[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT42 KNHC 041432
TCDAT2

TROPICAL STORM KAREN DISCUSSION NUMBER   6
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122013
1000 AM CDT FRI OCT 04 2013

AFTER BEING DISPLACED WELL EAST OF THE LOW-LEVEL CENTER OF KAREN...
DEEP CONVECTION HAS RECENTLY DEVELOPED A LITTLE CLOSER TO THE
CENTER OVER THE PAST HOUR OR TWO...BUT THE CYCLONE IS STILL BEING
AFFECTED BY 20-25 KT OF WESTERLY SHEAR AND DRY AIR BEING ADVECTED
INTO THE CYCLONE. THE LAST CENTRAL PRESSURE REPORTED BY THE
AIRCRAFT WAS 1003 MB...AND BASED ON THE LATEST ROUND OF AIRCRAFT
DATA THE INTENSITY HAS BEEN REDUCED TO 45 KT. THE ENVIRONMENT DOES
NOT LOOK FAVORABLE FOR SIGNIFICANT INTENSIFICATION...WITH MODERATE
SHEAR EXPECTED TO CONTINUE FOR THE NEXT DAY OR TWO. HOWEVER...IF
THE SHEAR DOES LESSEN...EVEN FOR A SHORT PERIOD OF TIME...DEEP
CONVECTION COULD RE-DEVELOP CLOSER TO THE CENTER AND ALLOW FOR SOME
INTENSIFICATION. IN ADDITION...BY 48 HOURS UPPER-LEVEL DIVERGENCE
AHEAD OF AN APPROACHING MID/UPPER-LEVEL TROUGH COULD ALLOW FOR SOME
STRENGTHENING. THE NEW NHC INTENSITY FORECAST HAS BEEN ADJUSTED
DOWNWARD AND SHOWS LITTLE CHANGE IN THE NEXT 24 HOURS AND A
STRENGTHENING TO 55 KT BY 48 HOURS.

THE INITIAL MOTION HAS BEEN WOBBLING BETWEEN 325 AND 330 DEGREES AT
ABOUT 9 OR 10 KT OVER THE PAST FEW HOURS. THE FUTURE TRACK WILL BE
QUITE SENSITIVE TO THE STRUCTURE OF KAREN OVER THE NEXT COUPLE OF
DAYS. IN THE SHORT TERM A WEAKER SHALLOWER SYSTEM WILL BE STEERED
MORE TOWARD THE LEFT BY THE LOW-LEVEL FLOW...WHILE A DEEPER MORE
VERTICALLY COHERENT CYCLONE WOULD TURN NORTHWARD MORE QUICKLY DUE
TO A MID-LEVEL RIDGE TO THE EAST. GIVEN THE CURRENT APPEARANCE OF
KAREN AND THE CONTINUED SHEAR...THE NHC TRACK HAS BEEN ADJUSTED A
LITTLE TO THE LEFT DURING THE FIRST 24 HOURS TOWARD THE UKMET AND
ECMWF MODELS...WHICH SHOW A WEAKER SYSTEM. ALL OF THE GUIDANCE
SHOWS A NORTHEASTWARD TURN IN 36 TO 48 HOURS...BUT WITH LARGE
DIFFERENCES IN THE LATITUDE AT WHICH THE TURN OCCURS AND
SIGNIFICANT SPREAD IN WHERE THE CENTER CROSSES THE COAST. AT 36
HOURS AND BEYOND THE NHC TRACK IS CLOSE TO THE ECMWF AND THE
MULTI-MODEL CONSENSUS...AND CLOSE TO THE PREVIOUS OFFICIAL
FORECAST. GIVEN THE LARGE SPREAD AND THE DEPENDENCE OF THE TRACK ON
THE STRUCTURE AND INTENSITY OF KAREN...CONFIDENCE IN THE DETAILS OF
THE TRACK FORECAST...AND THEREFORE THE DISTRIBUTION OF IMPACTS
ALONG THE COAST...IS LOW.

THE NOAA GULFSTREAM-IV JET SAMPLED THE ENVIRONMENT NEAR KAREN AND
OVER THE NORTHERN GULF OF MEXICO OVERNIGHT. THESE DATA WILL BE
INCORPORATED INTO THE 12Z MODEL CYCLE...AND HOPEFULLY IMPROVE THE
ANALYSIS OF THE ENVIRONMENT NEAR AND AHEAD OF THE STORM.

GIVEN THE WESTWARD SHIFT IN THE NHC TRACK...THE TROPICAL STORM
WARNING HAS BEEN EXTENDED WESTWARD TO MORGAN CITY LOUISIANA. GIVEN
THE WEAKENING TREND AND THE REDUCTION IN THE INTENSITY FORECAST...IT
HAS BECOME A LITTLE LESS LIKELKY THAT KAREN WILL REACH HURRICANE
STRENGTH. IF THESE TRENDS CONTINUE...THE HURRICANE WATCH COULD BE
CHANGED TO A TROPICAL STORM WATCH OR WARNING LATER TODAY.

FORECAST POSITIONS AND MAX WINDS

INIT  04/1500Z 25.6N  90.2W   45 KT  50 MPH
 12H  05/0000Z 26.6N  90.7W   45 KT  50 MPH
 24H  05/1200Z 27.7N  90.9W   45 KT  50 MPH
 36H  06/0000Z 28.6N  90.5W   50 KT  60 MPH
 48H  06/1200Z 29.8N  88.6W   55 KT  65 MPH
 72H  07/1200Z 33.5N  83.0W   25 KT  30 MPH...POST-TROP/EXTRATROP
 96H  08/1200Z...ABSORBED

$$
FORECASTER BRENNAN



This weather bulletin was brought to you by:
www.nashvilleweather.net