[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 290314
TCDAT2
TROPICAL STORM EARL DISCUSSION NUMBER  15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL072010
1100 PM AST SAT AUG 28 2010

A NOAA HURRICANE HUNTER FLYING A RESEARCH MISSION INTO EARL REPORTED
FLIGHT-LEVEL AND SFMR WINDS SUPPORTING A INITIAL INTENSITY OF 55
KT.  THIS IS IN GOOD AGREEMENT WITH SATELLITE INTENSITY ESTIMATES
FROM TAFB AND SAB OF 55 KT...AND A CIMSS AMSU ESTIMATE OF 56 KT.
THE AIRCRAFT DATA SUGGEST THE CENTRAL PRESSURE IS NEAR 989 MB.
WHILE EARL IS STILL SHOWING SIGNS OF NORTHEASTERLY VERTICAL WIND
SHEAR...THE CONVECTION HAS INCREASED IN BOTH COVERAGE AND
ORGANIZATION DURING THE PAST SEVERAL HOURS.

THE INITIAL MOTION IS 280/17.  EARL IS APPROACHING THE END OF A
LOW/MID-LEVEL RIDGE SEPARATING IT FROM HURRICANE DANIELLE...WITH
WATER VAPOR IMAGERY SHOWING AN UPPER-LEVEL TROUGH JUST NORTH OF
CUBA AND HISPANIOLA.  THE LARGE-SCALE MODELS FORECAST A LOW-LEVEL
RIDGE TO BUILD TO THE NORTH OF EARL DURING THE NEXT 48-72 HR...
WHILE THE TROUGH REMAINS NEARLY STATIONARY AND POSSIBLY
STRENGTHENS.  THE LOW-LEVEL RIDGE WILL STEER EARL GENERALLY TOWARD
THE WEST-NORTHWEST OR WEST WITH SOME DECREASE IN FORWARD
SPEED...WITH THE UPPER TROUGH TRYING TO TURN IT NORTHWARD AS IT
APPROACHES.  OVERALL...THIS PATTERN EVOLUTION SHOULD CAUSE EARL TO
MOVE GENERALLY WEST-NORTHWESTWARD FOR 48 HR OR SO...FOLLOWED BY A
GRADUAL TURN TO THE NORTHWEST AND NORTH AS THE TROUGH EXERTS A
GREATER INFLUENCE.  THE NEW FORECAST TRACK IS SHIFTED A LITTLE
SOUTH OF THE PREVIOUS TRACK DURING THE FIRST 12 HR BASED ON THE
INITIAL POSITION AND MOTION.  AFTER THAT...IT LIES A LITTLE TO LEFT
OF THE CENTER OF THE GUIDANCE ENVELOPE BETWEEN THE CONSENSUS MODELS
AND THE GFDL.  THE NEW TRACK IS SIMILAR TO...BUT A LITTLE SOUTH
OF...THE PREVIOUS TRACK.

THE CURRENT NORTHEASTERLY SHEAR SHOULD GRADUALLY DIMINISH OVER THE
NEXT 24 HR AND ALLOW EARL TO STRENGTHEN.  THE INTENSITY GUIDANCE IS
IN GOOD AGREEMENT THAT EARL SHOULD BECOME A MAJOR HURRICANE BY 72
HR...IF NOT SOONER...AND THIS IS REFLECTED IN THE NHC FORECAST.
THE INTENSITY FORECAST IS MORE PROBLEMATIC AFTER 72 HR...AS THERE
ARE DISAGREEMENTS IN THE LARGE-SCALE MODELS ON HOW MUCH SHEAR EARL
WILL ENCOUNTER AS IT APPROACHES THE UPPER-LEVEL TROUGH.  THE GFS
AND ECMWF FORECAST LIGHT ENOUGH SHEAR TO ALLOW EARL TO MAINTAIN ITS
STRENGTH...WHILE THE UKMET FORECASTS STRONG ENOUGH UPPER-LEVEL
WINDS TO CAUSE EARL TO SHEAR APART.  AT THIS TIME...THE INTENSITY
FORECAST COMPROMISES BETWEEN THESE EXTREMES WITH SLOW WEAKENING
AFTER 96 HR.

THE INITIAL AND FORECAST WIND RADII HAVE BEEN SIGNIFICANTLY REVISED
BASED ON THE AIRCRAFT DATA.

THE NEW FORECAST TRACK REQUIRES HURRICANE WARNINGS TO BE ISSUED FOR
PORTIONS OF THE NORTHERN LEEWARD ISLANDS AT THIS TIME.  ADDITIONAL
WARNINGS WILL BE REQUIRED ON SUNDAY.

FORECAST POSITIONS AND MAX WINDS

INITIAL      29/0300Z 16.6N  55.4W    55 KT
 12HR VT     29/1200Z 17.0N  57.5W    60 KT
 24HR VT     30/0000Z 17.5N  60.0W    70 KT
 36HR VT     30/1200Z 18.1N  62.0W    80 KT
 48HR VT     31/0000Z 19.0N  63.9W    90 KT
 72HR VT     01/0000Z 22.0N  68.0W   100 KT
 96HR VT     02/0000Z 25.0N  71.0W   105 KT
120HR VT     03/0000Z 31.0N  72.5W   100 KT

$$
FORECASTER BEVEN



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