[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 050843
TCDAT5

TROPICAL STORM ERNESTO DISCUSSION NUMBER  15
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL052012
500 AM EDT SUN AUG 05 2012

DATA FROM THE LATEST HURRICANE HUNTER MISSION INTO ERNESTO
SHOWED THAT THE CIRCULATION CONTINUES TO BE RATHER DISORGANIZED.
THE CENTRAL PRESSURE ROSE TO 1009 MB ON THE LAST FIX AND THE
AIRCRAFT FOUND ONLY VERY WEAK WESTERLY WINDS OF LESS THAN 5 KT NEAR
THE CENTER. THE PEAK 850-MB FLIGHT LEVEL WIND WAS 52 KT AND THE
HIGHEST SFMR WINDS WERE 40 TO 45 KT. BASED ON THESE DATA...THE
INITIAL INTENSITY IS SET TO 45 KT. WHILE THE OUTFLOW REMAINS WELL
ESTABLISHED...THE CONVECTIVE STRUCTURE OF THE CYCLONE HAS DEGRADED
OVER THE PAST 6 TO 12 HOURS. RAOB DATA FROM CURACAO...MODEL
ANALYSES AND AIRCRAFT DATA SHOW A TONGUE OF DRY AIR IN THE LOWER TO
MID-TROPOSPHERE IMPINGING ON ERNESTO FROM THE SOUTH. THIS DRY AIR
IN COMBINATION WITH SOME MID-LEVEL SHEAR ANALYZED BY UW-CIMSS MAY
BE PARTLY RESPONSIBLE FOR THE LACK OF DEVELOPMENT IN THE LAST DAY
OR SO. DESPITE OTHERWISE SEEMINGLY FAVORABLE CONDITIONS...THE GFDL
AND HWRF NOW BOTH SHOW THE CYCLONE WEAKENING DURING THE NEXT 48
HOURS. THE SHIPS AND LGEM STILL SHOW INTENSIFICATION...BUT AT A
SLOWER RATE COMPARED TO THEIR PREVIOUS FORECASTS. GIVEN THESE
TRENDS...THE NEW NHC FORECAST HAS BEEN ADJUSTED DOWNWARD THROUGH 48
HOURS...BUT IS STILL ABOVE THE MULTI-MODEL CONSENSUS. AFTER THAT
TIME THERE IS STILL AN OPPORTUNITY FOR ERNESTO TO BECOME A
HURRICANE BEFORE REACHING LAND...WITH SOME RESTRENGTHENING POSSIBLE
AFTER THE CYCLONE MOVES INTO THE GULF OF MEXICO BY DAY 5.

THE LAST FEW AIRCRAFT PASSES THROUGH THE CENTER...SUCH AS IT IS...
SHOWED THAT ERNESTO HAS ACCELERATED BACK TOWARD THE WEST...WITH AN
INITIAL MOTION OF 275/19. THE INITIAL POSITION AND MOTION RESULTS
IN A SHIFT IN THE NHC TRACK OF ABOUT A HALF A DEGREE TO THE LEFT...
OR SOUTH...OF THE PREVIOUS FORECAST. APART FROM THIS ADJUSTMENT...
THERE IS NO CHANGE TO THE OVERALL FORECAST REASONING. ERNESTO IS
EXPECTED TO CONTINUE WESTWARD FOR THE NEXT DAY OR SO AND THEN SLOW
DOWN AND TURN WEST-NORTHWESTWARD BY 48 HOURS AS A WEAKNESS DEVELOPS
IN THE SUBTROPICAL RIDGE OVER THE EASTERN GULF OF MEXICO. THIS
WEST-NORTHWESTWARD MOTION SHOULD CONTINUE THROUGH THE END OF THE
PERIOD AS THE WEAKNESS PERSISTS OVER THE GULF. THE GFS...ECMWF...
AND THE GFS ENSEMBLE MEAN LIE ON THE SOUTHERN SIDE OF THE GUIDANCE
ENVELOPE...SHOWING LESS OF A NORTHWARD TURN AND A TRACK CLOSER TO
THE COAST OF CENTRAL AMERICA AND INTO THE CENTRAL YUCATAN
PENINSULA. THE GFDL...UKMET AND SOME OF THE HFIP MODELS...ARE
FARTHER NORTH AND TAKE THE CYCLONE OVER THE NORTHERN YUCATAN AND
INTO THE CENTRAL GULF. THROUGH 72 HOURS THE NHC FORECAST IS CLOSE
TO THE MIDDLE OF THE GUIDANCE ENVELOPE AND THE MULTI-MODEL
CONSENSUS. AT DAYS 4 AND 5 THE OFFICIAL FORECAST HEDGES TOWARD THE
USUALLY RELIABLE GFS AND ECMWF MODELS AND IS A LITTLE SOUTH OF THE
CONSENSUS.


FORECAST POSITIONS AND MAX WINDS

INIT  05/0900Z 15.1N  74.8W   45 KT  50 MPH
 12H  05/1800Z 15.3N  77.5W   45 KT  50 MPH
 24H  06/0600Z 15.6N  80.1W   50 KT  60 MPH
 36H  06/1800Z 16.0N  82.1W   55 KT  65 MPH
 48H  07/0600Z 16.6N  83.9W   60 KT  70 MPH
 72H  08/0600Z 18.5N  87.5W   75 KT  85 MPH
 96H  09/0600Z 20.5N  91.0W   60 KT  70 MPH
120H  10/0600Z 21.6N  94.0W   65 KT  75 MPH

$$
FORECASTER BRENNAN



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