000
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