the excessive rainfall risk on Saturday. As far as rainfall totals go, we're still anticipating additional amounts of 4-6" with isolated higher amounts through Monday...just keep in mind the confidence of the higher amounts remains low at this time. The bulk of the rainfall is anticipated to occur within the Saturday to Sunday timeframe. Be sure to stay up to date on the forecast for the latest details. In case you were curious about the temperature forecast, it's going to be highly dependent on the timing of these rounds of rain. For now, we have high temperatures mainly in the low to mid 80s through next week, but there may be times where the high temperatures remain in the 70s depending on the timing of rainfall. We may see high temperatures reach into the upper 80s next week depending on the next round of rain. Low temperatures will mostly be in the upper 60s to low 70s. Batiste && .AVIATION... (00Z TAF Issuance) Issued at 607 PM CDT Thu May 21 2026 A few lingering late day cells leftover from the shotwave that passed through earlier today should be waning early this evening for most of the area. However, we're watching another shortwave and associated storms in the Hill Country that could pivot into the CLL/UTS area this evening. Overall intensity trend should be declining with time...but we'll keep an eye on things. Otherwise, mainly VFR and dry for the rest of the region during the overnight period. With light winds, wet ground, and thinner cloud cover I wouldn't be suprised to see some patchy late night fog development across parts of the area. Next fairly weak shortwave and remnant light precip coming out of Mexico should make it into our southern terminal (IAH southward) in the 14-18z timeframe Fri. Unsure on overall coverage so have some PROB30s in the TAFs for now. Rest of Friday appears primarilly uneventful outside of some iso-sct tstm pop-ups associated with afternoon heating. 47 && .MARINE... Issued at 143 PM CDT Thu May 21 2026 Multiple rounds of showers and thunderstorms are anticipated through the holiday weekend, so mariners should take note for the potential for intermittent periods of elevated winds and seas in and around any of the stronger thunderstorms that push through the waters. The next round of showers and thunderstorms is expected either late this evening or Friday morning. Timing of storms beyond that is a bit uncertain, but additional rounds are expected into at least Monday. Outside of the storms, expect light to occasionally moderate onshore flow with 3-5 ft seas. Batiste && .HYDROLOGY... Issued at 143 PM CDT Thu May 21 2026 Multiple rounds of moderate to heavy rainfall are expected through at least Monday. Areas along the coast, especially Matagorda and Brazoria Counties, received 5-8" over the past 48ish hours. The next round of rain is expected to move in either late this evening or Friday morning. Some of this rainfall may occur along the coast, which brings the potential for flash flooding. As a result, a Flood Watch continues for coastal counties through Monday morning. The Flood Watch will likely be extended northward and eastward within the next 24 hours to cover the threat area for the Saturday into Sunday timeframe of concern. With PW values near or above the 90th percentile (~1.79") through the weekend, rainfall rates are expected to peak in the 3-4+" per hour range in the heaviest downpours. Anywhere we see these intense rainfall rates, localized flash flooding is possible. That being said, we are not anticipating widespread river flooding just yet; however, this will help prime the soils as we continue with a wet pattern. As we go into the weekend, multiple rounds of moderate to heavy rainfall on top of primed soils will generate runoff and cause rises on area rivers and watersheds. The greatest threat for heavy rainfall, flash and riverine flooding comes over the holiday weekend as intense rainfall rates will bring accumulated values of 4-6+" across most of Southeast Texas through Monday. Widespread action to minor stage flooding is expected with moderate to isolated major stage flooding possible depending on where the most rainfall accumulates. Remember that you can monitor updated river forecasts via the NWS NWPS webpage (https://water.noaa.gov/). Batiste/Landry-Guyton && .PRELIMINARY POINT TEMPS/POPS... College Station (CLL) 69 85 71 83 / 60 40 10 90 Houston (IAH) 70 86 73 84 / 30 40 10 90 Galveston (GLS) 75 85 78 85 / 30 40 10 70 && .HGX WATCHES/WARNINGS/ADVISORIES... TX...Flood Watch through Monday morning for TXZ226-227-235>238- 335>338-436>438. GM...None. && $$ DISCUSSION...Batiste AVIATION...47 MARINE...Batiste