[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 201149
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT SUN SEP 20 2009

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0945 UTC.

...SPECIAL FEATURES...

A 1011 MB LOW IS CENTERED E OF THE WINDWARD ISLANDS NEAR 15N45W
MOVING TO THE WNW NEAR 9 KT. SCATTERED MODERATE CONVECTION IS
FROM 14N-16N BETWEEN 44W-49W. WHILE THE SYSTEM REMAINS POORLY
ORGANIZED...IT HAS A MEDIUM CHANCE...30 TO 50 PERCENT...OF
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HRS.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 32W/33W S OF 19N MOVING W NEAR 12 KT. THE
WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN
TOTAL PRECIPITABLE WATER IMAGERY AS WELL AS A MAXIMUM IN 850 MB
RELATIVE VORTICITY SEEN IN THE CIMSS WAVETRAK MODEL GUIDANCE. NO
DEEP CONVECTION IS CURRENTLY ASSOCIATED WITH THE WAVE.

TROPICAL WAVE IS ALONG 96W S OF 20N MOVING W NEAR 10 KT. THE
WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM IN THE E
PACIFIC BASIN WHERE MOST OF THE WAVE AXIS LIES. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS S OF 21N BETWEEN 95W-98W.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 11N15W 13N30W 16N43W 12N48W
10N63W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM
15N-17N BETWEEN 39W-42W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 0900 UTC...A SURFACE TROUGH EXTENDS ACROSS THE SE GULF
FROM 27N83W TO THE YUCATAN PENINSULA NEAR 21N87W. ISOLATED
SHOWERS/THUNDERSTORMS ARE WITHIN 150 NM EITHER SIDE OF THE
TROUGH AXIS. THIS ACTIVITY IS ALSO ENHANCED BY UPPER LEVEL
DIFFLUENCE BETWEEN A SHORTWAVE UPPER LEVEL TROUGH OVER THE N
CENTRAL GULF WITH AXIS ALONG 87W AND AN UPPER LEVEL RIDGE OVER
THE SE GULF CENTERED OVER THE STRAIGHTS OF FLORIDA NEAR 24N80W.
ISOLATED SHOWERS/THUNDERSTORMS ARE ALSO ACROSS THE SW GULF S OF
22S W OF 89W IN ASSOCIATION WITH UPPER LEVEL DIFFLUENCE BETWEEN
THE SHORTWAVE UPPER TROUGH OVER THE CENTRAL GULF AND ANOTHER
UPPER LEVEL RIDGE OVER THE WRN GULF CENTERED OVER MEXICO NEAR
21N103W. SCATTERED SHOWERS/THUNDERSTORMS IN THE FAR SW GULF ARE
ALSO ENHANCED BY SURFACE CONVERGENCE NEAR THE TROPICAL WAVE
ALONG 96W...SEE ABOVE. EXPECT A SURFACE RIDGE TO BUILD E TO W BY
MON.

CARIBBEAN SEA...
AS OF 0900 UTC...A SURFACE TROUGH EXTENDS OVER THE NW CARIBBEAN
FROM 19N84W TO 11N83W. ISOLATED SHOWERS/THUNDERSTORMS ARE FROM
14N-22N BETWEEN W OF 78W. THE ACTIVITY IS ENHANCED BY SURFACE
CONVERGENCE NEAR THE TROUGH AS WELL AS UPPER LEVEL DIFFLUENCE
BETWEEN AN UPPER LEVEL RIDGE OVER THE SE GULF AND THE BAHAMAS
CENTERED OVER THE STRAIGHTS OF FLORIDA NEAR 24N80W AND AN UPPER
LEVEL INVERTED TROUGH OVER THE NW CARIBBEAN AND CENTRAL AMERICA.
THE REMAINDER OF THE CENTRAL AND E CARIBBEAN REMAINS FAIRLY CALM
UNDER THE INFLUENCE OF DRY AIR ALOFT. HOWEVER...A FEW ISOLATED
SHOWERS/THUNDERSTORMS ARE S OF WRN HISPANIOLA FROM 17N-18N
BETWEEN 71W-74W DUE TO UPPER LEVEL DIFFLUENT FLOW BETWEEN THE
UPPER LEVEL RIDGE OVER THE BAHAMAS AND AN UPPER LEVEL LOW N OF
THE WINDWARD ISLANDS NEAR 23N62W. ISOLATED SHOWERS/THUNDERSTORMS
ARE ALSO ACROSS PUERTO RICO N OF 17N BETWEEN 66W-68W IN
ASSOCIATION WITH THE AFOREMENTIONED UPPER LEVEL LOW N OF THE
WINDWARD ISLANDS. FRESH TRADE WINDS ARE ACROSS THE SRN CARIBBEAN
WITH THE STRONGEST NEAR THE COAST OF COLOMBIA. EXPECT
SHOWERS/THUNDERSTORMS TO PERSIST OVER THE WRN CARIBBEAN AS THE
UPPER LEVEL TROUGH OVER THE W CARIBBEAN MOVES W.

ATLANTIC OCEAN...
A FEW ISOLATED SHOWERS REMAIN ACROSS THE FAR WRN ATLC FROM
24N-29N W OF 78W DUE TO UPPER LEVEL DIFFLUENT FLOW BETWEEN AN
UPPER LEVEL RIDGE OVER THE BAHAMAS CENTERED OVER THE STRAITS OF
FLORIDA NEAR 24N80W AND A SHORTWAVE UPPER LEVEL TROUGH ACROSS
THE N CENTRAL GULF. A 1014 MB SURFACE LOW IS NEAR 28N71W WITH A
SURFACE TROUGH EXTENDING THROUGH IT FROM 31N70W TO 25N71W.
SURFACE CONVERGENCE NEAR THE LOW AND TROUGH AXIS IS SUPPORTING
SCATTERED SHOWERS/THUNDERSTORMS FROM 25N-28N BETWEEN 70W-72W. A
SURFACE TROUGH EXTENDS FROM 26N58W TO 21N61W. ISOLATED SHOWERS
ARE WITHIN 50 NM EITHER SIDE OF THE TROUGH AXIS. THE TROUGH IS
SUPPORTED BY AN UPPER LEVEL LOW NEAR 23N62W. IS
SHOWERS/THUNDERSTORMS ARE ALSO N OF THE WINDWARD ISLANDS FROM
18N-20N BETWEEN 62W-68W IN ASSOCIATION WITH THE UPPER LOW.
ELSEWHERE ACROSS THE ATLC...A BROAD SURFACE RIDGE DOMINATES
ANCHORED BY A 1025 MB HIGH NEAR 33N42W. IN THE UPPER LEVELS...AN
UPPER LEVEL RIDGE IS N OF 26N BETWEEN 34W-47W. AN UPPER LEVEL
TROUGH DOMINATES THE E ATLC WITH AXIS ALONG 33N25W TO 23N35W.
UPPER LEVEL DIFFLUENCE ON THE E SIDE OF THE TROUGH IS SUPPORTING
ISOLATED SHOWERS FROM 23N-30N E OF 22W. A BROAD UPPER LEVEL
RIDGE COVERS THE TROPICAL ATLC ENHANCING CONVECTION NEAR THE LOW
CENTERED AT 15N45W.

$$
WALTON



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