textproduct: New Orleans/Baton Rouge

KEY MESSAGES

Updated at 545 AM CDT Fri Sep 11 2026

- Deep tropical moisture moving into the area is causing localized heavy rainfall and flooding across urban parts of the I-10/12 corridor.

- This elevated risk for localized heavy rainfall leading to street flooding and overflowing of poor drainage will continue on Friday and into Saturday.

SHORT TERM

(Now through Monday) Issued at 119 AM CDT Fri Sep 11 2026

Rinse and repeat is the name of the game for today and tomorrow as a slow moving upper level trough axis slides through the Lower Mississippi Valley and Gulf South. A plume of deep tropical moisture will remain over the area through the period with PWATS running between the 90th percentile and daily max for mid- September both days. As temperatures warm into the mid to upper 80s, enough instability, as noted by SBCAPE of over 1000 J/KG, will be in place to support convective updraft development. Multiple rounds of shower and thunderstorm activity will develop in the vicinity of a weakening low centered over coastal Louisiana and then spread inland through the afternoon hours. Rainfall rates of 2 to 3 inches per hour will be common and storm motion will be 5 to 10 mph each day. The end result will be continued potential for localized flooding rainfall events to occur if storms become anchored and backbuild on weak mesoscale boundaries like the lakebreeze or seabreeze. If this occurs, these localized spots could easily see 3 to 5 inches of rainfall fall in short period of time. More urbanized areas with poor drainage or that are low lying will have the greatest impacts in the form of street flooding from these heavy rainfall events. Overall, the flooding will remain isolated and the region remains in a level 1 out of 5, marginal, risk of flash flooding today and tomorrow.

The upper level trough axis will shift to the east as we move into Sunday and Monday and a broad upper level high will start to shift toward the region from the west. As this high becomes more centered over the area, increasing negative vorticity advection and subsidence in the mid and upper levels of the atmosphere will lead to both drying and warming aloft. PWATS will fall to between the 75th and 90th percentile on Sunday and then further drop to between the median and 75th percentile by Monday. The lack of deep layer forcing aloft and weaker mid-level lapse rates will also help to inhibit convective development a bit. Any convection will tend to fire up more in the afternoon hours as temperatures climb into the lower 90s and the convective temperature is reached. The convection will also be more confined to pre-existing meso-scale boundaries like the seabreeze or remnant outflow boundaries resulting in more scattered coverage for both Sunday and Monday. Overall, a return to a more typical late Summer weather regime is expected as we move into the new week.

LONG TERM

(Monday night through Thursday) Issued at 119 AM CDT Fri Sep 11 2026

By Monday night, upper level ridging is expected to be centered over Tennessee, and is forecast to stay in the same general area through next Thursday. Surface high pressure over the Appalachians will extend southwestward into the area. Forecast soundings indicate that moisture should be sufficient for at least isolated to scattered afternoon convection each day. If there's a day where most areas would be dry (and hot), it'd probably be Tuesday.

This will bring us back to the summer pattern of afternoon temperatures in the low to mid 90s and 30-50% PoPs in the afternoons. These highs temps are about 5 degrees above normal for the end of summer and combined with the humidity will put heat index values in the 105-110 range, especially Tuesday, so advisories can't entirely be ruled out.

AVIATION

(12Z TAFS) Issued at 545 AM CDT Fri Sep 11 2026

Saturated soils and a weak surface based inversion associated with a rain cooled airmass from earlier in the night has allowed low stratus and fog to develop at several of the terminals over the past few hours. LIFR fog and stratus are impacting BTR, HDC, MCB, and ASD with MVFR conditions noted at HUM and NEW. These conditions will linger through 13-14z before quickly lifting as temperatures warm and boundary layer mixing increases. There have been some passing showers at GPT over the past few hours. These showers are forming on the east side of a weak low over southeast Louisiana and will continue to form for the next few hours. PROB30 wording is in place through 15z to reflect the passing convection. The remainder of the terminals will see a mix of MVFR and VFR conditions as a cumulus field ranging between 2000 and 3500 feet forms. Additional rounds of showers and thunderstorms will then develop over the area and impact all of the terminals between 17z and 00z with periods of lightning, gusty winds, and reduced visibilities. After 00z, convection will quickly wane with the loss of daytime heating and prevailing VFR conditions will take hold.

MARINE

Issued at 119 AM CDT Fri Sep 11 2026

A weak area of low pressure will dissipate over the area today with light and variable winds of 10 knots or less expected. Tomorrow, winds will turn more south-southwesterly at 10 to 15 knots as a broad surface high over Florida becomes more dominant. These conditions will persist into Saturday. The high will become more centered over the eastern Gulf and southeastern United States as we move into next week, and this will cause winds to turn more south- southeasterly at 5 to 10 knots from Sunday onward. Seas will generally remain in the 1 to 3 feet range with the highest seas well offshore. Additionally, thunderstorm activity will develop each day, peaking in the early to mid-morning hours, and these storms will produce higher wind gusts, waterspouts, and lightning concerns.

LIX WATCHES/WARNINGS/ADVISORIES

LA...None. GM...None. MS...None. GM...None.