Special Weather Statement, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
357 AM CDT Tue May 18 2021

.SHORT TERM (Today through Thursday Night) Not a lot of difference
in thought from earlier fcast. A broad wake low behind the
heaviest band of sh/ts will remain through 7am today with winds of
30-40mph and a few gusts up to 50mph possible. These winds can
easily bring trees and powerlines down with already saturated
soils. 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 through Wed. Conditions
will turn more favorable by daylight today for convective
development through the afternoon hours 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. Some of the higher rainfall totals through Wed could fall
over already flooded areas. As the rainfall extends northward,
more areas could fall under flooded conditions and the flash flood
watch will be extended northward as well.

The main heavy rainfall axis should shift back to the west toward
Texas by Wednesday afternoon 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. A strong
subsident inversion should keep things somewhat dry Thursday
allowing the area to finally dry up somewhat.

.LONG TERM (Friday through Monday 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 Friday
with higher POP values across the western third of the CWA. 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...Another round of showers and thunderstorms should begin
to develop during the late morning hours and continue to develop
through the afternoon. Brief periods of IFR conditions could
accompany these thunderstorms along with gusty winds from variable
directions depending on TS direction of approach.

&&

.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  78  67  82  67 / 100  30  70  20
BTR  81  69  84  69 / 100  50  90  30
ASD  80  70  82  70 / 100  50  70  20
MSY  81  72  84  73 / 100  60  80  30
GPT  80  71  81  70 /  80  40  50  20
PQL  80  69  81  68 /  60  30  30  10

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...High Wind Warning until 7 AM CDT this morning for LAZ034>037-039-
     046>050-056>061-065>068-071-072-075.

     Flash Flood Watch through Wednesday morning for LAZ034>037-039-
     046>050-056>061-063>072-075>078.

     Coastal Flood Advisory until midnight CDT tonight for LAZ076-078.

GM...Small Craft Advisory until 7 AM CDT Wednesday for GMZ536-538-550-
     552-555-557-570-572-575-577.

     Flash Flood Watch through Wednesday morning for GMZ530.

     Small Craft Advisory until 9 AM CDT this morning for GMZ530-534.

MS...High Wind Warning until 7 AM CDT this morning for MSZ068>071.

     Flash Flood Watch through Wednesday morning for MSZ068>071-077-
     080.

     Coastal Flood Advisory until midnight CDT tonight for MSZ080.

GM...Small Craft Advisory until 7 AM CDT Wednesday for GMZ538-550-552-
     555-557-570-572-575-577.

     Small Craft Advisory until 9 AM CDT this morning for GMZ534.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1059 PM CDT MON MAY 17 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1048 PM     FLASH FLOOD      1 NW OAK HILLS PLACE    30.38N 91.10W
05/17/2021                   EAST BATON ROUGE   LA   BROADCAST MEDIA

            WATER ENTERING THE WVLA STUDIO.

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE NEW ORLEANS LA
1108 PM CDT MON MAY 17 2021

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1107 PM     FLASH FLOOD      2 ESE OAK HILLS PLACE   30.36N 91.05W
05/17/2021                   EAST BATON ROUGE   LA   PUBLIC

            WATER IN A HOME NEAR THE INTERSECTION OF
            PERKINS RD AND PECUE LN. VIA SOCIAL MEDIA.

&&

DM

Special Weather Statement
National Weather Service New Orleans LA
107 AM CDT Tue May 18 2021

LAZ036-037-046>050-071-072-MSZ069-070-180815-
East Feliciana-St. Helena-Iberville-West Baton Rouge-
East Baton Rouge-Ascension-Livingston-Northern Tangipahoa-
Southern Tangipahoa-Amite-Pike-
Including the cities of Jackson, Clinton, Felps, Darlington,
Easleyville, Greensburg, Montpelier, Bayou Sorrel, Plaquemine,
White Castle, Port Allen, Addis, Brusly, Baton Rouge, Gonzales,
Donaldsonville, Prairieville, Denham Springs, Watson, Walker,
Amite, Kentwood, Roseland, Wilmer, Hammond, Robert, Ponchatoula,
Gillsberg, Gloster, Smithdale, Liberty, and McComb
107 AM CDT Tue May 18 2021

...STRONG WINDS IN THE WAKE OF THUNDERSTORMS...

Strong winds have developed in the wake of a complex of
thunderstorms across portions of southwest Mississippi and
southeast Louisiana early this morning. Wind gusts of 40 to 50 mph
have been observed in the Baton Rouge and McComb areas since
midnight. Winds this strong with wet ground from heavy rainfall
could cause damage from downed trees. These winds could also cause
problems for high profile vehicles, especially on Interstates 10
and 12. Winds should slowly diminish as the thunderstorms continue
to move east of the area.

Special Weather Statement
National Weather Service New Orleans LA
213 AM CDT Tue May 18 2021

LAZ066-180800-
Lower Terrebonne-
213 AM CDT Tue May 18 2021

...A STRONG THUNDERSTORM WILL AFFECT SOUTHEASTERN TERREBONNE
PARISH...

At 213 AM CDT, a strong thunderstorm was located 10 miles southwest
of Dulac, or 21 miles southwest of Houma, moving east at 40 mph.

Winds in excess of 40 mph are possible with this storm.

Locations impacted include...
Dulac, Montegut, Chauvin, Cocodrie, Tambour Bay Buoy and Lumcon
Center Buoy.

Torrential rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

LAT...LON 2922 9094 2922 9085 2920 9086 2923 9083
      2926 9090 2924 9095 2931 9092 2936 9098
      2950 9053 2932 9042 2927 9048 2928 9057
      2925 9059 2922 9053 2921 9057 2925 9061
      2921 9059 2922 9064 2914 9065 2911 9088
TIME...MOT...LOC 0713Z 257DEG 36KT 2930 9087

Special Weather Statement
National Weather Service New Orleans LA
247 AM CDT Tue May 18 2021

LAZ072-075-180815-
Northwest St. Tammany-Southern Tangipahoa-
247 AM CDT Tue May 18 2021

...A STRONG THUNDERSTORM WILL AFFECT WEST CENTRAL ST. TAMMANY AND
SOUTHEASTERN TANGIPAHOA PARISHES...

At 245 AM CDT, a strong thunderstorm, possibly containing a
waterspout was located over Lake Pontchartrain near Madisonville, or
8 miles southwest of Covington, moving north at 15 mph. If this
storm moves onshore, a Tornado Warning may be necessary.

Winds in excess of 40 mph are possible with this storm.

Locations impacted include...
Covington and Madisonville.

This includes Interstate 12 between mile markers 55 and 61.

LAT...LON 3036 9008 3037 9015 3039 9021 3033 9028
      3045 9033 3050 9013
TIME...MOT...LOC 0745Z 162DEG 13KT 3037 9020

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