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 715 
 WTNT45 KNHC 240851
 TCDAT5
 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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