MESO: Mesoscale Discussion 1834

ACUS11 KWNS 292018
SWOMCD
SPC MCD 292017
ALZ000-FLZ000-MSZ000-LAZ000-292045-

MESOSCALE DISCUSSION 1834
NWS STORM PREDICTION CENTER NORMAN OK
0317 PM CDT WED AUG 29 2012

AREAS AFFECTED...EXTREME E CENTRAL TO SERN LA...SRN MS AND FAR SWRN
AL

CONCERNING...TORNADO WATCH 594...

VALID 292017Z - 292045Z

THE SEVERE WEATHER THREAT FOR TORNADO WATCH 594 CONTINUES.

SUMMARY...THE TORNADO THREAT...ATTENDANT TO CONVECTIVE RAINBANDS
WITHIN THE N-E PERIPHERIES OF TROPICAL STORM ISAAC...WILL PERSIST
INTO THE EVENING ACROSS THE CURRENT TORNADO WATCH /#594/. THE
SLOWLY NWWD MOVING TROPICAL CYCLONE WILL ALSO RESULT IN A SMALL NWWD
EXPANSION OF THE TORNADO THREAT ACROSS SRN MS INTO EXTREME E CENTRAL
LA. AS SUCH...A NEW/REPLACEMENT TORNADO WATCH IS LIKELY...95%...
BEFORE THE SCHEDULED 21Z EXPIRATION OF WW 594.

DISCUSSION...AT 20Z...REGIONAL RADAR IMAGERY INDICATED THE CENTER OF
ISAAC WAS LOCATED IN SERN LA...APPROXIMATELY 30 NNW HUM OR 35 W
MSY...WITH TWO PRIMARY CURVED CONVECTIVE RAINBANDS. BOTH OF THESE
BANDS EXTENDED FROM NEAR AND OFFSHORE SERN LA AND SWRN AL...WITH ONE
BAND EXTENDING NNWWD INTO SERN TO SOUTH CENTRAL MS AND THE ADJACENT
LA PARISHES...WHILE THE SECOND BAND WAS A LITTLE FARTHER E EXTENDING
NNWWD THROUGH FAR SWRN AL /INCLUDING MOB/ INTO SERN MS TO THE NE OF
THE FIRST BAND.

ISAAC WILL CONTINUE TO TRACK SLOWLY TO THE NW RESULTING IN AN
INCREASE IN DEEP LAYER WIND FIELDS ACROSS EAST CENTRAL LA AND OVER
MORE OF SRN MS AS ALREADY SHOWN IN WFO-JAN WSR-88D DURING THE LAST
FEW HOURS...WITH AT LEAST 50 KT FROM JUST OFF THE SURFACE TO AROUND
4 KM AGL. DESPITE THIS NWWD TRACK...THE ERN EXTENT OF THE OUTER
BAND IS EXPECTED TO CONTINUE AFFECTING FAR SWRN AL...RESULTING IN
THIS REGION REMAINING IN A TORNADO THREAT INTO THE EVENING.
ANALYSIS OF AREA VADS AND ACCOUNTING FOR STORM MOTIONS CONTINUES TO
INDICATE SFC-1 KM SRH VALUES OF 200-300 M2/S2. GREATER INSTABILITY
IN PLACE THIS AFTERNOON ACROSS SWRN AL TO SERN MS /MUCAPE 1000-1500
J/KG/ HAS BEEN SUPPORTING STRONGER CONVECTION INTO THESE
REGIONS...WITH SOME UPDRAFTS BECOMING DEEP ENOUGH FOR LIGHTNING
PRODUCTION.

..PETERS/WEISS.. 08/29/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...MOB...JAN...LIX...LCH...

LAT...LON 28809003 29209028 29449010 30119081 30069140 30729196
31639198 32099160 32189031 32148953 31898853 31708829
31638803 31218781 31248765 30678739 30018716 29868735
29728818 29518835 29068848 28688873 28478929 28809003

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