[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 030852
TCDAT5

TROPICAL STORM ERNESTO DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL052012
500 AM AST FRI AUG 03 2012

ERNESTO HAS NOT BECOME ANY BETTER ORGANIZED OVER THE PAST FEW HOURS.
APART FROM A COUPLE OF BRIEF CONVECTIVE BURSTS...CLOUD TOPS HAVE
WARMED AND SHRUNK AROUND THE CENTER OVERNIGHT. IN ADDITION...DATA
FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT SUGGEST THAT
WINDS ARE NOT MIXING DOWN TO THE SURFACE VERY EFFECTIVELY...WHICH
IS CONSISTENT WITH THE LACKLUSTER CONVECTIVE STRUCTURE. THE INITIAL
INTENSITY IS LOWERED TO 40 KT...AND THAT COULD BE SOMEWHAT GENEROUS
GIVEN THAT THE HIGHEST 850-MB WINDS FROM THE AIRCRAFT WERE AROUND
45 KT.

THE RAPID WESTWARD MOTION OF THE LOW-LEVEL CENTER IS RESULTING IN
DEEP-LAYER SHEAR OF AROUND 20 KT AS ANALYZED BY UW-CIMSS AND THE
SHIPS MODEL. GIVEN THIS...AND THE SOMEWHAT DRY AIR SEEN IN UPSTREAM
SOUNDINGS OVER THE LESSER ANTILLES...ONLY MODEST INTENSIFICATION IS
EXPECTED IN THE NEXT DAY OR SO. BEYOND THAT TIME...CONDITIONS
APPEAR TO BECOME MORE FAVORABLE FOR INTENSIFICATION AS THE SHEAR
DECREASES WHILE ERNESTO MOVES OVER WARMER WATERS. HOWEVER...GIVEN
THE CURRENT STRUCTURAL CHALLENGES OF THE CYCLONE AND THE POTENTIAL
FOR LAND INTERACTION...THE OFFICIAL FORECAST WILL REMAIN
CONSERVATIVE. THE NEW NHC FORECAST IS SIMILAR TO THE PREVIOUS
ONE...AND IS BETWEEN THE MORE AGGRESSIVE SHIPS AND LGEM MODELS AND
THE IV15 CONSENSUS THAT INCLUDES THE HFIP GUIDANCE.

THE INITIAL MOTION ESTIMATE IS 275/21...AS ERNESTO IS BEING STEERED
RAPIDLY WESTWARD BY THE STRONG SUBTROPICAL RIDGE TO ITS NORTH. THIS
RIDGE IS FORECAST BY THE GLOBAL MODELS TO BUILD WESTWARD FOR THE
NEXT 2 TO 3 DAYS...WHICH SHOULD RESULT IN A CONTINUED WESTWARD
MOTION OF THE CYCLONE. AFTER 72 HOURS...THE MODELS SHOW A
WEAKNESS DEVELOPING IN THE RIDGE AS A MID-LATITUDE TROUGH MOVES
INTO THE EASTERN UNITED STATES. THIS SHOULD LEAD TO A SLOWER
WEST-NORTHWARD MOTION BY THE END OF THE PERIOD. THERE CONTINUES TO
BE CONSIDERABLE SPREAD IN THE GUIDANCE AT DAYS 3 THROUGH 5...WITH
THE ECMWF SHOWING A WEAKER SYSTEM MOVING WESTWARD AND THE STRONGER
GFDL TURNING ERNESTO MORE TOWARD THE NORTHWEST. DUE TO THE INITIAL
MOTION...THE NEW NHC FORECAST IS A LITTLE FASTER THAN THE PREVIOUS
ADVISORY THROUGH 48 HOURS. AFTER THAT TIME...THE NHC FORECAST IS
LARGELY AN UPDATE OF THE PREVIOUS ONE AND IS CLOSE TO THE MIDDLE OF
THE GUIDANCE ENVELOPE AND THE TVCA/TV15 MULTI-MODEL CONSENSUS.
GIVEN THE LARGE MODEL SPREAD AND THE DEPENDENCE OF THE TRACK ON THE
FUTURE INTENSITY OF THE CYCLONE...CONFIDENCE IN THE TRACK FORECAST
LATE IN THE PERIOD IS LOWER THAN USUAL.


FORECAST POSITIONS AND MAX WINDS

INIT  03/0900Z 13.5N  60.7W   40 KT  45 MPH
 12H  03/1800Z 14.0N  63.5W   45 KT  50 MPH
 24H  04/0600Z 14.4N  66.7W   50 KT  60 MPH
 36H  04/1800Z 14.9N  69.7W   55 KT  65 MPH
 48H  05/0600Z 15.6N  72.8W   60 KT  70 MPH
 72H  06/0600Z 17.0N  78.5W   65 KT  75 MPH
 96H  07/0600Z 18.5N  82.5W   70 KT  80 MPH
120H  08/0600Z 20.5N  86.0W   75 KT  85 MPH

$$
FORECASTER BRENNAN
 
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