Tropical Storm GABRIELLE

...TROPICAL DEPRESSION FORMS SOUTH OF PUERTO RICO... ...TROPICAL STORM WARNINGS ISSUED...

5:00 PM AST Wed Sep 4
Location: 16.5°N 66.2°W
Moving: NW at 9 mph
Min pressure: 1009 mb
Max sustained: 35 mph

000
WTNT42 KNHC 042057
TCDAT2

TROPICAL DEPRESSION SEVEN DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072013
500 PM AST WED SEP 04 2013

AIRCRAFT AND SATELLITE DATA FROM THIS AFTERNOON INDICATE THAT THE
LOW PRESSURE SYSTEM SOUTH OF PUERTO RICO HAS JUST ENOUGH OF A
CIRCULATION AND ORGANIZED CONVECTION TO BE CONSIDERED A TROPICAL
DEPRESSION. THE INITIAL INTENSITY IS SET TO 30 KT BASED ON A 41 KT
FLIGHT-LEVEL WIND FROM THE AIR FORCE PLANE.

THE ENVIRONMENT NEAR THE DEPRESSION APPEARS TO BE CONDUCIVE FOR
STRENGTHENING DURING THE NEXT DAY OR SO WHILE IT REMAINS FAR ENOUGH
AWAY FROM HISPANIOLA. ONLY GRADUAL INTENSIFICATION IS FORECAST DUE
TO THE SOMEWHAT DISORGANIZED INITIAL STATE OF THE DEPRESSION. AFTER
THAT TIME...A COMBINATION OF INCREASING VERTICAL WIND SHEAR AND
POSSIBLE LAND INTERACTION COULD SLOW THE DEVELOPMENT OF THE
CYCLONE. THE NHC FORECAST IS ON THE LOW SIDE OF THE GUIDANCE
ENVELOPE...AND IS CLOSER TO THE SHIPS AND LGEM MODELS. THE
WIND SPEED PREDICTION ALSO FITS THE GENERAL IDEA OF THE GLOBAL
MODELS...WHICH SUGGEST THAT THE CYCLONE WILL STRUGGLE AFTER IT
LEAVES THE CARIBBEAN SEA. SOME INTENSIFICATION...PERHAPS DUE TO
BAROCLINIC PROCESSES...IS POSSIBLE AT LONG RANGE AS THE CYCLONE
INTERACTS WITH A MID-LATITUDE TROUGH.

THE DEPRESSION APPEARS TO BE MOVING ROUGHLY 305/8 AROUND THE
SOUTHWESTERN PERIPHERY OF A MID-LEVEL RIDGE OVER THE CENTRAL
ATLANTIC OCEAN. A LARGE TROUGH OVER THE WESTERN ATLANTIC OCEAN IS
EXPECTED TO CAUSE THE RIDGE TO BREAK ALONG ABOUT 70W...WHICH SHOULD
CAUSE THE CYCLONE TO TURN NORTHWARD IN TWO OR THREE DAYS. ONE
COMPLICATING FACTOR IS THE LARGER DISTURBANCE LOCATED A FEW HUNDRED
MILES NORTHEAST OF THE DEPRESSION. THE INTERACTION OF THESE TWO
FEATURES MAKES THIS TRACK FORECAST MORE UNCERTAIN THAN WOULD BE
SUGGESTED BY THE OVERALL MODEL SPREAD. THE NHC FORECAST IS NOT TOO
FAR FROM THE MODEL CONSENSUS EARLY ON...AND THEN IS A BIT SLOWER
THAN THE CONSENSUS AFTER THAT TIME...PUTTING LESS WEIGHT ON THE
NORTHWARD GFDL/HWRF SOLUTIONS.



FORECAST POSITIONS AND MAX WINDS

INIT 04/2100Z 16.5N 66.2W 30 KT 35 MPH
12H 05/0600Z 17.4N 67.1W 35 KT 40 MPH
24H 05/1800Z 18.6N 68.1W 40 KT 45 MPH
36H 06/0600Z 19.7N 68.8W 40 KT 45 MPH
48H 06/1800Z 20.9N 69.2W 40 KT 45 MPH
72H 07/1800Z 23.1N 69.4W 45 KT 50 MPH
96H 08/1800Z 25.3N 68.9W 45 KT 50 MPH
120H 09/1800Z 29.0N 65.0W 50 KT 60 MPH

$$
FORECASTER BLAKE