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Tropical Storm MATTHEW (Text)

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TROPICAL STORM MATTHEW DISCUSSION NUMBER   4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL152010
500 AM EDT FRI SEP 24 2010
 
MATTHEW HAS GOTTEN SLIGHTLY BETTER ORGANIZED OVER THE PAST SEVERAL
HOURS.  WHILE THE STORM HAS A LARGE CONVECTIVE CLUSTER WITH CLOUD
TOPS COLDER THAN -80C...THE LOW-LEVEL CENTER IS NEAR THE EASTERN
EDGE OF THE CONVECTION.  THIS IS LIKELY DUE TO 15 KT OF EAST-
NORTHEASTERLY VERTICAL WIND SHEAR SHOWN IN ANALYSES FROM CIMSS AT
THE UNIVERSITY OF WISCONSIN.  IN ADDITION...EARLIER MICROWAVE DATA
SUGGESTS THAT THERE ARE MULTIPLE LOW-LEVEL SWIRLS PRESENT. 
SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM TAFB AND 35 KT FROM
SAB...AND BASED ON THESE THE INITIAL INTENSITY IS INCREASED TO 45
KT.
 
THE INITIAL MOTION IS 275/14.  MATTHEW IS ON THE SOUTH SIDE OF THE
SUBTROPICAL RIDGE...WHICH IS EXPECTED TO STEER THE CYCLONE WESTWARD
TO WEST-NORTHWESTWARD WITH SOME DECREASE IN FORWARD SPEED FOR THE
NEXT 36-48 HR.  THE GUIDANCE IS IN GOOD AGREEMENT WITH THIS...AND
THE NEW FORECAST TRACK LIES A LITTLE TO THE NORTH OF THE CENTER OF
THE GUIDANCE ENVELOPE.  AFTER THAT TIME...THERE IS SERIOUS
DIVERGENCE IN THE GUIDANCE.  THE OPERATIONAL GLOBAL MODELS AGREE
THAT MATTHEW SHOULD CONTINUE WEST-NORTHWESTWARD ACROSS THE SOUTHERN
YUCATAN PENINSULA AND/OR GUATEMALA...WITH THE UKMET SHOWING THE
CENTER REACHING THE BAY OF CAMPECHE.  ON THE OTHER HAND...THE
GFDL..HWRF...AND GFS ENSEMBLE MEAN FORECAST MATTHEW TO REACH THE
EAST COAST OF YUCATAN AND THEN TURN NORTHEASTWARD.  THE DIFFERENCES
APPEAR TO STEM FROM THE INTERACTION OF MATTHEW WITH A DEVELOPING
MONSOON LOW PRESSURE AREA OVER CENTRAL AMERICA AND THE ADJACENT
WATERS...AND TO A LESSER EXTENT ON THE DEVELOPMENT OF A DEEP-LAYER
TROUGH OVER THE CENTRAL AND EASTERN UNITED STATES.  FOR NOW...THE
TRACK FORECAST WILL COMPROMISE BETWEEN THESE EXTREMES AND CALL FOR
A SLOW NORTHWARD MOTION OVER THE YUCATAN PENINSULA TO KEEP
CONTINUITY FROM THE PREVIOUS FORECAST.  HOWEVER...THIS IS A
LOW-CONFIDENCE FORECAST...AND SIGNIFICANT CHANGES MAY BE REQUIRED
LATER TODAY.
 
THE CURRENT SHEAR IS FORECAST TO SUBSIDE IN 12-24 HR...SO THE MAIN
FACTOR CONTROLLING THE INTENSITY WILL BE LAND INTERACTION.  THE NEW
FORECAST TRACK HAS MATTHEW PASSING OVER MORE LAND THAN PREVIOUSLY
AND THE FORECAST INTENSITIES HAVE THUS BEEN LOWERED.  IT SHOULD BE
NOTED THAT NONE OF THE INTENSITY GUIDANCE SHOWS MATTHEW BECOMING A
HURRICANE BEFORE REACHING HONDURAS AND NICARAGUA...BUT THIS
POSSIBILITY CANNOT BE RULED OUT.  THE INTENSITY OF MATTHEW AFTER 48
HR IS HIGHLY DEPENDENT ON WHICH GROUPS OF MODELS ARE CORRECT ABOUT
THE TRACK.  IF THE GLOBAL MODELS VERIFY...THE CYCLONE WILL LIKELY
DISSIPATE OVER EASTERN MEXICO OR GUATEMALA.  IF THE GFDL/HWRF
VERIFY...THE SYSTEM WILL BE STRONGER THAN FORECAST OVER THE
CARIBBEAN WATERS.  THE LATTER PART OF THE INTENSITY FORECAST IS A
COMPROMISE BETWEEN THESE EXTREMES...AND LIKE THE TRACK FORECAST...IT
IS OF LOW CONFIDENCE.
 
 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      24/0900Z 14.3N  79.8W    45 KT
 12HR VT     24/1800Z 14.8N  82.0W    50 KT
 24HR VT     25/0600Z 15.5N  84.5W    50 KT...INLAND
 36HR VT     25/1800Z 16.2N  86.5W    50 KT...OVER WATER
 48HR VT     26/0600Z 16.7N  87.9W    60 KT
 72HR VT     27/0600Z 17.5N  89.5W    35 KT...INLAND
 96HR VT     28/0600Z 18.5N  89.5W    30 KT...INLAND
120HR VT     29/0600Z 19.5N  89.5W    25 KT...INLAND
 
$$
FORECASTER BEVEN
 
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