WTNT43 KNHC 012342
TCDAT3
 
TROPICAL DEPRESSION THIRTEEN SPECIAL DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132011
700 PM CDT THU SEP 01 2011
 
SATELLITE...SURFACE...AND NOAA RECONNAISSANCE AIRCRAFT DATA INDICATE
THAT THE LOW PRESSURE AREA OVER THE CENTRAL GULF OF MEXICO HAS
ACQUIRED A CLOSED CIRCULATION THAT IS DEFINED ENOUGH TO BE
CONSIDERED A TROPICAL DEPRESSION.  HOWEVER...THE CENTRAL REGION
STILL CONSISTS OF A LARGE AREA OF LIGHT WINDS.  THE AIRCRAFT DATA
AND BUOY OBSERVATIONS SUPPORT AN INITIAL INTENSITY OF 30 KT.
ALTHOUGH THERE IS WIND SHEAR OVER THE CYCLONE...AN UPPER-LEVEL
ANTICYCLONE IS FORECAST TO BUILD OVER THE GULF OF MEXICO DURING THE
NEXT DAY OR SO.  THIS SHOULD PROVIDE A MORE FAVORABLE UPPER-LEVEL
ENVIRONMENT FOR STRENGTHENING.  HOWEVER...SINCE THE CIRCULATION IS
LARGE ONLY GRADUAL STRENGTHENING IS ANTICIPATED.  THE OFFICIAL
INTENSITY FORECAST FOLLOWS THIS REASONING AND IS CLOSE TO THE
SHIPS/LGEM GUIDANCE.
 
SINCE THE DEPRESSION IS IN ITS FORMATIVE STAGE THE INITIAL MOTION
IS HIGHLY UNCERTAIN.  IN FACT...THE CENTER COULD REFORM WITHIN THE
LARGE CIRCULATION DURING THE NEXT 12-24 HOURS.   THE DEPRESSION IS
CURRENTLY LOCATED TO THE SOUTH OF A MID/UPPER LEVEL RIDGE OVER THE
CENTRAL UNITED STATES.  THE RIDGE IS FORECAST TO SLIDE EASTWARD AND
WEAKEN DURING THE NEXT 2-3 DAYS...LEAVING THE CYCLONE IN WEAK
STEERING FLOW.  THE OFFICIAL FORECAST SHOWS A SLOW NORTHWESTWARD
MOTION DURING THE NEXT 24 HOURS...FOLLOWED BY A TURN TOWARD THE
NORTH AND NORTHEAST.  THE NHC TRACK IS IN BEST AGREEMENT WITH THE
GFS AND ECMWF MODELS.
 
THE DEPRESSION IS EXPECTED TO MOVE VERY SLOWLY DURING THE NEXT 5
DAYS PROLONGING THE PERIOD OF TROPICAL STORM CONDITIONS AND HEAVY
RAINFALL OVER PORTIONS OF THE NORTHERN GULF COAST.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  02/0000Z 26.6N  91.4W   30 KT  35 MPH
 12H  02/0600Z 27.5N  92.3W   35 KT  40 MPH
 24H  02/1800Z 28.2N  92.6W   40 KT  45 MPH
 36H  03/0600Z 28.7N  92.7W   45 KT  50 MPH
 48H  03/1800Z 29.3N  92.6W   50 KT  60 MPH
 72H  04/1800Z 30.1N  92.3W   40 KT  45 MPH...INLAND
 96H  05/1800Z 31.1N  91.5W   30 KT  35 MPH...INLAND
120H  06/1800Z 32.0N  90.5W   25 KT  30 MPH...INLAND
 
$$
FORECASTER BROWN/AVILA
 

WTNT43 KNHC 020240
TCDAT3
 
TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132011
1000 PM CDT THU SEP 01 2011
 
ALTHOUGH THE OVERALL SATELLITE PRESENTATION OF THE DEPRESSION HAS
CHANGED LITTLE THIS EVENING...NEW BANDS OF DEEP CONVECTION HAVE
DEVELOPED TO THE SOUTHEAST OF THE CENTER.  SATELLITE
CLASSIFICATIONS AND RECENT BUOY OBSERVATIONS SUPPORT KEEPING THE
INITIAL INTENSITY AT 30 KT.  A NOAA HURRICANE HUNTER AIRCRAFT IS
SCHEDULED TO INVESTIGATE THE CYCLONE OVERNIGHT.  A SHEAR ANALYSIS
FROM UW-CIMSS SHOWS ABOUT 20 KT OF WESTERLY SHEAR OVER THE
CYCLONE.  THIS SHEAR IS FORECAST TO RELAX DURING THE NEXT 12-24
HOURS AS AN UPPER-LEVEL ANTICYCLONE BUILDS OVER THE GULF.  THIS IS
EXPECTED TO RESULT IN A FAVORABLE ENVIRONMENT FOR INTENSIFICATION.
HOWEVER...GIVEN THE LARGE SIZE OF THE CIRCULATION...STRENGTHENING 
IS EXPECTED TO BE GRADUAL.  THE NEW NHC INTENSITY FORECAST IS
NEARLY IDENTICAL TO THE PREVIOUS ADVISORY AND IS A BLEND OF THE
SHIPS/LGEM GUIDANCE.

THE DEPRESSION HAS NOT MOVED MUCH THIS EVENING...AND THE HIGHLY
UNCERTAIN INITIAL MOTION IS 315/2 KT.   SINCE THE DEPRESSION IS
STILL IN THE FORMATIVE STAGE...THE CENTER COULD REFORM WITHIN THE
LARGE CIRCULATION DURING THE NEXT 12-24 HOURS.  THIS POSSIBILITY 
IS SUPPORTED BY THE GFS...WHICH SHOWS THE CENTER REFORMING FARTHER
NORTH WITHIN 24 HOURS.  STEERING CURRENTS ARE EXPECTED TO REMAIN
WEAK DURING THE NEXT SEVERAL DAYS AS THE DEPRESSION REMAINS TO THE
SOUTH OF A WEAKENING MID/UPPER LEVEL RIDGE.  AS THE RIDGE SLIDES
EASTWARD...IT SHOULD ALLOW THE CYCLONE TO MOVE SLOWLY NORTHWARD...
THEN NORTHEASTWARD.  ALTHOUGH THE DYNAMICAL MODELS SHOWS LITTLE
OVERALL MOTION DURING THE NEXT 2-3 DAYS...THERE IS A LARGE SPREAD
IN THE GUIDANCE AND LOWER THAN NORMAL CONFIDENCE IN THE TRACK
FORECAST.  THE UPDATED NHC TRACK IS A LITTLE SLOWER AND EAST OF 
THE PREVIOUS FORECAST. 
 
THE SLOW MOTION OF THE CYCLONE DURING THE NEXT 5 DAYS IS LIKELY
TO PRODUCE A PROLONGED PERIOD OF TROPICAL STORM CONDITIONS AND
HEAVY RAINFALL OVER PORTIONS OF THE NORTHERN GULF COAST.

 
FORECAST POSITIONS AND MAX WINDS
 
INIT  02/0300Z 26.6N  91.5W   30 KT  35 MPH
 12H  02/1200Z 27.5N  92.2W   35 KT  40 MPH
 24H  03/0000Z 28.0N  92.4W   40 KT  45 MPH
 36H  03/1200Z 28.6N  92.4W   45 KT  50 MPH
 48H  04/0000Z 29.2N  92.3W   50 KT  60 MPH
 72H  05/0000Z 29.7N  92.1W   50 KT  60 MPH...NEAR THE COAST
 96H  06/0000Z 30.5N  91.5W   35 KT  40 MPH...INLAND
120H  07/0000Z 31.5N  90.0W   25 KT  30 MPH...INLAND
 
$$
FORECASTER BROWN
 

WTNT43 KNHC 020838
TCDAT3
 
TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132011
400 AM CDT FRI SEP 02 2011

SATELLITE IMAGERY...SURFACE OBSERVATIONS...AND AN EARLIER ASCAT
OVERPASS INDICATE THAT TROPICAL DEPRESSION THIRTEEN HAS A ELONGATED
CENTER OF CIRCULATION...WITH THE ELONGATION CURRENTLY FROM
EAST-NORTHEAST TO WEST-SOUTHWEST.  THE ASSOCIATED CONVECTION IS
CURRENTLY POORLY ORGANIZED...ALTHOUGH A STRONG BURST HAS RECENTLY
FORMED NEAR THE EAST-NORTHEASTERN END OF THE CENTER.  THE INITIAL
INTENSITY REMAINS 30 KT BASED ON THE ASCAT OVERPASS AND REPORTS
FROM OIL RIGS IN THE NORTHERN GULF.  WHILE THERE IS GOOD OUTFLOW
OVER THE EASTERN SEMICIRCLE...AN UPPER-LEVEL TROUGH IS PRESENT OVER
THE WESTERN SIDE OF THE CIRCULATION.

THE DEPRESSION HAS NOT MOVED MUCH DURING THE PAST SEVERAL HOURS...
WITH THE INITIAL MOTION A HIGHLY UNCERTAIN 315/2.  THE CYCLONE IS
CURRENTLY IN AN AREA OF LIGHT STEERING CURRENTS SOUTH OF A
MID-LEVEL RIDGE OVER THE MISSISSIPPI VALLEY.  THE DYNAMICAL MODELS
FORECAST THIS RIDGE TO MOVE EASTWARD AND WEAKEN AS A DEEP-LAYER
TROUGH MOVES SOUTHEASTWARD INTO THE OHIO VALLEY.  THIS EVOLUTION
SHOULD ALLOW THE DEPRESSION TO MOVE SLOWLY NORTHWESTWARD TO
NORTHWARD FOR THE NEXT 24-36 HR...FOLLOWED BY A GRADUAL TURN TOWARD
THE NORTHEAST.  MOST OF THE DYNAMICAL MODELS NOW SHOW THIS
SCENARIO...ALTHOUGH THERE REMAINS ENOUGH DISAGREEMENT BETWEEN THEM
TO KEEP THIS A LOW CONFIDENCE FORECAST.  THE NEW FORECAST TRACK IS
ADJUSTED SOUTH AND EAST OF THE PREVIOUS FORECAST BASED MAINLY ON
THE INITIAL POSITION...AND LIES CLOSE TO THE VARIOUS CONSENSUS
MODELS FOR THE FIRST THREE DAYS OF THE FORECAST.  IT SHOULD BE
NOTED THAT REFORMATIONS OF THE CENTER COULD CAUSE ERRATIC MOTION
AND ADJUSTMENTS TO THE FORECAST TRACK DURING THE NEXT COUPLE OF
DAYS.

THE CURRENT INTERACTION WITH THE UPPER-LEVEL TROUGH IS FORECAST BY
THE DYNAMICAL MODELS TO CONTINUE FOR AT LEAST THE NEXT COUPLE OF
DAYS...RESULTING IN VERTICAL WIND SHEAR CONDITIONS THAT...AT
BEST...WILL BE MARGINALLY FAVORABLE FOR INTENSIFICATION.  THIS
INTERACTION...COMBINED WITH THE CURRENT ORGANIZATION OF THE
SYSTEM...SUGGESTS THAT STRENGTHENING SHOULD BE SLOW.  THE NEW
INTENSITY FORECAST IS UNCHANGED FROM THE PREVIOUS ADVISORY AND LIES
BETWEEN THE STRONGER SHIPS AND WEAKER LGEM MODELS.
 
THE LARGE SIZE AND SLOW MOTION OF THE CYCLONE DURING THE NEXT 5 DAYS
IS LIKELY TO PRODUCE A PROLONGED PERIOD OF TROPICAL STORM
CONDITIONS AND HEAVY RAINFALL OVER PORTIONS OF THE NORTHERN GULF
COAST.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  02/0900Z 26.5N  91.7W   30 KT  35 MPH
 12H  02/1800Z 27.0N  92.1W   35 KT  40 MPH
 24H  03/0600Z 27.6N  92.3W   40 KT  45 MPH
 36H  03/1800Z 28.2N  92.2W   45 KT  50 MPH
 48H  04/0600Z 28.8N  92.0W   50 KT  60 MPH
 72H  05/0600Z 29.5N  91.5W   50 KT  60 MPH...INLAND
 96H  06/0600Z 30.5N  90.0W   40 KT  45 MPH...INLAND
120H  07/0600Z 31.5N  88.5W   25 KT  30 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER BEVEN
 

WTNT43 KNHC 021500
TCDAT3
 
TROPICAL DEPRESSION THIRTEEN DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL132011
1000 AM CDT FRI SEP 02 2011
 
SATELLITE IMAGERY...SURFACE OBSERVATIONS...AND DOPPLER RADAR DATA 
INDICATE THE CONVECTIVE PATTERN ASSOCIATED WITH TROPICAL DEPRESSION
THIRTEEN HAS IMPROVED DURING THE PAST 6 HOURS...WITH A LARGE AREA
OF VERY COLD CLOUD TOPS OF -80C AND COLDER HAVING DEVELOPED IN THE
EASTERN SEMICIRCLE. HOWEVER...THE RECENT INCREASE IN DEEP
CONVECTION HAS YET TO TRANSLATE INTO AN INCREASE IN THE SURFACE
WINDS. AN AIR FORCE RESERVE RECON AIRCRAFT INVESTIGATING HAS ONLY
MANAGED TO FIND 850 MB FLIGHT-LEVEL OF 37-38 KT. OIL RIG
OBSERVATIONS WELL ABOVE THE SURFACE ALSO SUGGEST THE SYSTEM IS
STILL A DEPRESSION.   
 
THE DEPRESSION HAS BEEN ESSENTIALLY STATIONARY...TRAPPED IN A FLAT
RIDGE PATTERN THAT EXTENDS SOUTHWARD FROM A 700-400 MB HEIGHT
CENTER LOCATED OVER THE OHIO AND TENNESSEE VALLEYS. NARROW RIDGE
AXES EXTEND SOUTHEASTWARD TO FLORIDA AND ALSO SOUTHWESTWARD TO
SOUTH TEXAS...WHICH IS EFFECTIVELY BLOCKING ANY SIGNIFICANT MOTION.
A DEEP TROUGH THAT IS AMPLIFYING OFF THE U.S. EAST COAST IS
EXPECTED TO MAINTAIN THIS BLOCKING PATTERN FOR THE NEXT 36 HOURS OR
SO. BY 48 HOURS...THE BLOCKING PATTERN IS EXPECTED TO SLOWLY BREAK
DOWN AS A WEAK SHORTWAVE TROUGH MOVES EASTWARD ACROSS THE SOUTHERN
AND CENTRAL PLAINS STATES. THIS WEAK PROGRESSIVE PATTERN SHOULD
ALLOW FOR THE CYCLONE TO MOVE SLOWLY TO THE NORTH AND THEN TO THE
NORTHEAST. HOWEVER...THE FORWARD SPEED IS ONLY EXPECTED TO BE
AROUND 5 KT...WHICH IS GOING TO EXACERBATE THE HEAVY RAINFALL
THREAT OVER LOUISIANA AND POINTS NORTHEASTWARD. THE FORECAST TRACK
IS SLIGHTLY EAST OF THE PREVIOUS ADVISORY TRACK...MAINLY DUE TO THE
MORE EASTWARD INITIAL POSITION...AND LIES JUST EAST OF THE NHC
MODEL CONSENSUS.
 
WATER VAPOR IMAGERY AND UPPER-AIR OBSERVATIONS INDICATE A SMALL
UPPER-LEVEL LOW OVER SOUTHWESTERN LOUISIANA THAT HAS BEEN PRODUCING
MODERATE TO STRONG SOUTHWESTERLY WIND SHEAR ACROSS THE CYCLONE HAS
BEEN WEAKENING AND LIFTING OUT TO THE NORTHWEST. THIS HAS ALLOWED
THE WIND SHEAR TO DECREASE AND ALSO TURN TO THE SOUTH AND
SOUTHEAST. DISSIPATION OF THIS UPPER-LEVEL LOW AND ITS ATTENDANT
DRY AIR INFLUENCE IS FORECAST TO OCCUR IN THE NEXT 24
HOURS...ALLOWING THE SYSTEM TO STRENGTHEN.  GIVEN
THE SLOW MOTION...LESSENING SHEAR...AND VERY WARM SSTS NEAR 30C THE
CYCLONE COULD BE NEAR HURRICANE STRENGTH BEFORE LANDFALL OCCURS IN
ABOUT 48 HOURS. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE
NHC INTENSITY CONSENSUS MODEL...ICON...WITH THE STATISTICAL MODELS
ABOVE AND THE DYNAMICAL MODELS BELOW THE OFFICIAL FORECAST.


FORECAST POSITIONS AND MAX WINDS
 
INIT  02/1500Z 27.3N  91.5W   30 KT  35 MPH
 12H  03/0000Z 27.6N  91.5W   35 KT  40 MPH
 24H  03/1200Z 28.2N  91.8W   45 KT  50 MPH
 36H  04/0000Z 28.8N  91.6W   55 KT  65 MPH
 48H  04/1200Z 29.7N  91.3W   55 KT  65 MPH...INLAND
 72H  05/1200Z 29.8N  90.4W   50 KT  60 MPH...INLAND
 96H  06/1200Z 31.0N  88.5W   40 KT  45 MPH...INLAND
120H  07/1200Z 33.0N  87.0W   25 KT  30 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER STEWART
 

