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TROPICAL DEPRESSION ELEVEN-E DISCUSSION NUMBER 7
NATIONAL WEATHER SERVICE MIAMI FL
2 AM PDT SAT SEP 07 2002
THE CENTER OF THE DEPRESSION IS DIFFICULT TO LOCATE WITH
CONVENTIONAL SATELLITE IMAGERY...BUT IT APPEARS THAT THE CYCLONE HAS
SLOWED DOWN CONSIDERABLY DURING THE PAST 6 HOURS. EARLIER MICROWAVE
DATA INDICATED A TIGHT CIRCULATION WHEN THE SYSTEM PROBABLY PEAKED
BETWEEN 21Z AND 00Z. HOWEVER...CONVECTION HAS DECREASED MARKEDLY
SINCE THEN. THE PREVIOUS INTENSITY OF 30 KT IS MAINTAINED FOR THIS
ADVISORY BASED ON SATELLITE INTENSITY ESTIMATES OF 30 KT...35 KT...
AND 25 KT FROM TAFB...SAB...AND AFWA...RESPECTIVELY. THE CENTRAL
PRESSURE WAS LOWERED TO 1006 MB BASED ON SHIP REPORTS LOCATED
NORTHEAST AND SOUTHWEST OF THE CENTER REPORTING 1007.2 MB AT 00Z.
THE INITIAL MOTION ESTIMATE IS 320/03. DUE TO THE UNCERTAINTY IN THE
CENTER POSITION...I DID NOT WANT TO MAKE ANY SIGNIFICANT CHANGES TO
THE PREVIOUS FORECAST TRACK OTHER THAN TO SLOW DOWN THE FORWARD
SPEED. THE OUTER CIRCULATION IS FAIRLY WELL-DEFINED...BUT THE
INNER-CORE WIND FIELD REMAINS POORLY DEFINED DUE TO THE LACK OF DEEP
CONVECTION. THE NHC MODEL GUIDANCE IS IN STRONG AGREEMENT ON THE
CYCLONE TRACKING NORTHWESTWARD FOR 24 TO 36 HOURS AND THEN MORE
NORTHWARD AFTER THAT...EXCEPT FOR THE GFDL MODEL WHICH DISSIPATES
THE SYSTEM WITHIN 12 HOURS. THE OFFICIAL FORECAST TRACK IS JUST AN
UPDATE OF THE PREVIOUS TRACK...ALBEIT SLOWER...AND IS IN THE MIDDLE
OF THE TIGHTLY PACKED MODEL SUITE.
IT APPEARS THAT THE DEPRESSION HAS MISSED ITS OPPORTUNITY FOR
SIGNIFICANT INTENSIFICATION TO OCCUR. WHILE SSTS ARE WARM...AROUND
28C...AND THE SHEAR IS LOW...AROUND 5 KT...THE PRESENCE OF DRY
MID-LEVEL AIR SURROUNDING THE CYCLONE IS THE LIKELY CULPRIT THAT HAS
CAUSED THE CONVECTION TO SIGNIFICANTLY WEAKEN. THERE MAY BE
INTERMITTENT BURSTS OF CONVECTION THAT WILL SPIN UP THE INNER-CORE
WIND FIELD OVER THE NEXT 24 TO 36 HOURS...BUT THAT WILL LIKELY JUST
RESULT IN THE MORE DRY AIR BEING ENTRAINED CAUSING THE CONVECTION TO
WEAKEN AGAIN. HOWEVER...OUT OF RESPECT FOR THE SHIPS INTENSITY MODEL
AND THE FACT THAT THE CYCLONE IS FORECAST TO REMAIN OVER WARM SSTS
FOR ANOTHER 24 HOURS...THE OFFICIAL INTENSITY FORECAST CALLS FOR
SOME SLIGHT STRENGTHENING THROUGH 24 HOURS. AFTERWARDS...GRADUAL
WEAKENING IS EXPECTED SINCE THE SYSTEM WILL BE MOVING OVER MUCH
COOLER WATER. HOWEVER...IF CONVECTION DOES NOT REDEVELOP NEAR THE
LOW-LEVEL CENTER WITHIN THE NEXT 12 HOURS OR SO...THEN THE
DEPRESSION COULD DISSIPATE LATER TODAY LIKE THE GFDL MODEL IS
FORECASTING.
FORECASTER STEWART/BERG
FORECAST POSITIONS AND MAX WINDS
INITIAL 07/0900Z 21.7N 111.6W 30 KTS
12HR VT 07/1800Z 22.3N 112.1W 35 KTS
24HR VT 08/0600Z 23.5N 112.8W 40 KTS
36HR VT 08/1800Z 24.8N 113.5W 35 KTS
48HR VT 09/0600Z 26.2N 114.0W 30 KTS
72HR VT 10/0600Z 29.0N 115.0W 25 KTS
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