NHC Discussion
Posted by
Chris in Tampa on 9/8/2013, 4:48 pm
TROPICAL DEPRESSION NINE DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092013
500 PM AST SUN SEP 08 2013
SATELLITE IMAGES INDICATE THAT THE LOW PRESSURE SYSTEM BETWEEN THE
CAPE VERDE ISLANDS AND THE WEST COAST OF AFRICA HAS DEVELOPED
ENOUGH CONVECTIVE ORGANIZATION TO BE DESIGNATED AS A TROPICAL
DEPRESSION. THE INITIAL INTENSITY IS SET AT 25 KT BASED ON DVORAK
ESTIMATES OF T2.0 FROM TAFB AND T1.5 FROM SAB. THE LOW-LEVEL
CENTER APPEARS TO BE ON THE EASTERN EDGE OF THE DEEP CONVECTION DUE
TO A LITTLE BIT OF NORTHEASTERLY SHEAR.
THE INITIAL MOTION ESTIMATE IS 270/9 KT. THE DEPRESSION IS LOCATED
TO THE SOUTH OF A LARGE MID-TROPOSPHERIC ANTICYCLONE CENTERED NEAR
THE AZORES...AND THE CURRENT WESTWARD MOTION IS EXPECTED TO
CONTINUE FOR ANOTHER 36 HOURS OR SO. AFTER THAT TIME...THE
ANTICYCLONE IS FORECAST TO WEAKEN WHILE A CLOSED MID/UPPER-LEVEL
LOW DEVELOPS NEAR THE CANARY ISLANDS AND A RIDGE BUILDS WESTWARD
FROM AFRICA. THIS PATTERN WILL ALLOW THE DEPRESSION TO TURN RATHER
SHARPLY TO THE NORTH-NORTHWEST AFTER 48 HOURS AND CONTINUE THAT
TRAJECTORY THROUGH THE END OF THE FORECAST PERIOD. SURPRISINGLY...
THE LARGEST SPREAD AMONG THE TRACK GUIDANCE OCCURS WITHIN THE FIRST
48 HOURS OR SO...BUT THE MODELS SEEMS TO CONVERGE BY 72 HOURS. THE
NHC OFFICIAL TRACK FORECAST IS CLOSE TO THE MODEL CONSENSUS FOR
MUCH OF THE FORECAST.
A MOIST AIR MASS...WARM WATERS...AND RELATIVELY LIGHT SHEAR SHOULD
ALLOW THE DEPRESSION TO STRENGTHEN AT LEAST GRADUALLY DURING THE
NEXT FEW DAYS. HOWEVER...SOME OF THE MODELS...MAINLY THE
STATISTICAL-DYNAMICAL GUIDANCE...ARE FAIRLY AGGRESSIVE WITH THE
INTENSIFICATION RATE AFTER 24 HOURS. SHIPS AND LGEM HAVE TENDED TO
HAVE A HIGH BIAS THIS HURRICANE SEASON...SO THE OFFICIAL FORECAST
IS KEPT A BIT LOWER. THE FORECAST DOES...HOWEVER...ANTICIPATE THE
CYCLONE BECOMING A HURRICANE BY 72 HOURS.
GIVEN THE FORECAST...AND THE UNCERTAINTY WITH HOW BIG THE WIND FIELD
WILL GET ONCE THE DEPRESSION BECOMES A TROPICAL STORM...A TROPICAL
STORM WARNING HAS BEEN ISSUED FOR THE SOUTHERN CAPE VERDE ISLANDS.
FORECAST POSITIONS AND MAX WINDS
INIT 08/2100Z 13.1N 20.7W 25 KT 30 MPH
12H 09/0600Z 13.2N 22.1W 30 KT 35 MPH
24H 09/1800Z 13.5N 24.3W 35 KT 40 MPH
36H 10/0600Z 13.9N 26.5W 40 KT 45 MPH
48H 10/1800Z 14.5N 27.9W 55 KT 65 MPH
72H 11/1800Z 17.5N 29.5W 70 KT 80 MPH
96H 12/1800Z 21.0N 31.0W 70 KT 80 MPH
120H 13/1800Z 23.5N 32.5W 65 KT 75 MPH
$$
FORECASTER BERG
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