[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 051749
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN OCT 05 2008

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 25W/26W S OF 18N MOVING W 10-15 KT. BROAD
LOW LEVEL CIRCULATION IS DISCERNIBLE ON SATELLITE IMAGERY AROUND
WAVE AXIS...WHICH COINCIDES WITH A MAXIMUM IN CIMSS WAVETRACK
DERIVED LOW LEVEL COUNTERCLOCKWISE CIRCULATION. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 210 NM W OF WAVE
AXIS N OF 10N...WITH ISOLATED MODERATE CONVECTION WITHIN 210 NM
W OF WAVE AXIS S OF 7N.

TROPICAL WAVE IS ALONG 55W/56W S OF 19N MOVING W NEAR 15 KT.
VISIBLE SATELLITE IMAGERY DEPICTS INVERTED-V SIGNATURE IN LOW
LEVEL CLOUD COVERAGE...WITH COUNTERCLOCKWISE CURVATURE IN
OBSERVED SURFACE WIND FIELD. ISOLATED SHOWERS ARE OCCURRING
WITHIN 90 NM EITHER SIDE OF WAVE AXIS N OF 12N.

TROPICAL WAVE IS ALONG 66W/67W S OF 19N MOVING W 10-15 KT. WAVE
STRUCTURE IS GENERALLY ILL-DEFINED FROM SATELLITE IMAGERY...
THOUGH COUNTERCLOCKWISE CURVATURE IS NOTED IN OBSERVED SURFACE
WIND FIELD OVER E CARIBBEAN REGION NEAR WAVE AXIS. ISOLATED
SHOWERS ARE WITHIN 150 NM E OF WAVE AXIS S OF 13N.

...THE ITCZ...
THE ITCZ AXIS IS ANALYZED ALONG 7N12W 8N23W 9N40W 12N54W 12N65W
ACROSS THE S CARIBBEAN INTO THE E PACIFIC REGION NEAR 11N86W.
ISOLATED MODERATE CONVECTION IS FROM 6N-13N BETWEEN 34W-40W.
SCATTERED MODERATE CONVECTION IS FROM 9N-15N BETWEEN 42W-47W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS OVER THE
S CARIBBEAN FROM 10N-14N BETWEEN 72W-83W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER TROUGH OVER THE E CONUS AND A SECONDARY UPPER TROUGH
OVER MEXICO EXTEND INTO THE GULF. AS A RESULT...SOUTHWESTERLY
FLOW ALOFT COVERS MUCH OF THE GULF...WITH MOISTURE STREAMING
THROUGH THE FLOW OVER THE GULF SE OF A LINE FROM 27N85W TO
20N97W. ALSO TO THE SE OF THIS LINE...A SURFACE TROUGH EXTENDS
FROM 23N88W TO A 1012 MB SURFACE LOW OVER THE YUCATAN PENINSULA
NEAR 19N89W...AND ANOTHER SURFACE TROUGH EXTENDS FROM NEAR THE
FLORIDA KEYS NEAR 25N82W TO THE S FLORIDA PENINSULA NEAR 25N80W.
WEAKLY CONVERGENT FLOW INTO THESE FEATURES...COMBINED WITH
MOISTURE AND ATMOSPHERIC LIFT IN SW FLOW ALOFT...IS RESULTING IN
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS OVER THE GULF S OF
26N BETWEEN 81W-88W. ISOLATED SHOWERS ARE OCCURRING OVER THE BAY
OF CAMPECHE IN RESPONSE TO LOW LEVEL SUPPORT FROM THE SURFACE
LOW OVER THE YUCATAN PENINSULA. DRY CONDITIONS COVER MUCH OF THE
GULF NW OF A LINE FROM 27N85W TO 20N97W.

CARIBBEAN SEA...
AN UPPER RIDGE EXTENDS FROM W CUBA TO THE GULF OF HONDURAS...
WITH DEEP MOISTURE CIRCULATING AROUND THE RIDGE. ALSO...A
1012 MB SURFACE LOW IS OVER THE YUCATAN PENINSULA NEAR
19N89W...WITH A SURFACE TROUGH EXTENDING FROM THE LOW INTO THE
GULF OF MEXICO NEAR 23N88W. THESE FEATURES CONTINUE TO RESULT IN
SCATTERED MODERATE CONVECTION OVER THE NW CARIBBEAN N OF 17N AND
W OF 82W...AFFECTING THE YUCATAN PENINSULA AND BELIZE. TO THE
E...AN UPPER TROUGH EXTENDS NORTHWARD FROM PANAMA TO HAITI. DEEP
TROPICAL MOISTURE AND WEAKLY UNSTABLE AIR WITHIN THE
TROUGH...COMBINED WITH WEAK LOW LEVEL CONVERGENCE NEAR THE ITCZ
AXIS...ARE RESULTING IN SCATTERED MODERATE CONVECTION FROM
9N-14N BETWEEN 72W-81W...AFFECTING THE SW CARIBBEAN. OVER THE E
CARIBBEAN...DRIER AIR IS PRESENT UNDER WEAK A WEAK RIDGE
ALOFT...WITH ISOLATED SHOWERS S OF 16N AND E OF 69W BEING
SUPPORTED BY THE ITCZ.

ATLANTIC OCEAN...
AN UPPER TROUGH OVER THE E CONUS CONTINUES TO SUPPORT MOIST
SOUTHWESTERLY FLOW ALOFT OVER THE SW ATLC...WHERE A WEAKENING
STATIONARY SURFACE FRONT EXTENDS FROM 23N71W TO 28N77W AND A
SURFACE TROUGH EXTENDS FROM 28N77W TO THE S FLORIDA PENINSULA
NEAR 25N80W. THE COMBINATION OF THESE FEATURES CONTINUES
RESULTING IN ISOLATED SHOWERS AND THUNDERSTORMS WITHIN 150 NM
EITHER SIDE OF THE WEAKENING STATIONARY SURFACE FRONT AND THE
SURFACE TROUGH. AN UPPER HIGH NEAR 29N68W AND ITS ASSOCIATED
UPPER RIDGE ARE BRINGING DRY AND STABLE CONDITIONS TO THE W ATLC
N OF 21N BETWEEN 59W-74W. A DEEP UPPER LOW SPINNING OVER THE
CENTRAL ATLC NEAR 22N57W IS SUPPORTING A SURFACE TROUGH THAT
EXTENDS FROM 27N55W TO NEAR 21N56W. THIS SURFACE TROUGH
CONTINUES TO MOVE WESTWARD ON THE SOUTHERN PERIPHERY OF THE
SURFACE RIDGE OVER THE CENTRAL ATLC ANCHORED BY A 1025 MB HIGH
NEAR 34N38W. THE SURFACE TROUGH IS SUPPORTING SCATTERED MODERATE
CONVECTION WITHIN 180 NM E OF THE TROUGH AXIS S OF 22N AND
ISOLATED MODERATE CONVECTION WITHIN 150 NM E OF THE TROUGH AXIS
N OF 25N. OVER THE NE ATLC...AN UPPER TROUGH IS N OF 19N BETWEEN
THE W AFRICAN COAST AND 32W. UPPER SUPPORT FROM AN UPPER LEVEL
WIND SPEED MAXIMUM E OF THE TROUGH AXIS IS GENERATING SCATTERED
MODERATE CONVECTION FROM 20N-24N BETWEEN 18W-23W. THE TYPICAL
E/W UPPER RIDGE AXIS EXTENDS ACROSS THE TROPICAL ATLC ALONG 12N
BETWEEN W AFRICA AND 51W.

$$
COHEN



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