Tropical Depression SERGIO

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TROPICAL DEPRESSION SERGIO DISCUSSION NUMBER  28
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP212006
700 AM PST MON NOV 20 2006
 
CONVENTIONAL SATELLITE IMAGERY SHOWS PULSATING CONVECTION ACROSS THE
EASTERN SEMICIRCLE OF SERGIO.  THE PROXIMITY OF THE DEEP CONVECTION
TO THE CYCLONE'S CENTER YIELDED 1200 UTC DVORAK ESTIMATES FROM BOTH
TAFB AND AFWA OF 45 KT AND 35 KT FROM SAB.  SINCE THEN...THE
CONVECTION HAS PULLED FURTHER AWAY FROM THE CENTER ONCE AGAIN.
EARLY VISIBLE IMAGERY INDICATES A DISORGANIZED CLOUD PATTERN AND
PROVIDES LITTLE ADDITIONAL ASSISTANCE IN DISCERNING THE CENTER. MY
FIRST INCLINATION WAS TO BRING SERGIO BACK TO A TROPICAL STORM...
HOWEVER DUE TO THE WEAKENING CONVECTION AND LACK OF AN ORGANIZED
CENTER...THE INITIAL INTENSITY WILL REMAIN AT 30 KT. SOUTHWESTERLY
SHEAR AROUND 30 TO 35 KT IS CURRENTLY AFFECTING THE CYCLONE AND IS
FORECAST TO CONTINUE BUT BE SOMEWHAT MORE RELAXED.  EVEN IF THE
SHEAR DECREASES SIGNIFICANTLY AS INDICATED BY THE EXPERIMENTAL
SHIPS MODEL...WHICH REDUCES THE AREA THAT COMPUTES THE SHEAR...IT
WILL BE DIFFICULT FOR THE CIRCULATION TO RE-CONSOLIDATE.

THE INITIAL MOTION IS ESTIMATED AT 255/3.  SERGIO IS CURRENTLY
LOCATED TO THE SOUTH OF A LOW- TO MID-LEVEL RIDGE AND TO THE
NORTHEAST OF A LOW-LEVEL DISTURBANCE.  OVER THE NEXT COUPLE OF DAYS
THE RIDGE IS EXPECTED TO MIGRATE EASTWARD AND THE LOW-LEVEL
DISTURBANCE...WEST OF SERGIO...SHOULD CONTINUE WESTWARD.  THE
OFFICIAL FORECAST ANTICIPATES THAT SERGIO WILL REMAIN A SHALLOW
SYSTEM AND TAKES THE CYCLONE ON A GENERAL WESTWARD MOTION UNTIL
DISSIPATION OCCURS.  THE OFFICIAL FORECAST IS A LITTLE NORTH OF 
THE PREVIOUS TRACK AND FOLLOWS CLOSELY WITH THE MODEL CONSENSUS BUT
SLOWER.
 
FIRST LIGHT VISIBLE IMAGERY SUGGESTS THAT THE CENTER HAS BECOME EVEN
FURTHER DETACHED FROM THE CONVECTION THAN INDICATED...BUT I WILL
WAIT UNTIL THE NEXT ADVISORY TO DETERMINE IF SIGNIFICANT CHANGES...
SUCH AS DISSIPATING THE SYSTEM SOONER THAN INDICATED...ARE
WARRANTED.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      20/1500Z 14.9N 107.2W    30 KT
 12HR VT     21/0000Z 15.1N 107.7W    30 KT
 24HR VT     21/1200Z 15.4N 109.0W    30 KT
 36HR VT     22/0000Z 15.8N 110.8W    25 KT...REMNANT LOW
 48HR VT     22/1200Z 16.0N 112.5W    20 KT...REMNANT LOW
 72HR VT     23/1200Z...DISSIPATED
 
$$
FORECASTER MAINELLI
 
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