[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 111746
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT TUE SEP 11 2007

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN
SECTIONS OF SOUTH AMERICA...AND THE ATLANTIC OCEAN TO THE
AFRICAN COAST FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION
IS BASED ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...
WEATHER OBSERVATIONS...AND RADAR.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURE...
GABRIELLE IS DISSIPATING WELL SOUTH OF NOVA SCOTIA. AS OF
11/1500 UTC THE CENTER OF THE DEPRESSION WAS NEAR 39.6N 65.3W OR
ABOUT 310 NM SOUTH-SOUTHWEST OF HALIFAX NOVA SCOTIA. GABRIELLE
IS MOVING EAST-NORTHEAST AT 19 KT. MAXIMUM SUSTAINED WINDS
REMAIN NEAR 30 KT WITH GUSTS TO 40 KT. THE ESTIMATED MINIMUM
CENTRAL PRESSURE IS 1008 MB. THUNDERSTORM ACTIVITY CONTINUES
OVER THE SOUTHEASTERN PORTION OF GABRIELLE. HOWEVER...A 1000 UTC
QUIKSCAT OVERPASS INDICATES THAT THE CIRCULATION HAS BECOME
ILL-DEFINED AND ELONGATED SOUTHEAST TO NORTHWEST. SINCE A
WELL-DEFINED SURFACE CIRCULATION NO LONGER EXISTS...THIS SYSTEM
NO LONGER QUALIFIES AS A TROPICAL CYCLONE. THEREFORE...THE LAST
PUBLIC ADVISORY WAS ISSUED BY THE NATIONAL HURRICANE CENTER ON
THIS SYSTEM AT 1500 UTC.

SHOWER AND THUNDERSTORM ACTIVITY HAS DECREASED THIS MORNING IN
ASSOCIATION WITH A TROPICAL WAVE AND BROAD AREA OF LOW PRESSURE
LOCATED NEAR 11N41W OR ABOUT 1085 NM EAST OF THE WINDWARD
ISLANDS. HOWEVER...CONDITIONS APPEAR FAVORABLE FOR DEVELOPMENT
AND THIS SYSTEM COULD STILL BECOME A TROPICAL DEPRESSION WITHIN
A DAY OR TWO AS IT MOVES WEST-NORTHWESTWARD ABOUT 10 MPH. THE
HOVMOLLER DIAGRAM SHOWS VERY CLEAR THE SLOW WWD PROPAGATION OF
THIS SYSTEM.

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 28W S OF 22N MOVING W 15 KT. THIS
REMAINS A LARGE AMPLITUDE WAVE WITH VISIBLE SATELLITE IMAGERY
INDICATING BROAD TURNING IN THE STRATOCUMULUS FIELD BETWEEN 27W
AND 35W. WHILE THE WAVE STRUCTURE IS WELL DEFINED...CONVECTION
REMAINS CONFINED WELL TO THE SW OF THE AXIS WITHIN THE
INTERSECTION OF THE ITCZ FROM 10N-13N BETWEEN 29W-33W.

A TROPICAL WAVE IS IN THE E CARIB ALONG 67W/68W S OF 20N MOVING
W 10 TO 15 KT. A WEAK INVERTED-V SIGNATURE IS SEEN ON VISIBLE
SATELLITE IMAGERY. THE WAVE IS INTERACTING WITH A BROAD UPPER
LOW THAT IS SOUTH OF HISPANIOLA. MOISTURE FROM THIS WAVE WILL
COMBINE WITH THE LOCAL EFFECTS TO GENERATE SOME SHOWER/TSTM
ACTIVITY OVER PUERTO RICO THIS AFTERNOON AND EARLY EVENING.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 11N15W 12N30W 12N40W 8N47W 11N61W.
BESIDES FOR THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES
AND BROAD AREA OF LOW PRES...ISOLATED MODERATE CONVECTION IS
FROM 6N-1-N BETWEEN 20W-29W. CLUSTERS OF MODERATE TO ISOLATED
STRONG CONVECTION ARE APPROACHING THE WEST COAST OF AFRICA
PROBABLY ASSOCIATED WITH THE NEXT TROPICAL WAVE.

DISCUSSION...

THE GULF OF MEXICO...
THE MAIN FEATURE IN THE GULF IS A 1011 MB LOW PRES SYSTEM
CENTERED NEAR 26N95W. A TROUGH EXTENDS MAINLY SOUTH FROM THE LOW
TO THE BAY OF CAMPECHE...WHERE THERE WAS A CLUSTER OF SCATTERED
MODERATE TO STRONG CONVECTION THIS MORNING. ANOTHER SFC TROUGH
EXTENDS NE FROM THE LOW TO SE LOUISIANA. THIS LOW AND TROUGH
SHOW UP NICELY IN THE SHIP...BUOY AND EARLIER QSCAT DATA. CU
LINES ALSO DEFINE THE POSITION OF THE LOW OVER THE NW CORNER OF
THE GULF. UPPER-LEVEL WINDS HAVE BECOME A LITTLE MORE FAVORABLE
FOR DEVELOPMENT. HOWEVER...DEVELOPMENT...IF ANY...SHOULD BE SLOW
TO OCCUR DUE TO PROXIMITY TO LAND. SCATTERED SHOWERS AND TSTMS
ARE N OF 24N WEST OF 90W RELATED TO THIS LOW. SIMILAR CONVECTION
IS OBSERVED ALONG THE N GULF WATERS...INCLUDING THE COAST OF
LOUISIANA AND THE FLORIDA PANHANDLE. AN UPPER LOW OVER THE NE
GULF CENTERED NEAR 27N84W IS ENHANCING THIS ACTIVITY. A WEAK
COLD FRONT IS APPROACHING THE COAST OF TEXAS. THE FRONT WILL
STALL BRIEFLY OVER THE NW GULF WATERS WED THEN DRIFT W THU AND
FRI AS A RIDGE BUILDS W OVER NORTHERN GULF.

THE CARIBBEAN SEA...
A BROAD UPPER LEVEL LOW IS OVER THE BASIN JUST SOUTH OF
HISPANIOLA. THIS FEATURE HAS BEEN DRIFTING SLOWLY W. DIFFLUENCE
BETWEEN THIS SYSTEM AND AN UPPER HIGH LOCATED E OF THE LESSER
ANTILLES...ALONG WITH THE TROPICAL WAVE MENTIONED ABOVE IS
SUPPORTING AN AREA OF CLOUDINESS WITH SCATTRED SHOWERS AND TSTMS
THAT IS AFFECTING THE SRN WINDWARD ISLANDS AND NE VENEZUELA. A
DIFFLUENT PATTERN ALOFT BETWEEN A RIDGE COVERING THE NW
CARIBBEAN AND CENTRAL AMERICA AND THE AFOREMENTIONED LOW IS
HELPING TO INDUCE SOME SHOWER/TSTM ACTIVITY OVER THE SW
CARIBBEAN...THE CARIBBEAN PLAINS OF NICARAGUA AND NE HONDURAS.
MUCH DRIER AIR LIES OVER THE CENTRAL CARIB WITHIN THE
CIRCULATION OF THE UPPER LOW. TRADE WINDS HAVE INCREASED A BIT
SINCE YESTERDAY WITH AN EARLIER QSCAT PASS SHOWING A SOLID AREA
OF 20-25 KT WINDS BETWEEN COLOMBIA AND HISPANIOLA.

THE ATLANTIC OCEAN...
THE SUBTROPICAL RIDGE IS BUILDING WWD ACROSS FLORIDA AND THE
GULF. A 1022 MB HIGH CENTER IS LOCATED NEAR 32N60W. THE PRES
GRADIENT IS TIGHTENED BETWEEN THIS HIGH AND THE SEMI-PERMANENT
LOW LOCATED OVER N COLOMBIA. AS A RESULT...THE TRADE WINDS HAVE
INCREASED ACROSS THE CARIBBEAN SEA. THIS WEATHER PATTERN WILL
PERSIST DURING THE NEXT FEW DAYS. ANOTHER 1022 MB HIGH IS
SITUATED NEAR 32N28W. IN BETWEEN...A WEAK SFC TROUGH CLIPS THE
FORECAST AREA NEAR 30N44W.

IN THE MID AND UPPER LEVELS...RIDGING IS THE PATTERN ACROSS THE
W ATLC N OF 26N W OF 67W. TROUGHING TAKES OVER S OF 26N
ASSOCIATED WITH THE NRN EXTENSION OF THE CARIBBEAN UPPER LOW.
A DEEP LAYER TROUGH IS OVER THE CENTRAL ATLC AND ROUGHLY
COVERS THE AREA N OF 25N BETWEEN 35W-65W. DIFFLUENCE BETWEEN ALL
OF THESE UPPER SYSTEMS HAS GENERATED A BAND OF SHOWERS WITH
EMBEDDED TSTMS ALONG 24N BETWEEN 59W-74W. UPPER RIDGING
DOMINATES THE REMAINDER OF THE ATLANTIC OCEAN WITH A PAIR OF
ANTICYCLONES. ONE IS LOCATED E OF THE LESSER ANTILLES NEAR
15N50W. THE SECOND ONE IS NEAR 20N36W.

$$
GR





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