HOME	ACTIVE CYCLONES	FORECASTS	IMAGERY	ABOUT TPC	RECONNAISSANCE

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TROPICAL STORM IRENE DISCUSSION NUMBER   3
NATIONAL WEATHER SERVICE MIAMI FL
11 PM EDT WED OCT 13 1999

AIR FORCE RECON FOUND 56 KNOTS OVER THE NORTHWEST QUADRANT SEVERAL
HOURS AGO.  THE PRESENTATION ON SATELLITE IMAGERY CONTINUES TO LOOK
MORE IMPRESSIVE.  LATEST SATELLITE-DERIVED INTENSITY ESTIMATES ARE
3.5 ON THE DVORAK SCALE...I.E. 55 KNOTS.  THERE IS EXCELLENT UPPER-
LEVEL OUTFLOW OVER THE STORM AND THE WATERS ARE QUITE WARM.  IRENE
IS LIKELY TO INTENSIFY INTO A HURRICANE IN 12 HOURS...ABOUT THE TIME
IT REACHES WESTERN CUBA.  ADDITIONAL STRENGTHENING IS PREDICTED OVER
THE SOUTHEASTERN GULF OF MEXICO.  HOWEVER INCREASING UPPER-LEVEL
SOUTHWESTERLY WINDS MAY LIMIT INTENSIFICATION LATER IN THE FORECAST
PERIOD.

A WELL-DEFINED MID- TO UPPER-TROPOSPHERIC TROUGH IN THE WESTERLIES
IS APPROACHING THE U.S. EAST COAST...AND CURRENTLY PASSING THE
LONGITUDE OF IRENE.  AS THIS FEATURE BYPASSES THE TROPICAL CYCLONE
AND MOVES ON OUT INTO THE ATLANTIC...THE STEERING CURRENT NEAR IRENE
SHOULD WEAKEN.  HENCE THE OFFICIAL FORECAST SLOWS THE FORWARD SPEED
DURING THE NEXT DAY OR SO.  NEAR THE END OF THE FORECAST PERIOD...A
NEW MIDLATITUDE TROUGH...WHICH IS CURRENTLY OVER NORTHWESTERN NORTH
AMERICA...IS EXPECTED TO DROP INTO THE MIDWEST.  THIS SHOULD PRODUCE
A SOUTH-SOUTHWESTERLY STEERING FLOW FOR IRENE.  HOWEVER THERE IS
SIGNIFICANT UNCERTAINTY IN THE FORECAST LATER IN THE PERIOD AS
REFLECTED BY THE SPREAD OF THE TRACK GUIDANCE MODELS.  FOR EXAMPLE
THE U.K. MET. OFFICE MODEL KEEPS IRENE OVER THE EASTERN GULF THROUGH
72 HOURS BUT THE NAVY VERSION OF THE GFDL MODEL ACCELERATES THE
CYCLONE INTO EASTERN GEORGIA BY THAT TIME.  THE OFFICIAL FORECAST IS
A REASONABLE BLEND OF THE GUIDANCE...AND IS QUITE SIMILAR TO THAT
FROM THE PREVIOUS ADVISORY.
 
ALL INTERESTS IN FLORIDA SHOULD CLOSELY MONITOR THE PROGRESS OF
THIS STRENGTHENING STORM.  ADDITIONAL WATCHES...OR PERHAPS
WARNINGS...MAY BE REQUIRED FOR SOME PORTION OF FLORIDA ON THURSDAY.
 
PASCH
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL     14/0300Z 21.1N  83.5W    55 KTS
12HR VT     14/1200Z 22.3N  83.5W    65 KTS
24HR VT     15/0000Z 23.3N  83.5W    70 KTS
36HR VT     15/1200Z 24.5N  83.4W    75 KTS
48HR VT     16/0000Z 26.0N  83.0W    80 KTS
72HR VT     17/0000Z 28.0N  82.5W    80 KTS
 
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