[Tropical] Tropical Cyclone Discussion

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WTNT44 KNHC 070857
TCDAT4
TROPICAL STORM COLIN DISCUSSION NUMBER  14
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL042010
500 AM AST SAT AUG 07 2010

DATA FROM THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT SHOW THAT
COLIN REMAINS POORLY ORGANIZED...WITH THE THE SURFACE CENTER
DISPLACED NORTH OF THE 850-MB FLIGHT LEVEL CENTER FIX.  THE HIGHEST
FLIGHT LEVEL AND SFMR WINDS SAMPLED BY THE AIRCRAFT WERE 36 KT.
THE INITIAL INTENSITY WILL BE HELD GENEROUSLY AT 40 KT FOR THIS
PACKAGE...ASSUMING SOME HIGHER WINDS REMAIN IN THE DEEP CONVECTION
TO THE SOUTHEAST OF THE CENTER.

THE OUTFLOW HAS BECOME RESTRICTED IN THE NORTHEASTERN QUADRANT OVER
THE PAST FEW HOURS...AND DEEP CONVECTION IS NOW CONFINED TO THE
SOUTHEASTERN QUADRANT.  WHILE THE SHIPS MODEL ANALYZES ONLY ABOUT
10 KT OF SHEAR OVER COLIN...SATELLITE IMAGERY SUGGESTS THAT SHEAR
AND DRY AIR CONTINUE TO INHIBIT DEEP CONVECTION WEST AND NORTH OF
THE CENTER. SHIPS SHOWS THE SHEAR REMAINING LOW FOR THE NEXT 24
HOURS...WHICH MAY ALLOW FOR SOME STRENGTHENING AS COLIN WILL REMAIN
OVER WARM WATERS AND IN A DIVERGENT UPPER-LEVEL ENVIRONMENT. AFTER
48 HOURS...THE SHEAR INCREASES RAPIDLY AND COLIN SHOULD GRADUALLY
WEAKEN AS THE CYCLONE MOVES OVER COOLER WATERS AND BECOMES
EXTRATROPICAL. THE NEW NHC INTENSITY FORECAST IS IN BEST AGREEMENT
WITH ICON.

SATELLITE IMAGERY AND DATA FROM THE AIRCRAFT INDICATE THAT COLIN HAS
MOVED VERY SLOWLY NORTHWARD FOR THE PAST SEVERAL HOURS WITH AN
INITIAL MOTION ESTIMATE OF 010/04.  COLIN APPEARS TO BE CAUGHT IN A
REGION OF WEAK STEERING FLOW ON THE WESTERN EDGE OF THE WEAKENING
SUBTROPICAL RIDGE. THE TRACK GUIDANCE IS INSISTENT ON COLIN
ACCELERATING NORTH-NORTHEASTWARD AS THE RIDGE REBUILDS TO THE EAST
AND A LONGWAVE TROUGH MOVES OFF THE COAST OF THE NORTHEASTERN
UNITED STATES. AT 48 HOURS AND BEYOND...AN ACCELERATION TOWARD THE
NORTHEAST IS EXPECTED AS COLIN IS CAUGHT UP IN THE MID-LATITUDE
FLOW. MOST OF THE GUIDANCE IS IN GOOD AGREEMENT ON THE DIRECTION OF
MOTION...BUT THERE IS SOME DISAGREEMENT IN THE FORWARD SPEED. THE
NEW NHC FORECAST IS SLOWER THAN THE PREVIOUS ONE FOR THE FIRST 12
TO 24 HOURS DUE TO THE INITIAL MOTION...AND IS LARGELY AN UPDATE OF
THE PREVIOUS PACKAGE BEYOND THAT TIME...IN BEST AGREEMENT WITH THE
ECMWF.

FORECAST POSITIONS AND MAX WINDS

INITIAL      07/0900Z 29.1N  66.5W    40 KT
 12HR VT     07/1800Z 30.4N  66.0W    40 KT
 24HR VT     08/0600Z 32.3N  65.0W    45 KT
 36HR VT     08/1800Z 34.8N  63.9W    50 KT
 48HR VT     09/0600Z 37.8N  61.9W    55 KT
 72HR VT     10/0600Z 44.0N  54.0W    50 KT
 96HR VT     11/0600Z 51.5N  43.0W    45 KT...POST-TROP/EXTRATROP
120HR VT     12/0600Z...DISSIPATED

$$
FORECASTER BRENNAN


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