Marine Weather and Tide Forecast for Grand Isle, LA

SHORT TERM
(This afternoon through Tuesday)
Issued at 1132 AM CDT Sun Mar 8 2026

Biggest concern in the short term will be development of fog tonight. Probabilistic guidance is indicating fairly high probabilities of dense fog, especially east of I-55 and along/north of I-10/12. Given the high dewpoints area-wide and the amount of rain that fell across the northwestern portions of the area, think the threat of at least patchy dense fog is there area- wide and have issued a dense fog advisory for all of SE LA and S MS from 1am through 9am Monday. Main argument against widespread fog is cloud cover which will limit cooling, but with dewpoints in the mid to upper 60s area-wide and afternoon temperatures not likely to rise much higher than the lower 70s, it won't take a substantial amount of cooling to reach the dewpoint temperature.

Moving on to rain chances... As showers and a couple isolated storms move out of the area this afternoon, dense cloud cover should limit redevelopment, though a few isolated to widely scattered showers cannot be ruled out. Better chances come again tomorrow afternoon as daytime heating provides sufficient instability and lift to fire off additional scattered showers and storms, mainly along/north of I-55 closer to the stalled frontal boundary.

Temperatures will remain well above normal for this time of the year with lows struggling to drop into the mid 60s and highs near or just above 80 degrees Monday, and in the low to mid 80s Tuesday.

LONG TERM
(Wednesday through Saturday)
Issued at 1132 AM CDT Sun Mar 8 2026

Warmer than normal conditions continue into Wednesday. Some uncertainty regarding exactly how warm it will get on Wednesday, though, given influx of cloud cover ahead of an approaching cold front and then showers/storms moving into the area at some point in the afternoon.

Bigger concern will be the thunderstorm threat along/ahead of the front. By Wed afternoon model forecast soundings indicate CAPE near or exceeding 1000 J/kg across most of the area as daytime heating destabilizes the atmosphere. With the mid/upper level trough moving into the lower MS Valley, and enhanced lift along the boundary, expect to see a squall line moving through the area mainly from late afternoon Wednesday and through the overnight hours. A little too soon to say with any certainty whether shear and instability will be sufficient to result in an organized severe weather threat, but some of the ingredients certainly look to be in place, and if the trend in the location/strength of the low level jet becomes even just a bit more favorable, it would support a greater severe weather threat. For the time being, the storm prediction center has highlighted a 15% severe weather threat area roughly across areas north of a line from Baton Rouge to Tylertown, and this seems to be a good starting point as the specifics continue to become clearer over the coming days.

In the wake of the cold front, a much cooler and drier airmass will move into the area for a few days. But even with the significant cool down, temperatures are forecast to be near or warmer than normal.

AVIATION
(00Z TAFS)
Issued at 639 PM CDT Sun Mar 8 2026

VFR conditions for most terminals over the next couple of hours before VIS/CIG reductions begin. Areas of dense fog will be likely across the terminals with IFR or lower conditions taking shape after 06z tonight. These conditions will improve by Monday afternoon with all local terminals seeing VFR from then through the end of the cycle. Southerly winds will remain light through the period. (Frye)

MARINE
Issued at 1132 AM CDT Sun Mar 8 2026

Isolated to scattered showers and a few thunderstorms will affect the coastal waters this afternoon but should dissipate this evening. Onshore flow will persist through midweek, strengthening to around 15 knots Wednesday ahead of a cold front. Showers and thunderstorms will accompany the front as it moves through the coastal waters Wednesday evening into the overnight hours. In the wake of the front, winds will turn offshore and strengthen with potential for gale conditions Wednesday night through at least Thursday morning before winds gradually begin to ease Thursday afternoon.

LIX WATCHES/WARNINGS/ADVISORIES
LA...Dense Fog Advisory from 1 AM to 9 AM CDT Monday for LAZ034>037- 039-046>048-056>060-064>071-076>090.

GM...Dense Fog Advisory from 1 AM to noon CDT Monday for GMZ530-532- 534-536-538-550-552-555-557.

MS...Dense Fog Advisory from 1 AM to 9 AM CDT Monday for MSZ068>071- 077-083>088.

GM...Dense Fog Advisory from 1 AM to noon CDT Monday for GMZ532-534- 536-538-550-552-555-557.