[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 201749
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 33W S OF 17N MOVING W NEAR 12 KT. THE
WAVE RESIDES IN AN AREA OF DEEP LAYER MOISTURE ACROSS THE ERN
ATLC AS OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. CIMSS
WAVETRAK MODEL GUIDANCE INDICATES A MAXIMUM IN 850 MB RELATIVE
VORTICITY IN THE VICINITY OF THE WAVE AXIS BUT THIS RELATIVE
VORTICITY STRETCHES FROM NE OF A 1012 MB LOW NEAR 16N46W EWD TO
24W NEAR THE CAPE VERDE ISLANDS. THEREFORE...A HIGH LEVEL OF
UNCERTAINTY IS PLACED IN THE POSITION OF THE WAVE AT THIS TIME
AND IS BASED MORE ON EXTRAPOLATION. NO DEEP CONVECTION IS
CURRENTLY ASSOCIATED WITH THE WAVE.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 8N13W 6N20W 8N30W 11N35W 12N41W
11N49W 10N62W. WIDELY SCATTERED MODERATE CONVECTION IS FROM
4N-8N BETWEEN 13W-22W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 1500 UTC...A SURFACE TROUGH EXTENDS ACROSS THE SE GULF
FROM 27N83W TO THE YUCATAN PENINSULA NEAR 22N87W. ISOLATED
SHOWERS AND TSTMS ARE WITHIN 90 NM EITHER SIDE OF THE TROUGH
AXIS. THIS ACTIVITY IS ALSO ENHANCED BY UPPER LEVEL DIFFLUENCE
BETWEEN AN UPPER LEVEL TROUGH OVER THE NE GULF WITH AXIS ALONG
86W AND AN UPPER LEVEL RIDGE OVER THE SE GULF CENTERED OVER THE
STRAITS OF FLORIDA NEAR 24N80W. ACROSS THE SW GULF...ISOLATED
SHOWERS AND TSTMS ARE S OF 24N W OF 90W IN ASSOCIATION WITH
UPPER LEVEL DIFFLUENCE CAUSED BY AN UPPER LEVEL RIDGE W OF 89W.
THIS UPPER LEVEL RIDGE IS ANCHORED OVER W/CENTRAL MEXICO NEAR
20N105W. OTHERWISE...THE GULF REMAINS UNDER LIGHT ELY SURFACE
FLOW THIS AFTERNOON.

CARIBBEAN SEA...
AN UPPER LEVEL TROUGH EXTENDS ACROSS THE GULF OF HONDURAS AND
THE NW CARIBBEAN. LOW-LEVEL CONVERGENCE AND LIFT PROVIDED BY THE
UPPER TROUGH IS GENERATING SCATTERED SHOWERS AND TSTMS FROM
19N-22N BETWEEN 82W-88W. SCATTERED SHOWER ACTIVITY EXTENDS
FARTHER SOUTH FROM 15N-19N BETWEEN 80W-89W. ACROSS THE SW
CARIBBEAN...AN UPPER LEVEL DIFFLUENT ENVIRONMENT IS IN PLACE DUE
TO UPPER LEVEL TROUGHING ACROSS THE E PACIFIC AND UPPER LEVEL
RIDGING OVER NRN SOUTH AMERICA. STRONG SLY DIFFLUENT FLOW OVER
PANAMA AND THE SW CARIBBEAN IS SUPPORTING SCATTERED SHOWERS AND
ISOLATED TSTMS SW OF A LINE FROM 13N84W TO 9N76W. ELSEWHERE
ACROSS THE REMAINDER OF THE CARIBBEAN...PRIMARILY E OF 74W...
UPPER LEVEL TROUGHING EXTENDS OVER THE BASIN FROM AN UPPER LEVEL
LOW CENTERED OVER THE CENTRAL ATLC NEAR 25N59W. CONDITIONS
REMAIN GENERALLY FAIR UNDER THE INFLUENCE OF DRY AIR ALOFT AS
NOTED ON WATER VAPOR IMAGERY. HOWEVER...A FEW ISOLATED SHOWERS
ARE OCCURRING ACROSS PORTIONS OF HISPANIOLA...PUERTO RICO AND
THE US/UK VIRGIN ISLANDS DUE TO THE MAIN AXIS OF CYCLONIC
CURVATURE LOCATED ALOFT OVER THE ERN MOST GREATER ANTILLES.
FARTHER TO THE SE...A FEW PASSING ISOLATED SHOWERS ARE NOTED ON
SATELLITE IMAGERY ACROSS THE WINDWARD ISLANDS THIS AFTERNOON.

ATLANTIC OCEAN...
A FEW ISOLATED SHOWERS ARE ACROSS THE FAR WRN ATLC N OF 24N W OF
78W DUE TO UPPER LEVEL DIFFLUENT FLOW BETWEEN AN UPPER LEVEL
RIDGE EXTENDING FROM THE FLORIDA STRAITS OVER THE NW BAHAMAS TO
27N73W AND AN UPPER LEVEL SHORTWAVE TROUGH ACROSS THE NE GULF.
THE UPPER LEVEL SHORTWAVE TROUGH LINKS UP WITH A LARGER UPPER
LEVEL TROUGH ACROSS THE NW ATLC...N OF THE DISCUSSION AREA...AND
THIS TROUGH SUPPORTS A COLD FRONT THAT ENTERS THE AREA NEAR
32N65W EXTENDING ALONG 31N TO 80W. A PRE-FRONTAL TROUGH IS
ANALYZED FROM 31N70W THROUGH A 1015 MB LOW NEAR 28N71W TO NEAR
25N72W. SCATTERED SHOWERS AND TSTMS ARE S OF THE COLD FRONT AND
COVER THE AREA FROM 29N-33N BETWEEN 60W-72W. FARTHER TO THE
SE...ANOTHER WEAKER SURFACE TROUGH EXTENDS FROM 22N62W TO
27N61W. SCATTERED SHOWERS ARE WITHIN 120 NM EITHER SIDE OF THE
TROUGH AXIS. THIS TROUGH IS SUPPORTED BY AN UPPER LEVEL LOW NEAR
25N59W. SCATTERED SHOWERS ARE ALSO N OF THE WINDWARD ISLANDS
FROM 18N-21N BETWEEN 60W-66W IN ASSOCIATION WITH THE UPPER LOW.
A 1012 MB SURFACE LOW IS CENTERED NEAR 16N46W WITH SCATTERED
SHOWERS AND ISOLATED TSTMS COVERING THE AREA NE OF THE LOW
CENTER FROM 15N-22N BETWEEN 37W-45W. ELSEWHERE ACROSS THE
ATLC...A BROAD SURFACE RIDGE DOMINATES ANCHORED BY A 1026 MB
HIGH NEAR 33N41W. IN THE UPPER LEVELS...AN UPPER LEVEL RIDGE IS
N OF 25N BETWEEN 34W-43W. AN UPPER LEVEL LOW DOMINATES THE NE
ATLC CENTERED NEAR 30N27W. MOIST SWLY UPPER LEVEL FLOW IS E OF
28W ACROSS THE ERN ATLC AND IS GENERATING POSSIBLE ISOLATED
SHOWERS FROM THE CAPE VERDE ISLANDS TO NE OF THE CANARY ISLANDS.

$$
HUFFMAN





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