Marine Weather and Tide Forecast for Grand Isle, LA

LONG TERM
(Sunday through Wednesday night)
Issued at 247 PM CDT Thu Apr 17 2025

A vigorous shortwave trough will eject out of the southern Plains and into the Midwest Sunday into Monday, and this will drive a frontal boundary toward the forecast area over this period. As the front moves into the area, the parent trough axis will quickly pull to the northeast and a prevailing southwesterly flow pattern will develop in the mid to upper levels. The end result will be the front stalling across the area on Monday and then lingering over the region through Wednesday. This pattern will bring a more unsettled weather pattern to the area as the front serves as a focusing mechanism for shower and thunderstorm development.

Sunday into Sunday night will be largely dry with only isolated shower and thunderstorm activity expected for areas generally north of I-10 and west of I-55. This region of the forecast area will have the weakest capping aloft and just enough forcing associated with the approaching trough and front to drive some convective development. Otherwise, it a warm and muggy day with highs climbing back into the mid 80s and lows only dipping to around 70.

Monday will see the highest probability of shower and thunderstorm activity as the aforementioned shortwave trough slides through the region. Fortunately, shear profiles will remain weak. This will keep any convective activity on the weaker side with the main concerns being brief heavy downpours and lightning strikes. Coverage will be fairly decent, especially north of I-10, as periods of showers and thunderstorms move through. By Monday night, the convective activity will shift to the east with only isolated to widely scattered convection. This is due to the trough axis departing to the east and some weak upper level negative vorticity and dry air advection in the mid and upper levels taking hold. Temperatures will also be slightly cooler with lows falling into the mid to upper 60s.

Tuesday and Wednesday will see a series of weak upper level impulses embedded within the broader southwest flow pattern pass through the region. These impulses will interact with the dissipating front stalled over the region to produce diurnal convective activity each day. At this time, the boundary looks to be stalled over the northern half of the CWA, and PoP values are highest for this area. Temperatures will also be near to slightly above average both days, but record heat is no longer anticipated due to the increased cloud cover and convection.

AVIATION
(06Z TAFS)
Issued at 1142 PM CDT Thu Apr 17 2025

VFR conditions will prevail for the vast majority of the forecast period. Only possible impacts could be some MVFR in the early morning for some patchy fog for BTR/MCB, and the next chance is lower ceilings right at the end of the forecast cycle. Otherwise it will be a bit blustery during the day with south to southeasterly with some gusts up to 20 to 25 knots possible. -BL

MARINE
Issued at 247 PM CDT Thu Apr 17 2025

A gradually tightening pressure gradient between a ridge over the northern Gulf and a low deepening over the southern Rockies and Plains will allow for increased winds starting tonight and continuing through Sunday. These winds will climb to between 15 an 20 knots in the open Gulf waters and close to 15 knots in the sounds and tidal lakes. Additionally, a decent fetch across the Gulf will allow 1 to 2 feet of swell to add onto the wind waves offshore, leading to seas of 6 to 8 feet over the weekend. These conditions will produce fairly rough sea states on Saturday and Sunday. The pressure gradient will ease on Monday as the low pulls to the northeast, and this will allow onshore winds to fall back below 10 knots. Seas will also gradually decrease to 2 to 3 feet by Tuesday evening.

PRELIMINARY POINT TEMPS/POPS
MCB 61 87 65 85 / 0 0 0 0 BTR 65 88 69 86 / 0 0 0 0 ASD 64 83 68 83 / 0 0 0 0 MSY 67 83 70 83 / 0 0 0 0 GPT 65 78 69 79 / 0 0 0 0 PQL 63 79 66 79 / 0 0 0 0

LIX WATCHES/WARNINGS/ADVISORIES
LA...None.
GM...None.
MS...None.
GM...None.