Lake Borgne Marine Forecast
|Rest Of Today...Northeast Winds 5 To 10 Knots. Waves 1 To 2 Feet. Dominant Period 4 Seconds. Chance Of Showers And Thunderstorms.|
|Tonight...Northeast Winds 5 To 10 Knots. Waves 1 To 2 Feet. Dominant Period 4 Seconds.|
|Thursday...Northeast Winds 5 To 10 Knots Becoming Southeast Late In The Afternoon. Waves 1 To 2 Feet. Dominant Period 4 Seconds. Slight Chance Of Showers And Thunderstorms In The Afternoon.|
|Thursday Night...South Winds 5 To 10 Knots Becoming Southwest After Midnight. Waves 1 Foot Or Less. Dominant Period 4 Seconds.|
|Friday...Northeast Winds 5 To 10 Knots Becoming South In The Late Morning And Afternoon. Waves 1 Foot Or Less. Dominant Period 4 Seconds. Chance Of Showers And Thunderstorms.|
|Friday Night...Southwest Winds 5 To 10 Knots. Waves 1 Foot Or Less. Dominant Period 4 Seconds. Slight Chance Of Showers And Thunderstorms.|
|Saturday...West Winds Near 5 Knots Becoming South In The Afternoon. Waves 1 Foot Or Less. Dominant Period 4 Seconds. Chance Of Showers And Thunderstorms In The Morning, Then Showers And Thunderstorms Likely In The Afternoon.|
|Saturday Night...Southwest Winds 5 To 10 Knots. Waves 1 Foot Or Less. Dominant Period 4 Seconds. Slight Chance Of Showers And Thunderstorms After Midnight.|
|Sunday...Southwest Winds Near 5 Knots Becoming South In The Afternoon. Waves 1 Foot Or Less. Dominant Period 4 Seconds. Chance Of Showers And Thunderstorms In The Morning, Then Showers And Thunderstorms Likely In The Afternoon.|
|Sunday Night...Southwest Winds 5 To 10 Knots. Waves 1 Foot Or Less. Dominant Period 4 Seconds. Slight Chance Of Showers And Thunderstorms After Midnight.|
| Synopsis for Pascagoula to SW Pass Mississippi - GMZ501|
Synopsis for SW Pass Mississippi River to Atchafalaya River- GMZ500
935 AM CDT Wed Aug 4 2021
A stationary front will remain settled along and near coastal areas today, eventually sagging south into marine areas through late week. High pressure builds into the region this upcoming weekend and into early next week.
| Area Forecast Discussion|
National Weather Service New Orleans LA
1206pm CDT Wednesday August 4 2021
SHORT TERM (Today through Friday Night)... Early this morning, what is left of a weak stationary front remains draped across our CWA, or roughly from around Morgan City to Yscloskey. It's not a well defined front, with a broad thermal and surface pressure gradient but there is some reflection in curvature in surface winds owing to some degree of low-level vorticity and local convergence. More reflection is noted ascending into the 925 to 850mb layer and is nearly stacked aloft, with a sharp wind direction change from the east north of the front, to around from the west south of the front. The broad nature of the frontal zone has led to a region of relaxed low- level winds, as indicated by nearly calm surface to low-level flow. This proved to be a dynamic feature that led to scattered areas of minor flooding yesterday, with very little mean low-level storm motion within the of the frontal zone causing nearly stationary convection. Not to mention, broad troughing anchored across the eastern US which has placed the northern Gulf on the southern periphery of subgeostropic cyclonic flow leading to upwind propagation vectors oriented from the WNW. Knowing this, and identifying easterly 850mb transport vectors north of the front nearly opposite in direction led to back building convection, especially those along boundaries parallel to the mean low-level flow. Re-analyzing the past will help confidently identify features to monitor for today, but there will be some notable differences. Starting with early this morning on radar, spotty showers continue along remnant westward propagating outflow boundary just north of the frontal zone across coastal MS and tidal lakes. May need to monitor any nearby remnant boundary interactions especially near and across Lake Pontchartrain through daybreak. Hard to say if any development will ignite similar to yesterday as slightly drier air has settled into the region, but will keep a mention of isolated showers or storms a bit more towards the north than what NBM Probability of Precipitation suggested to be on the safe side to around the northshore and coastal MS. Meanwhile, ongoing nocturnal clusters of convection within much deeper tropospheric moisture and available instability will continue to ride east just south of the front within the warmer shelf waters. Can't rule out an uptick in storm strength later this morning to a few hours after daybreak leading to some strong to possibly severe marine storms, with wind gusts >34 knots and waterspouts the main risks. What is different going into today is a bit of a sharper tropospheric moisture profile has squeezed south pressing up against the front. Yesterday, drier air was noted to have pushed in at H5 and aloft but such deep low-level moisture kept average total column PW's elevated (which also was a factor that led to a few areas of flash flooding). With drier air winning over north of the front, continued descent in the mid-levels will strengthen and sink this inversion due to compressional warming, pulling down to nearly H7. Otherwise, drier air has trickled in the low- levels as well, which all combined factors has dropped PW's into the 1.5 to 1.75" range north of the front, to 2"+ along and south of the front. This will in turn lead to less convection expected today, which HREF members support across the board. The question will be moreso for later this morning, if any northeastward surging outflow boundaries can pull north enough underneath weak steering flow up around the I-10/12 corridor east of I-55. NBM PoP's came in with a fine gradient along the coast, but smoothed the transition and nudged isolated Probability of Precipitation just a notch north of the interstate in this region to account for any potential NE surge in bands of convection. Otherwise, subsidence really wins over going into the afternoon with not much left behind this initial E to NE moving cluster across coastal SE LA. Still, as mentioned yesterday if any convection can get going under enough daytime destabilization around the frontal zone, can't rule out an isolated strong storm that may have the potential to tap into some of the lower tropospheric dry air to produce gusty surface winds (DCAPE forecast in the 1100J/kg range). However, such "warm" tropospheric temperatures will really cause updrafts to struggle in this area and especially north of the front and am not anticipating any severe weather issues today. Also, due to the same weak steering flow in the frontal zone and back building environment north of the front, should any isolated convection attempt to get going later this afternoon, may need to watch for some isolated flash flooding but the threat should be limited. Something that will continue to be monitored.
The drier air really wins over later tonight pushing south into the northern Gulf, which fortunately will lead to less overall nocturnal convection across warmer shelf waters. It is worthy to note that the weak dynamic energy associated with the deeper convection ongoing this morning along and south of coastal SE LA attempts to create a weak cold pool(a region of relatively cold air) and associated meso-low, spinning up along the front drifting east of our outer Gulf waters. This should not be a concern for us fortunately even if this weak disturbance attempts at acquiring subtle tropical characteristics. But could in fact be an aid in drawing drier tropospheric air south into our area on the back side of this potential weak developing low. It will feel noticeably drier and a tad cooler for many come daybreak Thursday, with projected lows reaching the upper 60's as far south as around BTR east across the Northshore and parts of coastal MS, with some traditionally cooler locations getting close to the mid 60's. Not bad! Model soundings illustrate plenty of tropospheric drying and surface radiational cooling to support just barely lower forecast lows Thursday morning in these locations compared to deterministic NBM guidance, but did not get too far off the main road. But compared to the recent weeks (months?) of exhausting humidity, this will be a nice improvement.
During the day on Thursday, we mix out strongly by lateam into the afternoon hours with very little cloud cover other than some upper-level cirrus and typical (yet slightly elevated) spotty Cumulus clouds field. Even with projected highs reaching the low 90's, forecast max heat indicies will only range roughly 4-8 degrees warmer thanks to slightly lower dew points (higher across SE LA and near marine areas). Still cant rule out some isolated convection across land areas during peak daytime heating, with just enough instability above the LCL and beneath the strong subsidence inversion to support some shallow showers, but vertical growth will be hard to come by with very warm tropospheric temperatures above this inversion.
Very little changes going into Friday, other than a steady moistening trend in the low-levels leading to surface dewpoints returning back into the low to mid 70's. This will help support just a notch higher overall Probability of Precipitation coverage during peak afternoon heating, but still not seeing significant impacts aside from a rather typical summertime pattern closing out the week. Kind of nice for a change! KLG
LONG TERM (Saturday through Tuesday)... Shortwave trough near to east of the forecast area early Saturday will move northeast allowing high pressure at both the surface and aloft to build into the central Gulf Coast region from the east over the weekend. This deep layer ridging will then persist across the area early next week. Precipitable water values will likely fluctuate from 1.5 to 2.1 inches during this period. This should lead to a more typical but moist summer pattern we've had much of this summer with daytime and particularly afternoon Probability of Precipitation in the 50 to 60% (NBM) across all land areas according to the NBM and this forecast. The operational runs of the GFS and ECMWF (European Centre for Medium-Range Weather Forecasts) do not support the rain chances being this high every day during this period, but am leaning on the NBM since it has been verifying better with it's generally higher rain chances much of this summer. Temperatures are expected to be fairly close the seasonal averages for August. 22/TD
A nearby weak stationary front across inland portions of SE LA will persist in place today, with waves of showers and storms expected south of this front early this morning. A few storms may be locally strong or severe, with wind gusts greater than 34 knots and isolated waterspouts the main risks. Drier air attempts to filter into the region Thursday through late-week as the same front pushes south and eventually dissipates, reducing overall typical early morning shower and storm coverage. Otherwise, winds will remain light with waves/seas ranging 1-2ft for tidal lakes/sounds and 2 to perhaps 3ft for outer Gulf marine areas. KLG
NOAA New Orleans LA Office: Watches - Warnings - Advisories
LA...None. GM...None. MS...None. GM...None.