TROPICAL DEPRESSION NINE DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092012
500 AM AST TUE AUG 21 2012

THE LARGE LOW PRESSURE SYSTEM THAT HAS BEEN TRAVERSING THE CENTRAL
TROPICAL ATLANTIC FOR THE PAST FEW DAYS HAS ACQUIRED ENOUGH
ORGANIZED DEEP CONVECTION NEAR THE CENTER TO BE CLASSIFIED AS A
TROPICAL DEPRESSION. THE INITIAL INTENSITY OF 30 KT IS BASED ON A
SATELLITE INTENSITY ESTIMATE OF T2.0/30 KT FROM TAFB AND T1.5/25 KT
FROM SAB. SINCE THE 0600 UTC SATELLITE CLASSIFICATIONS…
CONVECTION HAS CONTINUED TO INCREASE WITH SOME CLOUD TOP
TEMPERATURES COLDER THAN -80C NOTED JUST SOUTHWEST OF THE LOW-LEVEL
CENTER.

THE INITIAL MOTION ESTIMATE IS 270/17 KT. THE DEPRESSION IS LOCATED
SOUTH OF A DEEP-LAYER SUBTROPICAL RIDGE THAT IS FORECAST TO REMAIN
INTACT FOR THE NEXT FOUR DAYS…WHICH SHOULD KEEP THE CYCLONE
MOVING IN A WESTWARD TO WEST-NORTHWESTWARD DIRECTION THROUGH 96
HOURS. BY DAY 5…HOWEVER…THE GLOBAL MODELS ARE FORECASTING A
SHORTWAVE TROUGH TO DIG SOUTHWARD OVER THE SOUTHEASTERN U.S. AND
THE GULF OF MEXICO…WHICH IS EXPECTED TO WEAKEN THE RIDGE ACROSS
FLORIDA AND THE BAHAMAS. THIS SHOULD ALLOW THE CYCLONE TO TURN
NORTHWESTWARD AND SLOW DOWN ACROSS THE NORTH-CENTRAL CARIBBEAN SEA.
THE OFFICIAL FORECAST TRACK IS CLOSE TO THE MULTI-MODEL CONSENSUS
TVCA…WHICH IS A COMPROMISE OF THE FASTER GFS MODEL AND SLOWER
ECMWF MODEL.

OTHER THAN SOME MODEST NORTHEASTERLY VERTICAL WIND SHEAR FOR THE
NEXT 24 HOURS OR SO…ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE
QUITE FAVORABLE FOR INTENSIFICATION TO OCCUR. DURING DAYS 2-3…THE
VERTICAL SHEAR IS FORECAST TO BE THE WEAKEST AND WATER TEMPERATURES
THE WARMEST…AND THAT IS WHEN THE MOST SIGNIFICANT STRENGTHENING
SHOULD OCCUR. AT DAYS 4 AND 5…POSSIBLE INTERACTION WITH LAND
MASSES OF HAITI AND CUBA…RESPECTIVELY…IS THE PRIMARY REASON
FOR THE LEVELING OFF IN THE INTENSITY. THE OFFICIAL INTENSITY
FORECAST CLOSELY FOLLOWS THE TREND OF…BUT IS LOWER THAN…THE
SHIPS AND LGEM INTENSITY MODELS…ESPECIALLY AT DAYS 3 AND 4.

AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT WILL INVESTIGATE THE
CYCLONE THIS AFTERNOON.