000
WTNT42 KNHC 300852
TCDAT2
 
TROPICAL STORM KATIA DISCUSSION NUMBER   5
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122011
500 AM AST TUE AUG 30 2011
 
THE CONVECTIVE PATTERN OF THE CYCLONE HAS IMPROVED OVERNIGHT...WITH
A LARGE AREA OF COLD CLOUD TOPS NOW SITUATED TO THE WEST AND
SOUTHWEST OF THE ESTIMATED CENTER LOCATION. THE 06Z DVORAK
INTENSITY ESTIMATES FROM TAFB AND SAB WERE BOTH 2.5/35 KT...AND ON
THIS BASIS THE CYCLONE IS UPGRADED TO A TROPICAL STORM. THE
STRUCTURE OF KATIA IS CONSISTENT WITH THE 15-20 KT OF
EAST-NORTHEASTERLY SHEAR OVER THE CYCLONE ANALYZED BY THE SHIPS
MODEL AND UW-CIMSS. THIS SHEAR SHOULD DECREASE IN THE NEXT 12 HOURS
OR SO...AND AFTER THAT TIME STEADY INTENSIFICATION SHOULD COMMENCE
AS THE CYCLONE MOVES OVER PROGRESSIVELY HIGHER OCEAN HEAT CONTENT.
MOST OF THE INTENSITY GUIDANCE HAS TRENDED UPWARD THIS CYCLE...AND
THE OFFICIAL FORECAST HAS AS WELL. KATIA IS EXPECTED TO BE NEAR
HURRICANE STRENGTH WITHIN 36 TO 48 HOURS WITH CONTINUED
STRENGTHENING TO NEAR MAJOR HURRICANE STATUS BY THE END OF THE
PERIOD. THE NHC FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS THAT
INCLUDES THE HFIP INTENSITY AIDS.
 
A TIMELY AMSR-E PASS FROM 0326Z WAS HELPFUL IN LOCATING THE CENTER
ON THE EASTERN EDGE OF THE DEEP CONVECTION...WHICH WAS A BIT NORTH
OF PREVIOUS ESTIMATES. THE INITIAL MOTION ESTIMATE IS 290/15...AS
KATIA CONTINUES TO BE STEERED WEST-NORTHWESTWARD BY THE SUBTROPICAL
RIDGE TO ITS NORTH. THE MODEL GUIDANCE IS IN GOOD AGREEMENT ON A
CONTINUATION OF THIS GENERAL MOTION THROUGH THE PERIOD AS THE
MID-LEVEL RIDGE BUILDS WESTWARD TO THE NORTH OF THE CYCLONE. AT
DAYS 4 AND 5...THE WESTERN EDGE OF THE RIDGE BEGINS TO WEAKEN AS A
MID-LEVEL TROUGH AMPLIFIES OVER THE WESTERN ATLANTIC...WHICH SHOULD
RESULT IN SOME DECREASE IN FORWARD SPEED. THE TRACK GUIDANCE
REMAINS TIGHTLY CLUSTERED BUT THERE ARE SOME FORWARD SPEED
DIFFERENCES...WITH THE UKMET AND GFDL MODELS ON THE FAST SIDE OF
THE GUIDANCE AND THE GFS CONTINUING TO BE A SLOW OUTLIER. FOR THIS
CYCLE THE MODELS HAVE TRENDED FASTER DURING THE FIRST 72 HOURS...
AND SO HAS THE OFFICIAL FORECAST. OTHERWISE...THE NHC FORECAST IS
VERY CLOSE TO THE PREVIOUS ONE AND LIES NEAR OR A LITTLE TO THE
RIGHT OF THE TVCA MULTI-MODEL CONSENSUS THROUGH THE PERIOD.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  30/0900Z 11.8N  31.7W   35 KT  40 MPH
 12H  30/1800Z 12.5N  33.7W   40 KT  45 MPH
 24H  31/0600Z 13.5N  36.8W   50 KT  60 MPH
 36H  31/1800Z 14.4N  40.2W   60 KT  70 MPH
 48H  01/0600Z 15.3N  43.7W   70 KT  80 MPH
 72H  02/0600Z 17.0N  49.5W   80 KT  90 MPH
 96H  03/0600Z 18.5N  54.0W   90 KT 105 MPH
120H  04/0600Z 20.5N  58.0W  100 KT 115 MPH
 
$$
FORECASTER BRENNAN