WTNT42 KNHC 172125
TCDAT2
 
TROPICAL STORM HELENE SPECIAL DISCUSSION NUMBER   9
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072012
430 PM CDT FRI AUG 17 2012
 
THE AIR FORCE HURRICANE HUNTER AIRCRAFT INVESTIGATING THE REMNANTS
OF TROPICAL DEPRESSION SEVEN FOUND A WELL-DEFINED CIRCULATION AND
PEAK FLIGHT LEVEL WINDS OF ABOUT 50 KT AND BIAS-CORRECTED SFMR
WINDS OF 38 KT. BASED ON THESE DATA...THE SYSTEM IS NOW UPGRADED TO
TROPICAL STORM HELENE WITH AN INTENSITY OF 40 KT...ALTHOUGH THESE
WINDS COULD BE ENHANCED SOMEWHAT BY TOPOGRAPHY AND DECAYING
CONVECTION NEAR THE CENTER. THE SATELLITE PRESENTATION OF THE
CYCLONE IS SOMEWHAT LACKLUSTER...WITH MOST OF THE DEEP CONVECTION
DISPLACED WEST OF THE CENTER LOCATION. THAT BEING SAID...THERE IS
SOME POTENTIAL FOR SLIGHT INTENSIFICATION BEFORE THE CYCLONE MOVES
INLAND WITHIN 24 HOURS. AFTER LANDFALL...STEADY DECAY IS EXPECTED
TO REMNANT LOW STATUS BY 48 HOURS WITH DISSIPATION EXPECTED BY 72
HOURS.
 
THE INITIAL MOTION ESTIMATE IS A SOMEWHAT UNCERTAIN 310/06. HELENE
IS EXPECTED TO MOVE NORTHWESTWARD AND INLAND OVER THE GULF COAST OF
MEXICO IN THE NEXT DAY OR SO AS THE MID-LEVEL RIDGE OVER NORTHERN
MEXICO AND THE SOUTHWESTERN U.S. RETREATS NORTHWARD. THE NHC
FORECAST IS A LITTLE TO THE LEFT OF THE TVCA CONSENSUS AND TO THE
RIGHT OF THE ECMWF THROUGH DISSIPATION.
 
THE MAIN THREAT FROM HELENE WILL BE HEAVY RAINFALL...WHICH WILL
CONTINUE EVEN AS THE CYCLONE MOVES INLAND AND WEAKENS.
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  17/2130Z 20.6N  96.1W   40 KT  45 MPH
 12H  18/0600Z 21.1N  96.9W   45 KT  50 MPH
 24H  18/1800Z 22.1N  98.1W   35 KT  40 MPH...INLAND
 36H  19/0600Z 22.9N  99.0W   30 KT  35 MPH...INLAND
 48H  19/1800Z 23.5N  99.5W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  20/1800Z...DISSIPATED
 
$$
FORECASTER BRENNAN
 

WTNT42 KNHC 180232
TCDAT2
 
TROPICAL STORM HELENE DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072012
1000 PM CDT FRI AUG 17 2012

A HURRICANE HUNTER PLANE INVESTIGATED HELENE FOR SEVERAL HOURS THIS
EVENING AND FOUND THAT THE DEVELOPMENT TREND OBSERVED EARLIER TODAY
IS NO LONGER OCCURRING. HELENE IS EITHER WEAKER OR ON A STEADY
STATE WITH MAXIMUM WINDS OF 35 KNOTS. THE CYCLONE STILL HAS A WELL
DEFINED CIRCULATION AS INDICATED BY THE RECONNAISSANCE PLANE BEFORE
IT LEFT THE AREA...AND ALTHOUGH THE SATELLITE PRESENTATION HAS
DETERIORATED...ENVIRONMENTAL CONDITIONS ARE SOMEWHAT FAVORABLE FOR
HELENE TO REGAIN SOME STRENGTH BEFORE IT MOVES INLAND IN ABOUT 24
HOURS OR EARLIER. AFTER LANDFALL...A STEADY WEAKENING IS
ANTICIPATED.

FIXES FROM THE RECONNAISSANCE PLANE INDICATE THAT HELENE WAS
MEANDERING OR DRIFTING NORTHWARD DURING THE PAST COUPLE OF HOURS.
HOWEVER...THERE IS ENOUGH RIDGING TO THE NORTH OF THE CYCLONE TO
FORCE HELENE SLOWLY NORTHWESTWARD AT ABOUT 6 KNOTS TOWARD THE COAST
OF MEXICO. ALTHOUGH THIS IS THE MOST LIKELY SCENARIO AS INDICATED IN
THE OFFICIAL FORECAST...ONE SHOULD NOTE THAT VARIOUS MODELS
INCLUDING THE GFS AND THE ECMWF KEEP A LOW...OR PERHAPS THE MODEL
REPRESENTATION OF HELENE DRIFTING NORTHWARD VERY CLOSE TO THE COAST
OF MEXICO FOR SEVERAL DAYS...AND IN FACT...THE GFS RESTRENGTHENS
THIS FEATURE.      
 
NEVERTHELESS...THE MAIN THREAT FROM HELENE WILL BE HEAVY
RAINFALL...WHICH WILL CONTINUE EVEN AS THE CYCLONE SLOWLY MOVES
INLAND AND WEAKENS.
  
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/0300Z 21.0N  96.4W   35 KT  40 MPH
 12H  18/1200Z 21.7N  97.2W   40 KT  45 MPH
 24H  19/0000Z 22.2N  97.8W   45 KT  50 MPH...ON THE COAST
 36H  19/1200Z 23.0N  98.0W   30 KT  35 MPH...INLAND
 48H  20/0000Z 24.0N  98.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  21/0000Z...DISSIPATED
 
$$
FORECASTER AVILA
 

WTNT42 KNHC 180908
TCDAT2
 
TROPICAL STORM HELENE DISCUSSION NUMBER  11
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072012
400 AM CDT SAT AUG 18 2012
 
DEEP CONVECTION ASSOCIATED WITH HELENE HAS BEEN MINIMAL DURING THE
LAST SEVERAL HOURS. THE INITIAL WIND SPEED IS HELD AT 35 KT FOR
NOW...BUT IT IS POSSIBLE THAT HELENE IS A LITTLE WEAKER THAN THAT.
SINCE THE CYCLONE ONLY HAS A SHORT TIME BEFORE IT BEGINS
INTERACTING WITH LAND...STRENGTHENING IS NO LONGER ANTICIPATED.
THE NEW OFFICIAL FORECAST IS LOWERED FROM THE PREVIOUS ONE AND
SHOWS LITTLE CHANGE IN STRENGTH BEFORE LANDFALL. AFTER THE CENTER
MOVES INLAND...STEADY WEAKENING AND DEGENERATION TO A REMNANT LOW
ARE ANTICIPATED.
 
A SERIES OF MICROWAVE IMAGES AND RADAR IMAGERY FROM MEXICO INDICATE
THAT THE CENTER OF HELENE HAS BEEN WOBBLING AROUND. SMOOTHING
THROUGH THE WOBBLES YIELDS AN INITIAL MOTION ESTIMATE OF 315/6. A
MID-LEVEL RIDGE LOCATED OVER NORTHERN MEXICO APPEARS TO BE STRONG
ENOUGH TO STEER HELENE NORTHWESTWARD FOR ANOTHER 12 TO 24 HOURS.
THIS TRACK SHOULD TAKE HELENE INLAND OVER THE GULF COAST OF MEXICO
LATER TODAY. AFTER LANDFALL...THE WEAKENING SYSTEM IS EXPECTED TO
SLOW DOWN AND TURN TO THE NORTH ALONG THE COAST OF MEXICO UNTIL IT
DISSIPATES.
  
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/0900Z 21.6N  97.0W   35 KT  40 MPH
 12H  18/1800Z 21.9N  97.6W   35 KT  40 MPH...NEAR THE COAST
 24H  19/0600Z 22.4N  98.1W   35 KT  40 MPH...INLAND
 36H  19/1800Z 23.1N  97.9W   25 KT  30 MPH...POST-TROP/REMNT LOW
 48H  20/0600Z 23.8N  97.8W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  21/0600Z...DISSIPATED
 
$$
FORECASTER CANGIALOSI/BEVEN
 

WTNT42 KNHC 181433
TCDAT2
 
TROPICAL DEPRESSION HELENE DISCUSSION NUMBER  12
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072012
1000 AM CDT SAT AUG 18 2012
 
SATELLITE DATA...SURFACE OBSERVATIONS...AND MEXICAN RADAR DATA FROM
ALTAMIRA INDICATE THAT THE CENTER OF HELENE IS LOCATED JUST INLAND
FROM THE COAST VERY NEAR TAMPICO MEXICO.  A NEW BURST OF DEEP
CONVECTION APPEARS TO BE DEVELOPING NEAR THE CENTER...BUT THE
DEEPEST CONVECTION LIES IN BANDS TO THE EAST OVER THE WATER. 
DVORAK FINAL-T ESTIMATES FROM TAFB AND SAB...AND SCATTEROMETER
DATA...NO LONGER SUPPORT TROPICAL STORM STATUS...AND HELENE IS
DOWNGRADED TO A TROPICAL DEPRESSION AT THIS TIME.  WEAKENING SHOULD
CONTINUE AS THE DEPRESSION MOVES OVER LAND...AND HELENE COULD
BECOME A REMNANT LOW BY TONIGHT.  ALTHOUGH THE GFS MODEL SHOWS
HELENE RE-STRENGTHENING OVER WATER IN 2-3 DAYS...THE OFFICIAL
FORECAST FOLLOWS THE OTHER MODELS AND INDICATES DISSIPATION BY 48
HOURS.
 
AFTER MOVING VERY LITTLE LAST EVENING...HELENE APPEARS TO HAVE
ACCELERATED OVERNIGHT AND HAS AN ESTIMATED MOTION OF 305/8 KT.  THE
CYCLONE SHOULD TURN NORTHWARD AND SLOW DOWN DURING THE NEXT DAY OR
SO SINCE IT WILL BE STEERED AROUND THE WESTERN PERIPHERY OF A
LOW/MID-LEVEL RIDGE...AND TRAPPED AGAINST THE EASTERN SLOPES OF THE
SIERRA MADRE OCCIDENTALS.  THE UPDATED NHC TRACK FORECAST IS JUST A
LITTLE SLOWER THAN THE PREVIOUS ONE. 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/1500Z 22.0N  98.0W   30 KT  35 MPH...INLAND
 12H  19/0000Z 22.6N  98.7W   25 KT  30 MPH...INLAND
 24H  19/1200Z 23.0N  98.8W   25 KT  30 MPH...POST-TROP/REMNT LOW
 36H  20/0000Z 23.5N  98.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 48H  20/1200Z...DISSIPATED
 
$$
FORECASTER BERG
 

WTNT42 KNHC 182032
TCDAT2
 
TROPICAL DEPRESSION HELENE DISCUSSION NUMBER  13
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL072012
400 PM CDT SAT AUG 18 2012
 
HELENE IS MOVING FARTHER INLAND OVER NORTHEASTERN MEXICO...AND IT
CONTINUES TO PRODUCE DEEP CONVECTION MAINLY DUE TO UPSLOPE FLOW ON
THE EASTERN SLOPES OF THE SIERRA MADRE.  THE INTENSITY IS LOWERED TO
25 KT BASED ON A 1554 UTC ASCAT PASS...WHICH BARELY SHOWED 20-25 KT
OF WIND OVER THE WESTERN GULF OF MEXICO.  THE CIRCULATION APPEARS
TO BE LOSING SOME DEFINITION...AND DISSIPATION SHOULD OCCUR SOON IF
THE GLOBAL MODELS ARE RIGHT.  THE OFFICIAL FORECAST SHOWS HELENE
BECOMING A REMNANT LOW AND DISSIPATING DURING THE NEXT 24 HOURS.

HELENE HAS SLOWED DOWN NOW THAT IT IS OVER LAND...AND THE ESTIMATED
MOTION IS 295/4 KT.  THE CYCLONE IS LIKELY TO RUN INTO THE EASTERN
EDGE OF THE HIGHER TERRAIN SOON...AND IT IS FORECAST TO TURN
NORTHWESTWARD BEFORE DISSIPATION.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/2100Z 22.6N  98.8W   25 KT  30 MPH...INLAND
 12H  19/0600Z 22.9N  99.2W   20 KT  25 MPH...POST-TROP/REMNT LOW
 24H  19/1800Z...DISSIPATED
 
$$
FORECASTER BERG
 

