Marine Weather Net

Southwest Pass of the Mississippi River to Port Fourchon, LA 20 - 60 NM Marine Forecast


15 - 20


15 - 20


10 - 15



The Marine Weather Forecast In Detail:
GMZ572 Forecast Issued: 343 PM CDT Sat Oct 23 2021

Tonight...Southeast Winds 15 To 20 Knots. Seas 3 To 5 Feet With Occasional Seas To 6 Feet. Dominant Period 6 Seconds. Slight Chance Of Showers After Midnight.
Sunday...Southeast Winds 15 To 20 Knots. Seas 3 To 6 Feet. Dominant Period 6 Seconds. Chance Of Thunderstorms In The Morning. Showers Likely Through The Day. Thunderstorms Likely In The Afternoon.
Sunday Night...South Winds 10 To 15 Knots. Seas 3 To 5 Feet. Dominant Period 6 Seconds. Chance Of Showers And Thunderstorms.
Monday...Southwest Winds Near 10 Knots Becoming West In The Afternoon. Seas 2 To 4 Feet. Dominant Period 6 Seconds. Slight Chance Of Showers And Thunderstorms.
Monday Night...West Winds 5 To 10 Knots. Seas 2 To 4 Feet. Dominant Period 5 Seconds.
Tuesday...Northeast Winds Near 10 Knots Becoming East In The Afternoon. Seas 1 To 3 Feet. Dominant Period 5 Seconds.
Tuesday Night...Southeast Winds 15 To 20 Knots. Seas 1 To 3 Feet. Dominant Period 4 Seconds. Seas Building To 3 To 5 Feet After Midnight. Dominant Period 4 Seconds After Midnight. Chance Of Showers Through The Night. Chance Of Thunderstorms After Midnight.
Wednesday...South Winds 20 To 25 Knots. Seas 3 To 5 Feet With Occasional Seas To 6 Feet. Dominant Period 5 Seconds. Seas Building To 4 To 7 Feet With Occasional Seas To 9 Feet In The Afternoon. Dominant Period 5 Seconds In The Afternoon. Chance Of Showers And Thunderstorms In The Morning, Then Showers And Thunderstorms In The Afternoon.
Wednesday Night...West Winds 25 To 30 Knots Easing To 20 To 25 Knots After Midnight. Seas 6 To 10 Feet With Occasional Seas To 11 Feet. Dominant Period 7 Seconds. Showers And Thunderstorms Likely In The Evening, Then Chance Of Showers And Thunderstorms After Midnight.
Thursday...West Winds 20 To 25 Knots. Seas 5 To 8 Feet With Occasional Seas To 10 Feet. Dominant Period 7 Seconds. Chance Of Showers.
Thursday Night...Northwest Winds Near 25 Knots. Seas 8 To 12 Feet With Occasional Seas To 13 Feet. Dominant Period 7 Seconds. Chance Of Showers.
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Synopsis for Pascagoula to SW Pass Mississippi - GMZ501
Synopsis for SW Pass Mississippi River to Atchafalaya River- GMZ500
343 PM CDT Sat Oct 23 2021

A weak area of low pressure and cold front will pass through the waters on Sunday and Monday. High pressure will briefly settle in for Monday night and Tuesday, but a very strong low pressure system and front will impact the area Wednesday into Thursday.
Area Forecast Discussion
National Weather Service New Orleans LA
659pm CDT Sat Oct 23 2021

/issued 337pm CDT Sat Oct 23 2021/

Short Term - Tonight Through Monday night
A fast moving shortwave trough and a related jet streak will pass through the northern Gulf of Mexico during the day tomorrow. As this feature moves toward the region, an influx of deeper mid-level moisture will begin to feed into the coastal waters tonight and then into the southern portions of the CWA below I-10 by tomorrow morning. This deeper pool of moisture will allow for slightly steeper lapse rates and increased instability across the southern half of the CWA. This instability and the increase in forcing aloft will interact with a weak boundary lingering along the coast to produce scattered shower and thunderstorm activity mainly along and south of the I-10 corridor during the day tomorrow.

As the upper level vort max and jet streak moves further east tomorrow evening, the highest convective risk will shift toward eastern coastal waters and remain over these waters through the overnight hours. By Monday, this initial feature will no longer be impacting the region, but the trailing end of a northern stream trough axis and weak front pushing through the Midwestern states could spark off another round of isolated shower and thunderstorm activity during the afternoon hours. The best chance of convective development is expected over the eastern half of the CWA, generally east of I-55, where slightly more moisture and slightly stronger low level convergence along the weak front should be in place. Temperatures will be quite warm on Monday as increased compressional heating in advance of the front and trough axis occurs. Highs could climb into the lower 90s in many areas, and several record highs may be broken Monday afternoon. Any lingering convection will quickly dissipate in the evening hours due to a combination of increasing negative vorticity advection and decreasing instability.

LONG TERM (Tuesday through Friday)...A fairly deep and strong ridge axis will be in control of the forecast area on Tuesday with partly cloudy skies and dry conditions forecast throughout the day. Strong subsidence in the mid and upper levels will keep temperatures on the warmer side, and highs should climb into the upper 80s across much of the area.

This deep layer ridge axis will quickly shift to the east Tuesday night as a strong longwave trough deepens over the Southern Plains. Onshore flow will increase through the night, and a surge of deep tropical moisture will advect into the area. This is most evident when looking at forecast precipitable water values which are expected to climb from around 1.25 inches Tuesday afternoon to over 2 inches by Wednesday morning. Additionally, increasingly difluent flow in the upper levels will produce sufficient forcing to spark off some isolated to widely scattered shower and thunderstorm activity by late Tuesday night.

Wednesday will be the main day of concern as the longwave trough axis and an associated strong surface low and cold front sweep through the Gulf South. There are still some differences between the models concerning the exact timing and of when the trough will begin to eject out of the Southern Plains, but the models all indicate that the trough will take on a negative tilt as it moves through the region. As the trough becomes negatively tilted either Wednesday afternoon or Wednesday evening in response to a 100+ knot jet streak rounding the base of the trough, the cold front will race to the east and a line of strong to potentially severe thunderstorms can be expected as this front pushes through Wednesday afternoon into Wednesday evening. The severe potential will be highly dependent on several factors which will become better defined over the coming days. This includes the orientation and position of the low level jet, how Pacific based moisture influences lapse rates and instability values, and the exact timing of the frontal passage. The evolution of this severe threat will continue.nue to monitored over the next couple of days, and confidence on the primary convective mode will be narrowed down. In any event, the strong forcing and ample moisture in place, support categorical Probability of Precipitation for Wednesday into Wednesday night.

Model differences become more substantial on Thursday and Friday with the GFS indicating a dry and stable airmass dominating the forecast area, and the ECMWF (European Centre for Medium-Range Weather Forecasts) indicating a more unsettled period of weather. The reason for these differences if wholly dependent on how far south an upper level low digs into the Southeast. The GFS has the upper low transiting across the Tennessee Valley which keeps the forecast area embedded within a deep layer northwest flow regime. If this pattern verifies and dry and stable airmass with stronger cold air advection will take hold of the area. The ECMWF has a much deeper trough initially, and this results in the closed upper level low forming over north Texas and then pushing east along the I-20 corridor. This more southern solution results a colder 500mb airmass moving through the area which in turn will steepen mid-level lapse rates and encourage the development of clouds and showers through the end of the workweek. Given the substantial differences between the models, have opted to stick with the NBM which shows a risk of scattered showers each day and moderately cooler temperatures.

AVIATION...Prevailing VFR conditions will largely be the rule through tomorrow afternoon. At KMCB and KHUM, a brief window for some light MVFR (Marginal Visual Flight Rules) fog development may occur around daybreak, but this will be highly conditioned on the strength of the boundary layer flow and how much cooling can occur tonight.

A brief period of increased gradient flow over the Gulf waters will push winds into the 15 to 20 knot range tonight through tomorrow night. This increased wind field will be the result of a weak low pressure system passing through. After the low pulls east, a weak front will slip through the waters tomorrow. High pressure will build in behind the front, and offshore winds could increase to 10 to 15 knots from 5 to 10 knots for Tuesday. By Wednesday and Thursday, a much stronger low pressure system and cold front will impact the waters. Small craft advisory and potentially gale conditions could affect portions of the coastal during this period of time.

NOAA New Orleans LA Office: Watches - Warnings - Advisories
LA...None. GM...None. MS...None. GM...None.