155 FXUS64 KMOB 221159 AFDMOB Area Forecast Discussion National Weather Service Mobile AL 659 AM CDT Sun Aug 22 2021 .AVIATION... 12Z issuance...VFR conditions were observed across the area early this morning. These conditions are expected to persist through the period with the exception of temporary MVFR to IFR ceilings and/or visibilities in and around the heavier convection that may develop. Generally expecting scattered showers and thunderstorms to develop this afternoon, with the greatest coverage occurring along the coast. By mid to late evening, showers and storms should decrease to more isolated coverage. Winds will remain southwesterly to westerly. /14 && .PREV DISCUSSION... /issued 503 AM CDT Sun Aug 22 2021/ NEAR TERM UPDATE /Now Through Monday/...An upper level low resides over the Mid-Atlantic states and will slowly Fujiwara with Hurricane Henri along the northeastern coastline of the U.S. today. This interaction will pull Henri inland over the northeastern U.S. and pivot the trough axis (associated with the upper level low) to the east through Sunday evening. The upper level ridge over the ArkLaTex region seizes this moment to build in further east over the region gradually transitioning flow aloft from northerly to more northeasterly by Monday. Weak disturbances within the flow between the trough/ridge pair continue to percolate across the southeastern U.S., with a transient mid to upper level disturbance coming through Sunday afternoon and evening. A broad and very weak surface high meanders around the northern Gulf of Mexico through the period while a weak surface trough over central Alabama and Georgia slowly sags south on Monday. It sounds like a broken record, but we are once again expecting scattered showers and thunderstorms across the area today. With the trough axis shifting east and more ridging over our area, it stands to reason that the best coverage will be mainly over the eastern and southern portions of the CWA, with more isolated to scattered convection over northwestern portions. SBCAPE values upwards of 2,500j/kg with MLCAPE values towards 1,500j/kg will aid in thunderstorm development in the afternoon. Some slight drying in the mid levels may promote stronger downdraft production, reflected in higher DCAPE values of 750 to 1,000j/kg. Although 2+ inch PWATs are still maintained across southern portions of the CWA, these values do come down slightly in our northern counties, generally in the 1.9 to 2.1 inch range. This is still more than enough to foster heavy rainfall potential in thunderstorms, and minor nuisance flooding will be of concern where stronger storms develop on Sunday. Model guidance suggests convection may linger into the late evening hours Sunday, remaining isolated to scattered in coverage. Sundays highs will top out in the lower to middle 90's. Sunday night will see lows in the lower to middle 70's. Heat indices will range between 100 to 106. Convective activity looks to be slightly less on compared to what we've seen the last few days. Mid level dry air continues to filter in to the area, and PWATs start to come down a good bit in the 1.5 to 1.8 inch range. At the moment, opted to maintain scattered to likely PoPs, mainly across coastal counties where the seabreeze will act as a source of forcing. PWAT's in these coastal areas are still around 1.8-2 inches, but if models guidance starts to bring the drier air further south, these may have to be adjusted down in future updates. Any storm that does manage to get going will have strong wind gust potential, with DCAPE values generally 1,000 to 1,300j/kg. With less cloud cover and convective coverage, Monday will be a fairly hot day with mid 90's for highs, and some isolated spots reaching the upper 90's. Heat indices will range between 103 and 108. If confidence increases on heat indices reaching the upper end of this range over a larger area, a heat advisory may become necessary for Monday. A MODERATE risk of rip currents is in effect through Monday. Swell heights continue to trend downward to around 1 ft, although there appears to be a surge of long period swell around 10 seconds that approaches local beaches later this afternoon. For now, opted to keep MODERATE risk as this swell packet is not expected to linger for long. However, this is something we will continue to monitor throughout the day. 25/14 SHORT TERM /Monday night Through Tuesday night/...An expansive upper level ridge of high pressure will remain centered over the vicinity of the ArkLaTex Monday night into Tuesday and will slowly build east/northeast toward the Mid-Mississippi Valley region through Tuesday night. Our forecast area will remain positioned along the eastern and southeastern periphery of the upper level ridge through the short term period. Hot temperatures and rising heat indices will become an increasing concern early this week with the building ridge and this will be discussed a bit more in detail below. A weak surface trough of low pressure will meanwhile continue to extend from southern portions of southeast MS into interior southwest AL Monday night into Tuesday morning, but it does appear that this feature will gradually lift N/NW and become more diffuse Tuesday afternoon into Tuesday night. Isolated to scattered convection may develop near the immediate coast and adjacent offshore waters Monday evening/night and will keep low POPs in the 20-30% range near the immediate coast through the Monday night period. Precipitable water values will range between 1.7-2.0 inches across much of our forecast area by Tuesday afternoon across locations along and to the southeast of the surface trough axis. MLCAPE values also look to average between 1500-2500 J/KG across much of the region. The plentiful moisture and instability along with weak ascent provided by weak impulses in the northeasterly flow aloft and some low level convergence will aid in the development of scattered to locally numerous showers and thunderstorms across the region on Tuesday. The best convective coverage (50-60%) will be focused along southern portions of the CWA near the seabreeze, while slightly lower chances (20-40%) will be in place across interior southeast MS and southwest AL. A few storms will be capable of producing brief strong/gusty winds, frequent lightning, and locally heavy downpours. As mentioned above, heat concerns will increase early this week as the ridge aloft expands eastward. High temperatures on Tuesday are forecast to range between 93-98 degrees across most locations along and north of the I-10 corridor and slightly cooler between 90-93 along the immediate coast and beaches. High afternoon dewpoints between 70-75 inland and in the mid to upper 70s along the coast will likely result in maximum heat index readings between 105-110 over much of the region. A Heat Advisory may become necessary over a good portion of the forecast area Tuesday and we will need to monitor trends closely. Lows Monday night and Tuesday nights will continue to range in the lower to mid 70s inland and in the upper 70s to around 80 degrees along the immediate coast and adjacent beaches. /21 EXTENDED TERM /Wednesday Through Saturday/...A deep layer ridge is expected to be aligned from the Mid-Atlantic to Texas on Wednesday. The ridge is expected to weaken slightly late in the week as an inverted trough moves westward from the Atlantic into the southeastern states. The end result will be a continuation in the hot and muggy pattern with scattered to locally numerous showers and thunderstorms developing each afternoon. Rain chances may be slightly higher later in the period depending on how the aforementioned feature develops. High temperatures will begin in the lower to mid 90s but cool slightly to the lower 90s by late week. Hot and humid conditions will lead to heat indices in the 100-106 degree range through at least Thursday. Lows in the low 70s inland to mid and upper 70s along the coast will continue. /13 MARINE...Light to occasionally moderate southwesterly to westerly flow will continue through Monday, becoming southerly on Tuesday. Southeasterly flow will then take hold on Wednesday and will prevail through mid-week. Scattered to locally numerous showers and storms can be expected over the marine area each day. Frequent lightning in addition to higher seas and winds will be possible near any storms that develop. Seas will remain around 2 feet through Tuesday, building to 3 to 4 feet Wednesday and Thursday due to the southeasterly fetch. /14 && .MOB WATCHES/WARNINGS/ADVISORIES... AL...High Rip Current Risk until 6 PM CDT this evening for ALZ265-266. FL...High Rip Current Risk until 6 PM CDT this evening for FLZ202-204- 206. MS...None. GM...None. && $$ This product is also available on the web at: http://weather.gov/mob