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Tropical Depression IGOR


ZCZC MIATCDAT1 ALL
TTAA00 KNHC DDHHMM
TROPICAL DEPRESSION IGOR DISCUSSION NUMBER   7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL112010
1100 PM AST THU SEP 09 2010
 
INFRARED SATELLITE IMAGES INDICATE A BURST OF DEEP CONVECTION OVER
THE WESTERN SEMICIRCLE OF IGOR DURING THE LAST SEVERAL HOURS...WITH
CLOUD TOP TEMPERATURES AS COLD AS -90 C. THIS BURSTING PATTERN
SUGGESTS THAT EASTERLY VERTICAL WIND SHEAR CONTINUES OVER
THE CYCLONE...AND THIS IS CONFIRMED BY UW-CIMSS SHEAR ANALYSES
SHOWING ABOUT 20 KT OF EASTERLY SHEAR.  DVORAK INTENSITY ESTIMATES
ARE AT 2.5/35 KT FROM TAFB...AND 3-HOURLY AVERAGED ADT VALUES ARE
CLOSE TO THIS VALUE. A STRICT INTERPRETATION OF THE SATELLITE
ESTIMATES SUGGEST THAT IGOR MAY BE NEARING TROPICAL STORM STRENGTH
AGAIN.  HOWEVER...GIVEN THE LACK OF PERSISTENCE OF THE CURRENT
BURST OF CONVECTION...THE INITIAL INTENSITY IS HELD AT 30 KT FOR
THIS ADVISORY.
 
A REFORMATION OF THE LOW-LEVEL CENTER DURING THE LAST 12 HOURS HAS
MADE DISCERNING AN INITIAL MOTION ESTIMATE MORE DIFFICULT THAN
NORMAL.  GIVEN THE DISCONTINUITY IN CENTER FIXES...A LONGER-TERM
MOTION WAS COMPUTED AND YIELDS AN UNCERTAIN 295/11. GLOBAL
DYNAMICAL MODELS ARE GENERALLY IN GOOD AGREEMENT THAT IGOR WILL BE
STEERED ON A MORE WESTWARD TRACK AT A FASTER FORWARD SPEED BY THE
FLOW ON THE SOUTH SIDE OF A SUBTROPICAL RIDGE THROUGH ABOUT 72
HOURS.  THEREAFTER...IGOR IS EXPECTED TO TURN MORE WEST-
NORTHWESTWARD AND SLOW LATE IN THE FORECAST PERIOD AS IT APPROACHES
A WEAKNESS IN THE SUBTROPICAL RIDGE OVER THE CENTRAL ATLANTIC.
THE SPREAD IN THE MODEL GUIDANCE HAS INCREASED THIS CYCLE IN
RESPONSE TO THE DIFFERENCES IN THE WAY MODELS HANDLE THE EVOLUTION
OF THIS WEAKNESS.  THE REFORMATION OF THE CENTER AND A NOTABLE
SOUTHWARD AND WESTWARD SHIFT TO THE GUIDANCE HAS PROMPTED A FAIRLY
SIGNIFICANT THE OFFICIAL NHC TRACK FORECAST IN THAT DIRECTION...
THOUGH THE TRACK FORECAST REMAINS ON THE NORTHERN SIDE OF THE
GUIDANCE ENVELOPE.
 
A CONTINUATION OF MODERATE EASTERLY SHEAR SHOULD SLOW OR POSSIBLY
EVEN HALT FURTHER INTENSIFICATION FOR AT LEAST THE NEXT 24 HOURS.
SHIPS MODEL OUTPUT INDICATES A REDUCTION IN THE SHEAR...A FAIRLY
MOIST ATMOSPHERE...AND RELATIVELY WARM SEA SURFACE TEMPERATURES
AHEAD OF IGOR FROM 24-72 HOURS.  THESE INGREDIENTS SHOULD FAVOR A
STEADIER RATE OF INTENSIFICATION DURING THAT TIME.  THEREAFTER...THE
INTENSITY FORECAST BECOMES A BIT TRICKIER. THE STATISTICAL GUIDANCE
INDICATES POSSIBLE NEGATIVE EFFECTS OF SOUTHWESTERLY SHEAR IN
ASSOCIATION WITH THE AFOREMENTIONED WEAKNESS OVER THE CENTRAL
ATLANTIC WHILE SEVERAL OF THE GLOBAL MODELS SHOW LESS SHEAR. THE
OFFICIAL NHC INTENSITY FORECAST IS A BIT LOWER EARLY IN THE PERIOD
GIVEN CURRENT TRENDS BUT REMAINS CLOSE TO BOTH THE PREVIOUS FORECAST
AND THE STATISTICAL-DYNAMICAL INTENSITY GUIDANCE. REGARDLESS OF THE
EXACT INTENSITY...GLOBAL MODELS ARE IN GOOD AGREEMENT THAT IGOR
WILL GROW IN SIZE...POTENTIALLY BECOMING A LARGE-SIZED HURRICANE.
 
 
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      10/0300Z 15.4N  28.0W    30 KT
 12HR VT     10/1200Z 15.9N  30.0W    30 KT
 24HR VT     11/0000Z 16.3N  33.1W    35 KT
 36HR VT     11/1200Z 16.5N  36.1W    40 KT
 48HR VT     12/0000Z 16.7N  39.0W    50 KT
 72HR VT     13/0000Z 17.5N  44.0W    65 KT
 96HR VT     14/0000Z 18.5N  48.0W    80 KT
120HR VT     15/0000Z 19.5N  50.5W    85 KT
 
$$
FORECASTER KIMBERLAIN/MUSHER
 
NNNN


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Page last modified: Friday, 15-Apr-2011 12:09:14 UTC