000
WTNT44 KNHC 282034
TCDAT4
 
TROPICAL STORM DON DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL042011
400 PM CDT THU JUL 28 2011
 
DON HAS A CLASSIC SHEAR PATTERN IN SATELLITE IMAGERY THIS AFTERNOON
WITH STRONG BURSTS OF CONVECTION OCCURRING NEAR AND SOUTH OF THE
CENTER.  ANALYSES FROM THE SHIPS MODEL AND FROM CIMSS AT THE
UNIVERSITY OF WISCONSIN INDICATE 10-15 KT OF NORTHERLY VERTICAL
WIND SHEAR CONTINUING OVER THE STORM.  IN ADDITION...A STREAM OF
ARC CLOUDS/GUSTS FRONTS ON THE EASTERN SIDE OF THE CIRCULATION
SUGGESTS THAT DRY AIR IS BEING ENTRAINED INTO THE CONVECTION.  DATA
FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT SHOWED THE
CENTRAL PRESSURE RISING TO 1005 MB...WHILE THE AIRCRAFT WINDS
SUPPORTED AN INITIAL INTENSITY OF 40 KT.
 
THE INITIAL MOTION IS NOW 305/14.  DON REMAINS TO THE SOUTH AND
SOUTHWEST OF A DEEP-LAYER RIDGE OVER THE SOUTHEASTERN UNITED
STATES...AND THE LARGE-SCALE MODELS FORECAST THIS FEATURE TO
PERSIST FOR THE NEXT 36-48 HR.  THIS SHOULD STEER DON GENERALLY
NORTHWESTWARD TO WEST-NORTHWESTWARD UNTIL LANDFALL ON THE TEXAS
COAST IN ABOUT 36 HR.  THE TRACK GUIDANCE...WHICH SHIFTED NORTHWARD
BETWEEN 06Z AND 12Z...HAS SHIFTED SOUTHWARD FOR THIS ADVISORY.  THE
NEW FORECAST TRACK HAS BEEN ONLY SLIGHTLY ADJUSTED TO THE SOUTH AND
LIES ON THE RIGHT SIDE OF THE GUIDANCE ENVELOPE.  SOME ADJUSTMENT
TO THE FORECAST TRACK MAY BE NECESSARY IF THE TRACK GUIDANCE
STABILIZES AROUND A TRACK SOUTH OF THE CURRENT FORECAST.
 
THE LARGE-SCALE MODELS AGAIN FORECAST MODERATE SHEAR TO CONTINUE
UNTIL DON MAKES LANDFALL.  THIS AND CONTINUED INTERACTION WITH DRY
AIR OVER THE WESTERN GULF OF MEXICO IS LIKELY TO IMPEDE
INTENSIFICATION...AND THE INTENSITY GUIDANCE IS IN GOOD AGREEMENT
THAT DON WILL MAKE LANDFALL AS A TROPICAL STORM AND NOT AS A
HURRICANE.  THE NEW INTENSITY FORECAST CALLS FOR A LITTLE LESS
STRENGTHENING DURING THE FIRST 12-24 HR DUE TO THE PRESENCE OF
SHEAR AND ARC CLOUDS...THEN CALLS FOR DON TO REACH A PEAK INTENSITY
OF 50 KT NEAR LANDFALL.  AFTER LANDFALL...THE CYCLONE SHOULD WEAKEN
TO A TROPICAL DEPRESSION BY THE 48 HR POINT AND TO A REMNANT LOW BY
THE 72 HR POINT.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  28/2100Z 24.9N  91.3W   40 KT  45 MPH
 12H  29/0600Z 25.8N  93.1W   40 KT  45 MPH
 24H  29/1800Z 26.8N  95.2W   45 KT  50 MPH
 36H  30/0600Z 27.8N  97.5W   50 KT  60 MPH...INLAND
 48H  30/1800Z 28.8N 100.0W   30 KT  35 MPH...INLAND
 72H  31/1800Z 30.5N 103.5W   20 KT  25 MPH...POST-TROP/REMNT LOW
 96H  01/1800Z...DISSIPATED
 
$$
FORECASTER BEVEN