Tropical Storm ERNESTO

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TROPICAL STORM ERNESTO DISCUSSION NUMBER   5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL052006
500 PM EDT FRI AUG 25 2006
 
REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER INDICATE THAT
TROPICAL DEPRESSION FIVE HAS STRENGTHENED INTO TROPICAL STORM
ERNESTO.  THE AIRCRAFT FOUND 48 KT WINDS AT A FLIGHT LEVEL OF 1000
FT ABOUT 40 N MI NORTHEAST OF THE CENTER...ALONG WITH A MINIMUM
CENTRAL PRESSURE OF 1004 MB.  THIS WIND WOULD NORMALLY SUPPORT A 40
KT INTENSITY.  HOWEVER...THE CENTER WAS COMPLETELY EXPOSED AT THAT
TIME...AND THE 48 KT WINDS WERE NOT IN SIGNIFICANT CONVECTION. 
THUS...THE INITIAL INTENSITY IS SET TO A MORE CONSERVATIVE 35 KT IN
AGREEMENT WITH SATELLITE INTENSITY ESTIMATES FROM TAFB AND SAB.

THE EXPOSED CENTER IS TO THE NORTH OF THE PREVIOUS TRACK...AND THE
NEW INITIAL MOTION IS A SOMEWHAT UNCERTAIN 285/14.  OTHERWISE...
THERE IS LITTLE CHANGE IN THE FORECAST PHILOSOPHY OR THE TRACK
FORECAST FOR THE FIRST 72 HR.  ERNESTO IS SOUTH OF A LOW/MID-LEVEL
RIDGE OVER THE WESTERN ATLANTIC...WHICH SHOULD KEEP THE SYSTEM
MOVING GENERALLY WEST-NORTHWESTWARD.  MODEL GUIDANCE SUPPORTS THIS
SCENARIO WITH A TIGHT CLUSTERING OF TRACKS THROUGH THE NORTHWESTERN
CARIBBEAN AND THE WESTERN END OF CUBA...WITH THE EXCEPTION OF THE
GFDL WHICH CONTINUES TO CALL FOR A TRACK OVER THE LENGTH OF CUBA. 
SOME SPREAD APPEARS IN THE GUIDANCE AFTER 72 HR...WITH THE GFS
BUILDING THE RIDGE ACROSS THE GULF OF MEXICO ENOUGH TO TURN ERNESTO
WESTWARD...WHILE THE ECMWF AND CANADIAN MODELS HAVING ENOUGH OF A
WEAKNESS FOR THE CYCLONE TO TURN NORTHWARD.  THE UKMET FORECASTS A
CONTINUED WEST-NORTHWESTWARD MOTION THROUGH 120 HR...WHILE THE
NOGAPS STALLS ERNESTO OVER THE CENTRAL GULF OF MEXICO.  THE NEW
FORECAST TRACK IS NORTH OF...BUT PARALLEL TO...THE PREVIOUS TRACK
FOR THE FIRST 72 HR BASED ON THE NEW POSITION AND MOTION.  IT THEN
CALLS FOR A SLOWER NORTHWESTWARD MOTION OVER THE GULF OF MEXICO IN
RESPONSE TO THE GUIDANCE SPREAD.
 
SATELLITE IMAGERY STILL SHOWS UPPER-LEVEL SOUTHWESTERLY FLOW JUST
NORTHWEST OF ERNESTO.  THIS SUGGESTS THAT THE CURRENT SHEAR WILL
CONTINUE FOR ANOTHER 12 HR OR SO...WITH TRANSIENT BURSTS OF STRONG 
CONVECTION LIKELY.  AFTER THAT...THE LARGE-SCALE MODELS ALL
FORECAST AN UPPER-LEVEL RIDGE OR ANTICYCLONE TO BUILD OVER THE
NORTHWESTERN CARIBBEAN.  WHILE THERE ARE DIFFERENCES IN THE
DETAILS...PARTICULARLY IN THE EXACT POSITION OF THE ANTICYCLONE AND
A SOUTHWARD-MOVING CYCLONIC SHEAR AXIS ON ITS NORTH SIDE...THE
SHEAR IS LIKELY TO DECREASE ENOUGH TO ALLOW ERNESTO TO STRENGTHEN. 
THE INTENSITY FORECAST THUS CALLS FOR SLOW STRENGTHENING FOR THE
FIRST 24-36 HR...WITH SOMEWHAT FASTER STRENGTHENING THEREAFTER. 
THE NEW FORECAST CALLS FOR MORE STRENGTHENING OVER THE GULF OF
MEXICO THAN PREVIOUSLY FORECAST DUE TO THE FORECAST UPPER-LEVEL
WINDS AT 96 AND 120 HR.  ALTHOUGH THE SHIPS AND SUPERENSEMBLE
GUIDANCE CALLS FOR LITTLE CHANGE IN STRENGTH AFTER 96 HR...THERE IS
A CHANCE THAT ERNESTO COULD BE MUCH STRONGER THAN CURRENTLY
FORECAST OVER THE GULF OF MEXICO.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      25/2100Z 14.3N  67.6W    35 KT
 12HR VT     26/0600Z 15.0N  69.7W    35 KT
 24HR VT     26/1800Z 16.0N  72.2W    40 KT
 36HR VT     27/0600Z 17.0N  74.7W    45 KT
 48HR VT     27/1800Z 18.0N  77.2W    55 KT...OVER JAMAICA
 72HR VT     28/1800Z 20.5N  82.0W    65 KT...OVER WATER
 96HR VT     29/1800Z 23.0N  85.5W    70 KT
120HR VT     30/1800Z 24.5N  88.0W    75 KT
 
$$
FORECASTER BEVEN
 
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