In the overnight hours on May 17th into the early morning on May 18th, a cluster of slow moving severe thunderstorms associated with a weak mid-level disturbance drifted east across southeastern Louisiana. Ample overnight instability and weak steering flow resulted in damaging wind gusts, flash flooding and a few isolated weak tornadoes.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS LIX wrote it up.
In the overnight hours on May 17th into the early morning on May 18th, a cluster of slow moving severe thunderstorms associated with a weak mid-level disturbance drifted east across southeastern Louisiana. Ample overnight instability and weak steering flow resulted in damaging wind gusts, flash flooding and a few isolated weak tornadoes.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS New Orleans, LA wrote its last area forecast discussion before the first event at May 17, 3:06 PM CST, 2 hours 46 minutes earlier.
Area Forecast Discussion
National Weather Service New Orleans LA
406 PM CDT Mon May 17 2021
.SHORT TERM (Tonight through Wednesday Night)...A broad region of
difluence and increased upper level forcing will remain over
portions of the forecast area through Wednesday night. This region
of enhanced lift will interact with a plume of deep tropical
moisture and moderate instability feeding into the area to
produce periods of shower and thunderstorm activity. Precipitable
water values will remain high in excess of 1.75 inches across the
western half of the CWA, and light winds aloft will allow for slow
storm motion tonight through tomorrow night. There does appear to
be a period of lower instability tonight, and this is reflected
in lower POP values. Conditions will turn more favorable for
convective development from late morning through the afternoon
hours tomorrow as temperatures warm back into the upper 70s and
lower 80s. Given the slow storm motions anticipated and moist
adiabatic lapse rates in place, efficient and slow moving
thunderstorms could form. These warm and efficient rain processes
could produce rainfall rates in excess of 2 inches per hour, and
result in locally heavy rainfall over isolated areas. At this
time, the most likely areas for heavy rainfall appear to be
extending from a line generally south and west of Baton Rouge and
New Orleans, and a flash flood watch has been issued for this
region. The convective activity should begin to wane tomorrow
night as instability values decrease, and the threat of heavy
rainfall should begin to diminish. However, given the uncertainty
in exact timing, it was decided to keep the flash flood watch out
through Wednesday morning.
The main heavy rainfall axis should shift back to the west toward
Texas on Wednesday as a strengthening mid to upper level ridge
axis begins to exert greater influence over the forecast area.
Increasing upper level subsidence and a pool of drier air in the
mid-levels will begin to spread into the region from the east.
This will bring lower precipitable water values and slightly lower
rain chances to the area with a fairly sharp east to west POP
gradient in place. Temperatures will also begin to warm as ridging
builds in with highs warming from the upper 70s and lower 80s into
the mid 80s. The convection will be largely diurnal on Wednesday
with most of the activity diminishing in the evening hours.
.LONG TERM (Thursday through Sunday Night)...The ridge axis will
continue to build into the area with increasing subsidence and a
strong mid-level cap taking hold of most of the area. A sharp east
to west gradient in atmospheric moisture will be evident on
Thursday and Friday with higher POP values across the western
third of the CWA. Temperatures will continue to warm with highs
climbing into the mid to upper 80s on Thursday and Friday. By the
weekend, the high will be in firm control of the area with a
strong capping inversion and warmer than average temperatures in
the upper 80s and lower 90s expected. There could be some isolated
diurnal convection across the western third of the CWA where just
a bit more moisture and less influence of the ridge is expected.
Overall, a much drier and warmer pattern is expected to develop by
the weekend.
&&
.AVIATION...The 00z TAF will show lingering MVFR ceilings of
between 1500 and 3000 feet through the overnight hours at the
majority of the terminals with only KMCB dropping into IFR range
around 12z tomorrow. The rainfall should become less prevalent and
have only VCSH mention for most terminals. Another round of
showers and thunderstorms should begin to develop during the late
morning hours tomorrow and continue to develop through the
afternoon. Brief periods of IFR conditions could accompany these
thunderstorms.
&&
.MARINE...A tightening pressure gradient will bring increased
onshore flow to the area through the end of the week. Southeast
winds of 15 to 25 knots will produce rough seas due to a
combination of both wind waves and swell through Saturday. As a
result, small craft advisories are anticipated to continue over
the open Gulf waters and sounds through the end of the week. Tides
will also be higher along south and east facing shores and some
minor coastal flooding will be possible.
&&
.PRELIMINARY POINT TEMPS/POPS...
MCB 66 81 67 83 / 60 70 40 60
BTR 69 82 69 83 / 70 80 50 70
ASD 69 82 69 82 / 30 60 40 50
MSY 70 81 71 82 / 40 70 50 60
GPT 71 80 70 79 / 30 50 40 40
PQL 69 82 68 82 / 30 40 30 30
&&
.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Flash Flood Watch through Wednesday morning for LAZ034-046>050-
056>061-063>070-072-075>078.
Coastal Flood Advisory until midnight CDT Tuesday night for
LAZ076-078.
GM...Small Craft Advisory until 7 AM CDT Wednesday for GMZ536-538-550-
552-555-557-570-572-575-577.
MS...Coastal Flood Advisory until midnight CDT Tuesday night for
MSZ080.
GM...Small Craft Advisory until 7 AM CDT Wednesday for GMZ538-550-552-
555-557-570-572-575-577.
&&
PGThe national radar mosaic for the moment the first event began.
18 flash flood, 3 thunderstorm wind, 2 tornado, 1 lightning. Local standard time, as filed.
Roof peeled off a mobile home in the Dutch Town area off Highway 74. Time estimated from radar.
Lightning struck a home on El Ranchitos Avenue causing a gas line to ignite on a water heater.
Report of water entering at least one home near Jefferson and Airline highways.
Report of water entering the WVLA NBC Local 33 studio on Bluebonnet and Highway 427.
An underpass quickly flooded which resulted in one fatality in a car. Time estimated.
Highway 75 closed at Waterloo Drive due to high water across the road.
Report of water in a home near the intersection of Perkins Road and Pecue Lane.
Bluff road at C Braud Road closed due to high water across the road.
Tennyson Drive reported impassable with water starting to approach a couple of homes.
A vehicle crashed into a flooded canal leading to one fatality. One other remains missing.
Scholar Drive impassable due to water covering roads, blocking access to Bonaire Subdivision.
Magnolia Drive and Plantation Drive in St. Gabriel impassable due to high water.
Streets impassable due to high water in O'Neal Place Subdivision off O'Neal Lane. Water approaching some homes.
Chadsford Avenue impassable due to high water.
Report of St. George Fire Department conducting a high water rescue from a home in St. George.
A NWS storm survey found a few large trees roughly snapped near the base and leaning into houses, from east to west. Two more trees with shallow roots were also uprooted. The neighborhood had widespread small limbs down and tree debris. Based on the survey and radar imagery at the time, this seems to be thunderstorm wind damage associated with a decaying mesoscale convective vortex (mcv), or a large area of strong winds. The initial estimate of the wind speed was likely 75-85 mph. Time was estimated based on eye witness reports and radar.
A storm likely spawned a waterspout near the northshore of Lake Pontchartrain and moved onshore as a tornado near Guste Island around 2:50 AM CDT. The tornado tracked to the north-northwest across mainly uninhabited swamp lands about two miles west of the Tchefuncte River. Sporadic softwood and hardwood tree damage was noted on the eastern shore of the inlet. Additional damage was likely but it was inaccessible during the the storm survey. The damage that was viewable from the ground survey indicates an EF-0 tornado with estimated peak winds around 75 mph.
The tornado was also confirmed by KLIX radar data with a tornado debris signature evident as it was crossing the inlet at 2:53 AM CDT. The tornado quickly lifted around 2:55 AM as it approached the northern shore of this inlet.
A tornado touched down just north of the river and south of the airport in Kenner and took the roof off a large building. It was noted the roof material was severely corroded and rusted. The tornado moved north and convergence in downed trees was seen just to the east of a cemetery. The tornado continued to track north- northeast, with trees down near the railroad tracks and power lines down just north of the tracks, where it looks like the tornado lifted.
Numerous roads reported impassable in the Hahnville area.
Numerous roads reported impassable in the Norco area.
Numerous roads reported impassable in the Destrahan area.
Report of wind damage in Violet on South Lake Boulevard. Damage consists of some metal awnings and a patio cover along with a wooden gazebo lifted and moved. Several large oak tree branches also down.
Report of several streets impassable in across portions of New Orleans, mostly in the Uptown Area.
Numerous vehicles underwater across the southern part of East Baton Rouge parish from earlier flash flooding from heavy rain.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Flash Flood, East Baton Rouge | 2021-05-17 | 33 | Male | Vehicle/Towed Trailer | Direct |
| Flash Flood, West Baton Rouge | 2021-05-17 | 40 | Male | Vehicle/Towed Trailer | Direct |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Louisiana in 2021Every state in 2021This day in weather historyThe tornado archive for Louisiana, 2021Warnings in Louisiana, May 2021
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 960534, 960536, 960530, 960531, 960532, 960538, 960533, 960540, 960541, 960542, 960544, 960546, 960547, 960548, 960529, 960550, 960551, 960552, 960553, 960554, 960555, 960556, 960557, 960559.