Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA
Issued by NWS New Orleans/Baton Rouge, LA
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686 FXUS64 KLIX 162100 AFDLIX Area Forecast Discussion National Weather Service New Orleans LA 400 PM CDT Sun Jun 16 2024 ...New SHORT TERM, LONG TERM, MARINE... .KEY MESSAGES... 1. The axis of heaviest rainfall has shifted further southwest, away from our forecast area. However, locally heavy rainfall could lead to some flash flooding concerns especially in urban and poor drainage areas on Monday and Tuesday. 2. Increasing onshore winds into the work week will bring a large enough fetch to cause coastal flooding concerns. Latest forecasts indicate coastal flooding of up to 1 to 3 feet above normally dry ground will be possible for east and south-facing shores by Tuesday and into the latter half of the week. 3. Hazardous marine conditions, especially for small crafts, are expected as winds and seas increase into the work week. Sustained winds are expected to be approaching 25 to 30 knots with gusts as high as gale-force (~34 knots) Tuesday and Wednesday. .SHORT TERM... (This evening through Monday night) Issued at 245 PM CDT Sun Jun 16 2024 Scattered showers and thunderstorms in association with a weak inverted surface trough continue to move inland over southeast LA this afternoon. Primary impacts are heavy downpours, lightning, and gusty winds in excess of 30-40 mph. This activity will gradually wane into the evening hours as daytime heating dissipates and weak subsidence from high pressure on the back side of the trough moves in. This will create a lull in rainfall tonight through early Monday morning. Monday we`ll see PWATs surge in excess of 2" (near daily record maximums) and more widespread convective coverage develop over the coastal waters and spread inland through the morning hours. Locally heavy downpours (rain rates as high as 2"/hour possible), frequent lightning, and gusty winds in excess of 35-40 mph will be the primary impacts, similar to today. With coverage being more widespread, however, this does increase the potential for localized flash flooding especially in urban and poor drainage areas. Be extra careful on your morning commute and give yourself extra time to arrive to work. Timing appears to focus heaviest rainfall through the first half of Monday with lesser coverage and concerns as we progress into the late afternoon and evening hours. Gradual deepening of a broad low over the Bay of Campeche up against a strengthening high pressure system over the southeast CONUS will generate a strong pressure gradient over the northern Gulf Coast. As such, surface winds will increase on Monday and continue to intensify through Tuesday. Immediate coastal areas where friction is weaker coming off the water will see sustained winds of 20-25 mph with gusts as high as 35 mph. This is right at the cusp of wind advisory criteria, but will hold off on this forecast package. If confidence increases in more frequent gusts exceeding 30 mph this would probably prompt issuance of one. While breezy, areas further inland will see reduced winds by comparison due to frictional forces as these stronger winds push inland. && .LONG TERM... (Tuesday through Saturday night) Issued at 245 PM CDT Sun Jun 16 2024 The plume of deep tropical moisture associated with the broad area of low pressure in the southwestern Gulf will continue to push westward in conjunction with the low moving toward the western Gulf coast. Based on the trends associated with the track of this low, the axis of heaviest storm total rainfall has shifted further southwest. Highest totals are still focused along coastal Southeast LA of 2 to 4" and lower amounts further inland and northeast. Tuesday should still see a fair amount of coverage of showers and storms with similar timing and impacts to Monday. Additional concern at this stage would just be the antecedent conditions present from any heavy rainfall that occurred on Monday. Rain chances will be tempered slightly Wednesday into the latter part of the week as drier continental air on the western flank of the surface high pressure is able to infiltrate from the northeast and decrease PWATs. This will put us back into a more typical summer convective regime with morning marine convection and afternoon thunderstorms. Slightly more ridging is able to nose into the latter part of the week which will help dry things up and help us see more sunshine (and heat things up slightly). Uncertainty is much higher Friday into the weekend as we monitor the progress of an inverted surface trough currently situated over the southwestern Atlantic. Some of the deterministic guidance has indicated the potential that this weak surface trough rounds the southern flank of the high pressure of the eastern CONUS and arrives into the area around this timeframe, but the exact track and strength of this feature varies greatly in the ensemble guidance. Just something to watch for now. && .AVIATION... (18Z TAFS) Issued at 1239 PM CDT Sun Jun 16 2024 Scattered SHRA/TSRA currently ongoing across HUM, MSY, NEW, ASD, and GPT along the coast with brief drops to MVFR/IFR CIGs/VIS and gusts as high as 30-35 mph, but should not be prolonged. Convection will continue to move inland and bring minor impacts to HDC, BTR, MCB in the next couple of hours. Loss of afternoon heating will begin to suppress storm coverage and there should be a lull with only isolated showers through overnight hours. Southeast winds will strengthen into the day with gusts upwards of 20 knots possible on Monday. Another round of storms is expected to form over the coastal waters and push inland at 12Z and beyond Monday morning. Widespread coverage of SH/TS will mean more prolonged impacts to terminals than seen today. && .MARINE... Issued at 245 PM CDT Sun Jun 16 2024 Have been dealing with clusters of storms producing gusty conditions across the waters, but should see a lull in activity overnight with weak surface high pressure nosing in. This also will briefly weaken the pressure gradient and result in winds relaxing, but this will be very short-lived. Conditions will gradually worsen Monday morning over the open Gulf waters as the pressure gradient between a high to the northeast and a low to the southwest strengthens. By tomorrow morning, small craft advisory conditions are expected to be in place as easterly winds ramp up to 20 to 25 knots. These easterly winds will remain in place through the end of the week and could further strengthen to near gale levels on Tuesday and Wednesday as the low to the southwest continues to deepen. Given the long fetch of these 20 to 30 knot winds from the southeast Gulf into the coastal waters a swell train of 3 to 4 feet is expected on top of the wind waves of 5 to 8 feet, and this will push seas to between 8 and 12 feet over the open Gulf waters on Tuesday and Wednesday. Additionally, water will continue to pile up on east and south facing shores over this period, and minor coastal flooding of 1 to 2 feet above ground level is expected from Tuesday through Thursday. A coastal flood warning may be necessary for areas around Lake Borgne and Bay St. Louis on Wednesday if confidence increases for inundation closer to 2.5 feet or so. Will monitor levels within Lake Pontchartrain as this fetch gradually funnels into the lake Thursday into Friday. The low in the southwest Gulf should move into Mexico on Thursday and Friday and the pressure gradient will begin to ease as the low weakens. Winds will slowly ease from 20 to 25 knots on Thursday to 15 to 20 knots by Friday. Given the extended duration of small craft conditions, a small craft advisory is in effect for the open Gulf waters and the Chandeleur and Breton Sounds from Monday morning to Thursday morning. There is the potential that winds could further increase into gale conditions, and a gale watch may be issued closer to the event on Tuesday and Wednesday. && .PRELIMINARY POINT TEMPS/POPS... MCB 72 85 71 83 / 30 90 20 50 BTR 76 87 76 86 / 40 90 30 70 ASD 76 88 76 87 / 50 80 50 70 MSY 79 87 79 86 / 60 90 60 90 GPT 77 87 76 86 / 60 80 50 60 PQL 75 90 75 91 / 60 80 40 50 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...Small Craft Advisory from 7 AM Monday to 7 AM CDT Thursday for LAZ068. Coastal Flood Advisory from 1 AM Tuesday to 4 PM CDT Wednesday for LAZ066>070-076-078. GM...Small Craft Advisory from 7 AM Monday to 7 AM CDT Thursday for GMZ536-538-550-552-555-557-570-572-575-577. MS...Coastal Flood Advisory from 1 AM Tuesday to 4 PM CDT Wednesday for MSZ086>088. GM...Small Craft Advisory from 7 AM Monday to 7 AM CDT Thursday for GMZ538-550-552-555-557-570-572-575-577. && $$ SHORT TERM...TJS LONG TERM....TJS AVIATION...TJS MARINE...TJS