textproduct: New Orleans/Baton Rouge

KEY MESSAGES

Updated at 1036 PM CST Wed Dec 3 2025 1. An area of low pressure near the coast will bring widespread rain and embedded thunderstorms to the area Thursday morning through Saturday morning. 3-day rainfall totals will generally be 1.5" to 3" along the I-10/12 corridor with locally higher amounts as high as 6" especially west of I-55.

2. There is a marginal threat of excessive rainfall with this system particularly on Thursday where locally higher rain totals of 2" to 4" in a approximately 6 hour period could result in flash flooding of urban and poor drainage areas. Locally higher amounts upwards of 5" cannot be ruled out. Exact location of heaviest rainfall axis will be tied to the progress of the surface low and associated convection, but the Baton Rouge metro area appears to be the primary area of concern as it pertains to flooding of urban and poor drainage areas with this rainfall.

3. The slow-moving frontal boundary associated with this low will clear land areas Thursday night. Drier air filtering in will lower rainfall rates and reduce the risk for excessive rainfall and flash flooding. Additional rainfall of up to 3" could occur mainly along and east of the I-55 corridor. However, most areas are likely (>50%) to see between 0.5" and 1.5" with scattered shower activity Friday through Saturday.

SHORT TERM

(Tonight through Saturday) Issued at 1036 PM CST Wed Dec 3 2025

Warm front convection in association with a trough of low pressure near Corpus Christ, TX (as of 0300 UTC) has created a large area of showers and storms across SW LA and Vermillion Bay. Stratiform from this deepening convection continues to spread northeast and light rain will begin across western areas within the next couple of hours. Dew point temperatures remain in the 40s across most of the CWA, but the atmosphere is expected to moisten rapidly as the warm front encroaches on the LA coast early Thursday. The discrepancy in moistening between LIX (PWAT 0.81") and LCH (PWAT 1.45") 00 UTC soundings illustrates where each location was in this moistening process earlier tonight. Dew points will rise into the 50s to low 60s on the immediate coast and PWAT values will exceed the 90th percentile (1.52") and may approach daily maximum (1.92") as dry layers aloft mix out and yield a much more conducive environment for efficient rainfall rates exceeding 2" per hour.

Latest CAM guidance has overall trended faster with onset of rainfall, but remains in some disagreement regarding where the axis of heaviest rainfall will occur. HREF guidance is heavily skewed toward the aggressive NAM 3KM solution of a heavy band of rainfall stretching from Lake Charles through Donaldsonville later this morning while other guidance such as the RAP and HRRR suggest that heavier rainfall could be in the form of a band north of Baton Rouge and one closer to the Louisiana coast in association with the surface convergence of the surface trough. The latest forecast attempts to blend these solutions and focuses on heaviest rainfall occurring along the I-10/12 corridor in Louisiana on Thursday though additional revisions could be made as the event gets going later this morning. Gist is locally heavier rainfall with this convection could cause flash flooding of urban and poor drainage areas.

The surface trough will continue to push eastward across the coastal waters during the day Thursday and gradually take away additional surface forcing needed to sustain new convective development. Additionally, slightly drier air aloft will bring PWATs down closer to the 90th percentile and yield less efficient rainfall rates. This should gradually reduce the excessive rainfall risk from west to east across the area on Thursday evening into Friday morning. While the surface forcing mechanism will scoot off to the east, forcing aloft associated with persistent southwesterly flow of the longwave trough over the central CONUS will continue to provide enough lift to squeeze out showers and a couple of elevated storms on Friday into Saturday.

LONG TERM

(Saturday night through Wednesday night) Issued at 1036 PM CST Wed Dec 3 2025

The fire hose of rainfall will gradually taper off into Saturday night as a final shortwave trough lifts out with the broader longwave trough into the eastern CONUS and mid-upper flow pivots from southwest to northwest. This will allow for a more proper frontal passage on Sunday night and bring colder temperatures surface high pressure back across the area to start next week.

Model uncertainty remains regarding the next shot of cold air early next week, but the average forecast calls for temperatures near freezing for SW MS at this time. Additional attention will be brought to this if confidence increases in freezing conditions across more of the area in future forecast packages.

AVIATION

(06Z TAFS) Issued at 1036 PM CST Wed Dec 3 2025

-SHRA beginning to spread from west to east across terminals with VFR VIS/CIGs still prevailing for now. Winds remain light out of the east, but will intensify at MSY/NEW namely with wind off the lake with gusts upwards of 15 to 20 knots at times during the day Thursday. Widespread MVFR-IFR ceilings across all terminals starting roughly around 0900-1200 UTC Thursday and last through most of the day, potentially through the end of the forecast cycle. An area of low pressure will move across the northern Gulf Coast bringing periods of light to moderate rainfall from 10z through the end of this forecast cycle. There may be a few periods of heavier precipitation and reduced VIS/CIGs in which TSRA conditions are present. Highest chance of that occurring will be at BTR, MSY, HUM, and NEW. -SHRA will prevail through the end of the period and additional rounds of light to moderate rain will continue into Friday.

MARINE

Issued at 1036 PM CST Wed Dec 3 2025

A weak area of low pressure will gradually drift east across the Louisiana Coast on Thursday. This will tighten the pressure gradient especially east of the Mississippi River delta. Winds will increase with moderate to strong east-southeast to easterly winds. This will have multiple impacts with Small Craft Advisory conditions expected Thursday into Friday. Winds will relax and return to offshore late Friday and then more variable on Saturday with the passage of another weak sfc low. A frontal passage on Sunday night will bring another push of strong offshore winds on Monday which could prompt small craft headlines for much of the coastal waters.

In addition to the small craft impacts, the increase in onshore winds will combine with the increasing tidal cycle at the end of the week and lead to some minor coastal flooding. Main concern will be east facing shores of Orleans, St Bernard, Plaquemines, and far southeastern St Tammany. In addition coastal Hancock around Waveland will also deal with some minor coastal flooding Thursday night through Friday morning. The tide cycle will remain elevated into the weekend and additional minor coastal flooding cannot be ruled out. Additional headlines may be needed if the forecast high tide increases any further above 1 foot MHHW.

PRELIMINARY POINT TEMPS/POPS

MCB 55 42 49 44 / 0 90 100 100 BTR 59 46 55 47 / 0 90 100 90 ASD 58 43 57 47 / 0 80 90 90 MSY 60 51 62 53 / 0 80 90 90 GPT 57 45 57 49 / 0 60 90 90 PQL 57 41 56 47 / 0 50 90 90

LIX WATCHES/WARNINGS/ADVISORIES

LA...Coastal Flood Advisory from 6 PM Thursday to 6 AM CST Friday for LAZ070-076-078.

GM...Small Craft Advisory from 6 AM Thursday to 6 AM CST Friday for GMZ530-532-534-536-538-555-557-577.

MS...Coastal Flood Advisory from 6 PM Thursday to 6 AM CST Friday for MSZ086-087.

GM...Small Craft Advisory from 6 AM Thursday to 6 AM CST Friday for GMZ532-534-536-538-555-557-577.