Chandeleur Sound Marine Forecast
|Rest Of Today...Northeast Winds 10 To 15 Knots. Waves 1 To 2 Feet. Dominant Period 4 Seconds. Chance Of Showers.|
|Tonight...East Winds 10 To 15 Knots. Waves 1 To 2 Feet. Dominant Period 4 Seconds. Slight Chance Of Showers Early In The Evening. Chance Of Showers After Midnight.|
|Sunday...Southeast Winds 15 To 20 Knots Becoming Southwest Near 20 Knots In The Afternoon. Waves 3 To 5 Feet. Dominant Period 4 Seconds. Showers And Chance Of Thunderstorms.|
|Sunday Night...Northwest Winds 20 To 25 Knots. Waves 3 To 6 Feet. Dominant Period 4 Seconds. Slight Chance Of Showers In The Evening.|
|Monday...Northwest Winds 20 To 25 Knots. Waves 3 To 6 Feet. Dominant Period 4 Seconds.|
|Monday Night...North Winds 20 To 25 Knots. Waves 3 To 5 Feet With Occasional Waves To 6 Feet. Dominant Period 4 Seconds.|
|Tuesday...North Winds 15 To 20 Knots Easing To 5 To 10 Knots Late In The Afternoon. Waves 2 To 4 Feet. Dominant Period 4 Seconds.|
|Tuesday Night...East Winds 5 To 10 Knots. Waves 1 To 2 Feet. Dominant Period 4 Seconds.|
|Wednesday...East Winds 10 To 15 Knots. Waves 2 To 4 Feet. Dominant Period 4 Seconds.|
|Wednesday Night...Southeast Winds 10 To 15 Knots. Waves 2 To 4 Feet. Dominant Period 4 Seconds. Chance Of Showers After Midnight.|
| Synopsis for Pascagoula to SW Pass Mississippi - GMZ501|
Synopsis for SW Pass Mississippi River to Atchafalaya River- GMZ500
1005 AM CST Sat Nov 28 2020
A stationary front will remain over the offshore north central Gulf coastal waters today. A low pressure area is expected to develop along the upper Texas and southwest Louisiana coast tonight and then move east to northeast across the central Gulf coast region Sunday. The stationary front will lift back north as a warm front towards the coast tonight and Sunday morning, then a strong cold front will move through the region Sunday afternoon. Cold high pressure will build in its wake early next week. The high pressure area will move across the central Gulf coast region Tuesday and east of the region on Wednesday as another cold front moves into the western Gulf coast region.
| Area Forecast Discussion|
National Weather Service New Orleans LA
1148am CST Sat Nov 28 2020
Updated for 18z TAF issuance.
UPDATE... Cold front has pushed well out into the offshore Gulf coastal waters leaving a cooler and somewhat drier airmass over the forecast area. Best area of isentropic lift supportive of measurable stratiform rain has really shifted south to the coastal waters south and west of Terrebonne Parish. This lift along with higher rain chances should eventually shift back north and east this afternoon and especially tonight as the stationary front moves back north as a warm front. Modified the forecast somewhat today to suppress/delay the mentionable light rain and higher PoPs today, otherwise the remainder of the forecast appeared on track at this time.
AVIATION... Updated the TAFs to try to pinpoint the changing/borderline IFR/MVFR (Marginal Visual Flight Rules) and MVFR/VFR areas. Variability is likely to continue the next few hours, then more consistent MVFR (Marginal Visual Flight Rules) to IFR should develop as the rain starts to develop back north this afternoon and evening. Will hopefully have higher confidence with the 18z forecast issuance.
AVIATION...12Z TAF package...All terminals with the exception of HUM have dropped to IFR or LIFR status due to low cigs. Low cigs will be an issue all day and night for pretty much the entire area as they remain around 600 to 2k. Most of the terminals should be fine from a vsby standpoint and present weather through the day however HUM will likely have VCSH most of the day. SHRA (rain showers) should spread east through the night but TSRA will likely hold off until after 9z for the most western terminals. Winds will remain out of the northeast today and this evening and then begin to veer around to the east after midnight. /CAB/
SHORT TERM...The cold front has pushed all the way back into the Gulf while a band of light showers continues to lag back behind it. This band appears to be more associated with the h925 front and a mid level jet. This activity will continue to drift south and slowly dissipate as the jet streak slides east.
Today may be mostly quiet as we wait to feel the influence of the approaching mid level low. The disturbance at 9z was back in New Mexico and will slowly work into the southern Plains by this evening. This will lead to some weak ridging across the Lower Mississippi Valley and with that lift across the region will slack off some initially. This should cause most of the rain to dissipate until this afternoon, but there will probably still be a few showers across mainly coastal LA this morning. Weak isentropic lift will start set up just off to the west and that will increase across the area late this afternoon and through the night. This will lead to scattered showers developing over southwestern portions of the CWA this afternoon. As lift increases across the region overnight showers should become more widespread especially over the western half of the CWA. Thunder may still be quite limited overnight as we will still be lacking instability until just before sunrise.
Heading into Sunday there are a lot of question marks. Most importantly appears to be the track of the surface low. It will begin to develop along the northeast TX coast overnight Saturday and then should lift to the east-northeast and then eventually northeast Sunday and Sunday night. Where and how fast it does could be highly dependent on where convection develops. As always if there is a lot of convection north of the warm front, it could get anchored closer to the coast. This would favor a more southern track and thus keep much of the area out of the warm sector which in turn would limit the severe risk. The risk of moderate to heavy rain would still be in play as we should still have some elevated instability thus leading to thunderstorms and brief periods of heavy rain. Another concern is convection firing over the Gulf and along the coast. This would cut off LL moisture flow to the north and also lead to a slightly more southern track of the surface low. This scenario is beginning to be advertised by the some models but a majority of the guidance still suggest the surface low being able to come more inland and getting at least a good chunk of the CWA in the warm sector. This will keep the risk of severe weather possible across the region and Storm Prediction Center has the entire region in a Marginal Risk for severe storms. If the surface low is able to come well inland the risk for severe weather would increase. Biggest negative is instability. That still appears to be limited but if there are any breaks in the cloud cover there could be some modest destabilization of the atmosphere and given the amount of moisture and shear in place it would be more than adequate to get surface based storms to develop and if it can become deep enough would have the potential of being severe. 0-1 and 0-3km SRH could range from 200-400m2/s2(maybe higher) and 0-6km bulk shear of 45- 65kts suggest the potential is there for damaging winds and even a few tornadoes. A lot will hinge on the track of the surface low.
Convection and rain will quickly come to an end Sunday night as the strongest cold front of the season makes its way through the area. As our disturbance swings through the Lower MS Valley and into the TN Valley the surface low will begin to quickly eject northeast towards WV driving the cold front across the deep south and completely through the CWA. We will probably deal with clouds through much of the morning until the LL thermal trough slides by but even if the sun comes out, with h925 temps of 0-2C highs will struggle to get much above the lower to mid 50s, some locations across southwest MS may struggle to get into the 50s. This will set the stage for a chilly night and what a way to start the meteorological winter. Cold Air Advection is expected to remain strong through the night and even though winds are not anticipated to completely shut down, in fact LL winds will remain strong through the night, the strength of the Cold Air Advection will lead to our first freeze across a good chunk of the area. /CAB/
LONG TERM (Tuesday and beyond)... Tuesday morning will be the coldest morning in a long time across most of the area. Freezes possible, if not likely, north and west of Lake Pontchartrain. High pressure moves from the Texas coast Tuesday morning to off the Atlantic Coast by Thursday night. At that point, models begin to diverge. 18z and 00z GFS solutions emphasize northern stream shortwave at the end of next week, while the 12z ECMWF (European Centre for Medium-Range Weather Forecasts) emphasizes southern stream shortwave. While both models return moisture to the area Wednesday night and Thursday, with an attendant chance of precipitation, the GFS solution would start it about 12 hours earlier. In addition, the ECMWF solution would develop a significant surface low over the Gulf in our coastal waters as the northern and southern streams phase, strengthening the surface low it as it heads toward the Florida Panhandle Friday. The GFS is basically an inverted trough with surface pressures at least 10 mb higher.
Will take the middle ground on timing with no mention of precipitation until Wednesday night, mainly after midnight. Would note that if 12z ECMWF scenario becomes the preferred solution, Probability of Precipitation and winds from Wednesday night onward would need to be bumped up significantly from current levels.
Only real disagreement on temperatures through Friday will be for Thursday and Thursday night, which can be attributed to the vastly different surface patterns. Current forecast is in between the 2 solutions, so we can go either way depending on favored solution in later packages. /35/
MARINE...Cold front drifted in the coastal waters overnight and is anticipated to stall today. Light winds and some showers will be the main impact today but look for conditions to go downhill tomorrow as a developing surface low along the northeast TX coast begins to lift to the east-northeast. This low will deepen and the pressure gradient will tighten across the area with strong onshore flow (15-25kts) developing by midday tomorrow if not slightly earlier than that. As the surface low moves off to the northeast it will usher a strong cold front Sunday night and strong onshore winds will quickly become stronger offshore winds (20-25 kts possibly 30kts in the outer waters). We have issued a SCY for all of the coastal waters beginning tomorrow and persisting through Monday night. Winds should relax on Tuesday. /CAB/
AVIATION...(06z TAF Package)
Most terminals running MVFR (Marginal Visual Flight Rules) to VFR this evening as main convection has moved offshore. Still some elevated precipitation across northwest half of area and no indications of any lightning involved with this. Starting to see IFR ceilings sinking southward across KMCB, and will probably reach KBTR/KHDC/KASD by about 09z. Will be cutting way back on mention of precipitation in TAF set until at least 00z Sunday, and maybe even closer to 06z. Based on 00z MOS guidance from NAM and GFS, won't carry TSRA at any terminal for now. Morning IFR conditions should improve to MVFR (Marginal Visual Flight Rules) and potentially VFR prior to 18z. Conditions will again deteriorate from the west as we approach 06z Sunday, likely to upper end IFR. /35/.
NOAA New Orleans LA Office: Watches - Warnings - Advisories
LA...None. GM...Small Craft Advisory from 9am Sunday to 6am CST Tuesday for GMZ550-552-555-557-570-572-575-577.
Small Craft Advisory from noon Sunday to 6am CST Tuesday for GMZ536-538.
Small Craft Advisory from 3pm Sunday to 6am CST Tuesday for GMZ530-532-534.
MS...None. GM...Small Craft Advisory from 9am Sunday to 6am CST Tuesday for GMZ552-555-557-570-572-575-577.
Small Craft Advisory from noon Sunday to 6am CST Tuesday for GMZ538.
Small Craft Advisory from 3pm Sunday to 6am CST Tuesday for GMZ532-534.