Marine Weather and Tide Forecast for Mandeville, LA

SHORT TERM
(Now through Saturday night)
Issued at 135 PM CDT Wed Jun 17 2026

Tropical Storm Arthur will make landfall near the LA/TX border this evening. This system is highly sheared with the mid-level low expected to track further to the east across the Atchafalaya Basin and into the forecast area tonight. A strong mesoscale convective complex with heavy rainfall and threat of damaging wind gusts and a few tornadoes will accompany this mid-level low as it passes through the region. Conditions will turn a bit breezy as the low passes through with southerly winds of 10 to 20 mph with gusts of 25 mph developing tonight. This will lead to some minor coastal flooding issues around high tide for our south facing shorelines, particularly around Grand Isle, Port Fourchon, and the coastal communities of Terrebonne Parish. Above ground flooding of 1 to 2 feet is possible around high tide tonight.

Model sounding analysis indicates a highly favorable environment for both tornadoes and heavy rainfall to occur. PWATS will remain near the daily max tonight into tomorrow and 500mb temperatures will range near -5C through tomorrow. These warm temperatures aloft will support very warm and highly efficient rain processes that in turn will produce rainfall rates of 3 to 4 inches per hour as the mesoscale convective complex moves through the region overnight. This will lead to a corridor, most likely from the River Parishes and Baton Rouge metro northeast into the Northshore and coastal Mississippi, of very high rainfall totals that could approach 10 inches in a few locations. These high rainfall totals on top of already saturated soils will quickly lead to considerable and life-threatening flash flooding concerns tonight into tomorrow morning. The threat of widespread flash flooding will diminish by the afternoon as the mid-level low pulls into Alabama and more typical Summer afternoon convection redevelops with daytime heating.

The tornado threat will peak between 9pm and 8 am as the mid-level moves through the area and directional shear increases dramatically. 0-3km SRH values will rise to between 250 and 350m2/s2 close to midnight, and several mini-supercells should form on the leading flank of the mesoscale convective complex tonight from late this evening into the early morning hours. Areas from the River and Bayou Parishes, metro New Orleans, the Northshore, and coastal Mississippi have the highest probabilities of tornadic development, but the entire area will be under threat tonight.

Conditions will greatly improve as we move into tomorrow night and rest of the short term period in terms of the heavy rainfall threat. A broad deep layer ridge axis will expand northward across the Gulf South resulting in lower overall rain chances as we move into Friday and Saturday, but the side-effect will be significantly warmer temperatures. Highs will easily climb into the low to mid 90s and very high dewpoints in the upper 70s and lower 80s will produce heat index readings of around 110 degrees both days. A heat advisory will likely be issued for much of the area by tomorrow. Ample instability will accompany these warm temperatures with MLCAPE of 2000 to 2500 J/KG both days. As a result, diurnally induced convection will form each day with the highest probabilities north of I-12 where the influence of the mid to upper level ridge will be lower. Although PWATS will fall to more average levels by Saturday, the wet antecedent conditions could lead to isolated flash flooding incidents as rainfall rates still average 1 to 2 inches per hour.

LONG TERM
(Sunday through Tuesday night)
Issued at 135 PM CDT Wed Jun 17 2026

The influence of the ridge will grow as we move into next week with lower overall rain chances and continued warm temperatures.
Highs will easily continue to climb into the low to mid 90s each day and overnight lows will only cool into the upper 70s and lower 80s. Heat index values will continue to rise to between 105 and 110 degrees, so more days of heat advisory conditions can be expected. The growing influence of the ridge will lead to a strong mid-level capping inversion and overall lower rain chances from Sunday through Tuesday with only isolated to widely scattered afternoon showers and storms anticipated. Rain chances will be highest over the northern third of the forecast area where the capping inversion will be slightly weaker.

AVIATION
(00Z TAFS)
Issued at 618 PM CDT Wed Jun 17 2026

Conditions currently at VFR to MVFR as scattered showers and a few thunderstorms transit the area from south to north. Tropical Storm Arthur and its remnants will continue to bring impacts to the area with rain and gusty winds through the night. The most impactful weather will move through the area generally from 06Z to 15Z with BTR/MSY/HDC/MCB targeted from 06Z to 12Z and ASD/NEW/GPTfrom 09Z to 15Z. Brief periods of wind shear gusts to 20+ knots will accompany the strongest weather.

MARINE
Issued at 135 PM CDT Wed Jun 17 2026

Tropical Storm Arthur will make landfall near the border of Louisiana and Texas tonight. Strong southerly winds of 20 to 25 knots with gusts of 30 knots will remain in place over the coastal waters through tonight and into tomorrow and seas of 6 to 9 feet can be expected in the open Gulf waters. Small craft advisories remain in effect due to these conditions. Moving into the weekend and early next week, a broad area of high pressure will build back over the eastern Gulf waters. Persistent onshore winds of 10 to 15 knots and seas of 2 to 4 feet can be expected from Friday through early next week.

LIX WATCHES/WARNINGS/ADVISORIES
LA...Flood Watch through Friday morning for LAZ034>037-039-046>048- 056>058-064-071-076>087-089-090-092-094-096-098>100.

Coastal Flood Advisory until midnight CDT tonight for LAZ091-093- 095-097.

GM...Small Craft Advisory until 6 AM CDT Friday for GMZ529-531>536- 541-543-551-553-554-557-570-572-575-577.

MS...Flood Watch through Friday morning for MSZ068>071-077-083>088.

GM...Small Craft Advisory until 6 AM CDT Friday for GMZ531>536-541- 543-551-553-554-557-570-572-575-577.