Issued at 1100 PM AST THU JUL 25 2013
000
WTNT44 KNHC 260241
TCDAT4
TROPICAL STORM DORIAN DISCUSSION NUMBER 8
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042013
1100 PM AST THU JUL 25 2013
THE CONVECTIVE STRUCTURE OF DORIAN HAS NOT BEEN PARTICULARLY
ORGANIZED THIS EVENING...AND RECENT MICROWAVE IMAGERY INDICATES
THAT THE LOW-LEVEL CENTER LIES TO THE SOUTHWEST OF THE DEEP
CONVECTION. A 2340 UTC ASCAT-B OVERPASS INDICATES THAT DORIAN HAS
WEAKENED A BIT...AND THE INITIAL INTENSITY IS NOW 45 KT.
DORIAN IS BEING DRIVEN QUICKLY WEST-NORTHWESTWARD BY A LOW- TO
MID-LEVEL ANTICYCLONE OVER THE CENTRAL ATLANTIC...AND ITS ESTIMATED
MOTION IS 285/17 KT. THE ANTICYCLONE IS FORECAST TO MOVE WESTWARD
IN TANDEM WITH DORIAN THROUGH DAY 3...BUT THE GLOBAL MODELS THEN
SUGGEST THAT THIS FEATURE WILL EVOLVE INTO A NORTHEAST-TO-SOUTHWEST
ORIENTED RIDGE AXIS THAT EXTENDS ACROSS FLORIDA BY DAYS 4 AND 5.
BECAUSE OF THIS PATTERN EVOLUTION...THE TRACK GUIDANCE ENVELOPE HAS
SHIFTED A LITTLE SOUTHWARD ON THIS CYCLE. THE 18Z RUN OF THE GFS
IS VERY SIMILAR TO THE 12Z RUN AND IS THE SOUTHERNMOST AND SLOWEST
TRACK MODEL WHILE THE ECMWF IS THE NORTHERNMOST AND FASTEST. THE
NHC TRACK FORECAST HAS BEEN NUDGED A BIT SOUTH OF THE PREVIOUS
FORECAST TO FOLLOW THE OVERALL TREND IN THE GUIDANCE...BUT IT ENDS
UP CLOSE TO THE ECMWF TRACK ON THE NORTHERN SIDE OF THE ENVELOPE.
DORIAN IS EMBEDDED IN AN ENVIRONMENT OF FAST EASTERLY LOW-LEVEL FLOW
AND RELATIVELY LIGHT UPPER-LEVEL WINDS...WHICH APPEARS TO BE
INDUCING SOME WESTERLY TO SOUTHWESTERLY SHEAR IN THE LAYER BELOW
THE CIRRUS OUTFLOW. SINCE THE FORWARD SPEED OF THE CYCLONE IS NOT
EXPECTED TO SLOW DOWN ANY TIME SOON...DORIAN COULD EXPERIENCE
PERSISTENT SHEAR FOR THE NEXT FEW DAYS. ON TOP OF THAT...MID-LEVEL
RELATIVE HUMIDITIES ARE EXPECTED TO DECREASE...AND THE DRY AIR
COULD INHIBIT DEEP CONVECTION. NONE OF THE GUIDANCE SHOWS MUCH
CHANGE IN INTENSITY DURING THE NEXT FEW DAYS...SO THE OFFICIAL
FORECAST WILL KEEP THE WINDS FLATLINED AT 45 KT THROUGH DAY 3 WITH
NOT MUCH STRENGTHENING THEREAFTER. THIS FORECAST IS A BIT LOWER
THAN THE PREVIOUS ONE...PARTIALLY TO ACCOUNT FOR THE LOWER INITIAL
INTENSITY.
FORECAST POSITIONS AND MAX WINDS
INIT 26/0300Z 16.6N 39.6W 45 KT 50 MPH
12H 26/1200Z 17.2N 42.4W 45 KT 50 MPH
24H 27/0000Z 17.8N 46.4W 45 KT 50 MPH
36H 27/1200Z 18.3N 50.4W 45 KT 50 MPH
48H 28/0000Z 19.0N 54.3W 45 KT 50 MPH
72H 29/0000Z 20.0N 61.5W 45 KT 50 MPH
96H 30/0000Z 20.5N 67.5W 50 KT 60 MPH
120H 31/0000Z 21.0N 72.0W 50 KT 60 MPH
$$
FORECASTER BERG
Continue reading...
000
WTNT44 KNHC 260241
TCDAT4
TROPICAL STORM DORIAN DISCUSSION NUMBER 8
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042013
1100 PM AST THU JUL 25 2013
THE CONVECTIVE STRUCTURE OF DORIAN HAS NOT BEEN PARTICULARLY
ORGANIZED THIS EVENING...AND RECENT MICROWAVE IMAGERY INDICATES
THAT THE LOW-LEVEL CENTER LIES TO THE SOUTHWEST OF THE DEEP
CONVECTION. A 2340 UTC ASCAT-B OVERPASS INDICATES THAT DORIAN HAS
WEAKENED A BIT...AND THE INITIAL INTENSITY IS NOW 45 KT.
DORIAN IS BEING DRIVEN QUICKLY WEST-NORTHWESTWARD BY A LOW- TO
MID-LEVEL ANTICYCLONE OVER THE CENTRAL ATLANTIC...AND ITS ESTIMATED
MOTION IS 285/17 KT. THE ANTICYCLONE IS FORECAST TO MOVE WESTWARD
IN TANDEM WITH DORIAN THROUGH DAY 3...BUT THE GLOBAL MODELS THEN
SUGGEST THAT THIS FEATURE WILL EVOLVE INTO A NORTHEAST-TO-SOUTHWEST
ORIENTED RIDGE AXIS THAT EXTENDS ACROSS FLORIDA BY DAYS 4 AND 5.
BECAUSE OF THIS PATTERN EVOLUTION...THE TRACK GUIDANCE ENVELOPE HAS
SHIFTED A LITTLE SOUTHWARD ON THIS CYCLE. THE 18Z RUN OF THE GFS
IS VERY SIMILAR TO THE 12Z RUN AND IS THE SOUTHERNMOST AND SLOWEST
TRACK MODEL WHILE THE ECMWF IS THE NORTHERNMOST AND FASTEST. THE
NHC TRACK FORECAST HAS BEEN NUDGED A BIT SOUTH OF THE PREVIOUS
FORECAST TO FOLLOW THE OVERALL TREND IN THE GUIDANCE...BUT IT ENDS
UP CLOSE TO THE ECMWF TRACK ON THE NORTHERN SIDE OF THE ENVELOPE.
DORIAN IS EMBEDDED IN AN ENVIRONMENT OF FAST EASTERLY LOW-LEVEL FLOW
AND RELATIVELY LIGHT UPPER-LEVEL WINDS...WHICH APPEARS TO BE
INDUCING SOME WESTERLY TO SOUTHWESTERLY SHEAR IN THE LAYER BELOW
THE CIRRUS OUTFLOW. SINCE THE FORWARD SPEED OF THE CYCLONE IS NOT
EXPECTED TO SLOW DOWN ANY TIME SOON...DORIAN COULD EXPERIENCE
PERSISTENT SHEAR FOR THE NEXT FEW DAYS. ON TOP OF THAT...MID-LEVEL
RELATIVE HUMIDITIES ARE EXPECTED TO DECREASE...AND THE DRY AIR
COULD INHIBIT DEEP CONVECTION. NONE OF THE GUIDANCE SHOWS MUCH
CHANGE IN INTENSITY DURING THE NEXT FEW DAYS...SO THE OFFICIAL
FORECAST WILL KEEP THE WINDS FLATLINED AT 45 KT THROUGH DAY 3 WITH
NOT MUCH STRENGTHENING THEREAFTER. THIS FORECAST IS A BIT LOWER
THAN THE PREVIOUS ONE...PARTIALLY TO ACCOUNT FOR THE LOWER INITIAL
INTENSITY.
FORECAST POSITIONS AND MAX WINDS
INIT 26/0300Z 16.6N 39.6W 45 KT 50 MPH
12H 26/1200Z 17.2N 42.4W 45 KT 50 MPH
24H 27/0000Z 17.8N 46.4W 45 KT 50 MPH
36H 27/1200Z 18.3N 50.4W 45 KT 50 MPH
48H 28/0000Z 19.0N 54.3W 45 KT 50 MPH
72H 29/0000Z 20.0N 61.5W 45 KT 50 MPH
96H 30/0000Z 20.5N 67.5W 50 KT 60 MPH
120H 31/0000Z 21.0N 72.0W 50 KT 60 MPH
$$
FORECASTER BERG
Continue reading...