FXUS64 KLIX 111110 AFDLIX

Area Forecast Discussion National Weather Service New Orleans LA Issued by National Weather Service Jacksonville FL 610 AM CDT Wed Sep 11 2024

New AVIATION

SHORT TERM
(Today through Thursday Morning)
Issued at 346 AM CDT Wed Sep 11 2024

The short-term discussion will largely focus on details and impacts associated with Hurricane Francine as of early this morning. Follow nhc.noaa.gov for the latest track, location and intensity forecast information.

Current Analysis: Early this morning (3-4AM CT), infrared satellite illustrates deep convection/strong CDO collocated with a strengthening sfc low center with Francine in the northwestern Gulf. Recon data tonight has indicated steady strengthening in response with dropping SLP/increasing max sustained winds to now 90mph (as of the 1AM intermediate advisory). Many factors at play going on. One, the approaching shortwave trough over Texas/northern MX. This will 1) Influence forward motion by increasing speed and direction to the NE, 2) drive dry mid-level air from TX/MX east entraining into the system and 3) introduce increasing 850-300mb shear (moreso currently located over the TX/LA coast on north). Some of these factors are against intensification, but Francine has found a brief window to strengthen, with nocturnal CDO blowup favored by ample warm SST's right before greater dry air approaches( which is nearing very close to Francine, working into the Gulf over the TX coast per GOES-16 Ch 9 WV) and just displaced far enough away from greater 850-300mb shear to the north. If anything this downstream divergence has supported a rather healthy upper-level outflow channel, helping to evacuate convective cirrus anvil blowoff further supporting the ongoing strengthening. This healthy satellite presentation (subtle transverse cloud banding and symmetric canopy) will continue to be closely watched.

However...These conditions will likely not persist. Francine will encounter the shear (already seeing indications of mid-level low displacement/tilt), CDO will taper back and entrainment will win over with time. The questions are 1) How much more can Francine strengthen in the next 6-8 hours before unfavorable conditions win over? This is a balance game, and is difficult with downstream implications. That's why we have experts, and the NHC forecast will continue to reflect any changes/trends. Because overall, impacts will still be significant to many folks in our local area and will now spend the time discussing below.

DAMAGING WINDS: As Francine continues NE, making landfall (guidance average roughly late Wednesday afternoon/evening) and location likely being around the central LA coastline, a large swath of damaging winds, in excess of 50-80+mph will spread inland across the Atchafalaya basin. I know the public focus has been on slight/subtle eastward nudges and adjustments and yes, this would ultimately "nudge" what will likely be a very intense band of damaging straight line winds associated with the decaying eyewall.
Position (from the Atchafalaya basin including Baton Rouge, east to around Livingston Parish) has the potential to see this intense swath Wednesday evening/overnight that will cause widespread tree and powerline damage and very well could be life-threatening. The current Hurricane Warning in effect for portions of our CWA highlights the areas with greatest potential seeing life- threatening high winds, and should be taken very seriously.
Elsewhere (farther north across the Florida Parishes into SW MS)
the storm will slowly decay with time, with the remnant eye wall expanding with time as dry air works into the circulation. Winds will still have the *potential* to be damaging up along I-55 to SW MS, where winds upwards of 50-70mph will be possible again, mainly confined closest to the center and remnant eye wall. For areas east to the I-59 corridor, damaging winds will also be possible upwards of 50-70mph, but could be more confined to any (slow to advance east/training) convective band, likely to develop. Concern here is the dry air entrainment into these convective bands locally transferring high winds to the surface. I would not count out the risk of seeing damaging winds even far east across the MS coast. While gradient winds will be lighter, convective damaging winds should not be ignored.

COASTAL FLOODING: Persistent east sfc flow will continue to pile water into east-facing shorelines early this morning. With the approach of Francine, water will begin to pile up along coastal SE LA with time. We are approaching spring tides, which adds to the inundation threat for all locations (outside of the Hurricane Risk Reduction System in New Orleans). P-SURGE probability of greater than 5ft of inundation has increased, specifically around coastal MS (Waveland) up to 50-60%, 20-50% for NW Pontchartrain. Due to this, deterministic ranges have increased along portions of these areas. See the National Hurricane Center storm surge forecast values for specifics. Also, conditions will be slow to improve regardless of Francine passing and NW/W surface flow increasing early Thursday - residual flooding will remain a problem, especially as water will take a while to filter back out of Maurepas/Pontchartrain through the Rigolets. Those preparing for inundation potential need to be cognizant of lingering issues, including residual ponding/flooding for the next few days.

FLASH FLOODING: Widespread average totals are being messaged around 4-6" storm total precipitation. This is an areal average, and will vary greatly with a likely higher swath of totals (likely on the higher end, approaching 10-12"+ in any slow-moving training rain bands. This will be a major impact, but narrowing down small-scale bands (how intense, forward propagation and location) is impossible to narrow down this far ahead in time.
Eastward quadrant 850mb moisture transport from the SE to NW will align opposite to upwind propagation vectors to support slow- moving nearly stationary bands dumping torrential rainfall, with intense rain rates upwards of 3-5"/hr quickly leading to flash flooding - especially heightened risk due to saturated antecedent soil conditions from recent heavy rain. Those susceptible to flash flooding need to have a plan in place. Most of the flooding concerns will likely come overnight, making the threat especially dangerous and life-threatening. Those who are planning to travel, highly reconsider unless it's absolutely necessary and if you do, do NOT cross water covered roadways. You are putting yourself and first responders lives at risk.

TORNADOES: The introduction of both dry air entrainment into the circulation later today plus, increasing wind shear will greatly support a more notable tornado risk outside of typical isolated chances. Proximity soundings from the RAP quantify a degree of ECAPE (entrainment CAPE) in the NE quadrant in conjunction with increasing available low-level SRH will support marine tropical cells, likely confined to feeder bands/mesoscale convergent boundaries greater emphasizing lift. This will largely support cells with waterspouts nearing and coming onshore as tornadoes, heightened specifically along the immediate coast of SE LA and coastal MS. Brief, short-tracked tornadoes can be expected with the threat diminishing SW to NE throughout the night as the dry air works into the region. Please, have a reliable way to receive warnings overnight that will WAKE YOU UP. Have a safe place - center of your home, away from windows where you can briefly take shelter. Tropical tornadoes, while not very strong, can cause a swath of life-threatening damage (enhanced, narrow corridor of high winds 80-100mph) that can damage homes, topple trees and destroy mobile homes. Have a plan.

RIVERS: Will respond, but for now, RFC QPF out to 48hrs in forecasts DO NOT account for the likelihood of training/slow- moving bands (greater rain totals) - likely leading to some rivers seeing higher crests than currently forecast. It is urged for everyone that has interest along rivers typically see impacts from high water to refer to your local river forecast at water.noaa.gov.

We will continue to pass along the latest from the National Hurricane Center and expected impacts to our website: weather.gov/NewOrleans and will be active on social media @NWSNewOrleans. Continue to follow official sources (nhc.noaa.gov)
and tune in to local broadcast networks for the latest information as it comes across. For evacuation or shelter information, follow local government county/parish officials for information pertaining to your area. KLG
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