[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 281753
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT WED SEP 28 2011

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...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL
ANALYSIS.

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

...SPECIAL FEATURES...

TROPICAL STORM OPHELIA IS CENTERED NEAR 18.7N 59.9W AT 28/1500
UTC OR ABOUT 185 NM E OF THE NORTHERN LEEWARD ISLANDS MOVING
N-NW AT 3 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1002 MB.
MAXIMUM SUSTAINED WIND SPEED IS 45 KT WITH GUSTS TO 55 KT.
SCATTERED MODERATE CONVECTION IS FROM 15N-21N BETWEEN 57W-60W
CONTINUING TO BE SHEARED TO THE EAST DUE TO AN UPPER LEVEL
TROUGH AXIS ALONG 63W. SEE LATEST NHC FORECAST/ADVISORY UNDER
AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS.

TROPICAL STORM PHILIPPE IS CENTERED NEAR 16.4N 38.8W AT 28/1500
UTC OR ABOUT 850 NM W OF THE CAPE VERDE ISLANDS MOVING W-NW AT
10 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB. MAXIMUM
SUSTAINED WIND SPEED IS 35 KT WITH GUSTS TO 45 KT. SCATTERED
MODERATE CONVECTION IS SHEARED TO THE NORTH OF THE CENTER OF
PHILIPPE AND IS OCCURRING FROM 16N-20N BETWEEN 35W-39W. SEE
LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/
WTNT22 KNHC FOR MORE DETAILS.

...TROPICAL WAVES...

TROPICAL WAVE IS ANALYZED FROM 04N29W TO 11N28W MOVING W AT
10-15 KT. THIS RELATIVELY LOW-LATITUDE WAVE CONTINUES TO EXHIBIT
CYCLONIC TURNING OF THE LOW-LEVEL CLOUD FIELD IN THE VICINITY OF
THE WAVE AXIS BETWEEN 25W-32W. NO SIGNIFICANT DEEP CONVECTION IS
OBSERVED ON VISIBLE SATELLITE IMAGERY AT THIS TIME.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 14N17W TO
08N21W. WIDELY SCATTERED MODERATE CONVECTION IS WITHIN 90 NM
EITHER SIDE OF A LINE FROM 08N16W TO 04N22W.

...DISCUSSION...

GULF OF MEXICO...
UPPER LEVEL WESTERLY FLOW DOMINATES ACROSS THE GULF THIS
AFTERNOON BETWEEN AN UPPER LEVEL LOW CENTERED OVER THE GREAT
LAKES REGION AND AN ANTICYCLONIC CIRCULATION CENTERED OVER
SOUTHERN MEXICO NEAR 17N95W. WATER VAPOR IMAGERY INDICATES A
MODERATELY DRY AIRMASS IS IN PLACE ACROSS MUCH OF THE GULF. AT
THE SURFACE...A 1015 MB HIGH IS CENTERED IN THE CENTRAL GULF
NEAR 27N88W. A WEAKNESS WITHIN THE RIDGE IS APPARENT WITHIN THE
PRESSURE ANALYSIS OVER THE WEST-CENTRAL AND SW GULF WHERE WIDELY
SCATTERED SHOWERS AND ISOLATED TSTMS ARE OCCURRING S OF 25N W OF
94W. THIS ACTIVITY IS LIKELY ENHANCED DUE TO AN UPPER LEVEL
DIFFLUENT ENVIRONMENT ON THE NORTHERN PERIPHERY OF THE UPPER
LEVEL ANTICYCLONE OVER SOUTHERN MEXICO. ALSO OF NOTE...AN AREA
OF SCATTERED SHOWERS AND TSTMS IS OCCURRING OVER SOUTHERN
ALABAMA AND THE FLORIDA PANHANDLE...INCLUDING THE ADJACENT
COASTAL WATERS...N OF 29N BETWEEN 85W-89W. THE REMAINDER OF THE
GULF IS EXPERIENCING CLEAR SKIES AND FAIR WEATHER CONDITIONS DUE
TO THE SURFACE HIGH AND IS FORECAST TO REMAIN QUASI-STATIONARY
OVER THE CENTRAL GULF THROUGH THURSDAY.

CARIBBEAN SEA...
AN UPPER LEVEL ANTICYCLONIC CIRCULATION IS CENTERED OVER
SOUTHERN MEXICO NEAR 17N95W AND IS PROVIDING MUCH OF THE WESTERN
AND CENTRAL CARIBBEAN W OF 65W WITH NORTHWEST TO NORTHERLY FLOW
ALOFT. THIS DRY AND GENERALLY SUBSIDENT AIR IS MAINTAINING
MOSTLY FAIR WEATHER CONDITIONS AND CLEAR SKIES...HOWEVER...GIVEN
AN UPPER LEVEL DIFFLUENT ENVIRONMENT AND AREAS OF TRADEWIND
CONVERGENCE...ISOLATED SHOWERS ARE OCCURRING FROM 15N-18N
BETWEEN 71W-77W. ANOTHER AREA OF ISOLATED SHOWERS AND TSTMS IS
OCCURRING OFF THE COAST OF NICARAGUA FROM 11N-15N W OF 82W. THE
REMAINDER OF THE EASTERN CARIBBEAN E OF 65W FALLS UNDER THE
INFLUENCE OF TROPICAL STORM OPHELIA WHICH CONTINUES TO PROVIDE
SW TO W SURFACE WINDS ACROSS THE LESSER ANTILLES AND A FEW
ISOLATED SHOWERS AND TSTMS N OF 14N E OF 64W.

ATLANTIC OCEAN...
UPPER LEVEL DIFFLUENT FLOW IS NOTED W OF 70W ON WATER VAPOR
IMAGERY BETWEEN AN UPPER LEVEL LOW CENTERED OVER THE GREAT LAKES
REGION AND AN UPPER LEVEL ANTICYCLONIC CIRCULATION CENTERED OVER
SOUTHERN MEXICO. SOUTHWESTERLY UPPER LEVEL FLOW BETWEEN THESE
TWO FEATURES AND A SURFACE TROUGH ANALYZED FROM 24N80W TO 31N79W
IS PROVIDING FOCUS FOR SCATTERED SHOWERS AND ISOLATED TSTMS N OF
30N BETWEEN 71W-78W...WITHIN 90 NM EITHER SIDE OF THE SURFACE
TROUGH BOUNDARY...AND FROM 20N-25N BETWEEN 72W-78W...INCLUDING
THE CENTRAL AND SE BAHAMAS. EAST OF 70W...AN UPPER LEVEL TROUGH
AXIS EXTENDS ALONG 63W AND CONTINUES TO ADVECT MIDDLE TO UPPER
LEVEL MOISTURE ASSOCIATED WITH CONVECTIVE DEBRIS FROM TROPICAL
STORM OPHELIA NORTHWARD TO 29N. OPHELIA REMAINS UNDER A SHEARED
ENVIRONMENT DUE TO THE UPPER LEVEL TROUGH AND WIDELY SCATTERED
SHOWERS ARE OCCURRING OUTSIDE OF THE INFLUENCE OF OPHELIA FROM
21N-29N BETWEEN 55W-65W AS THE MOISTURE AND CLOUDINESS FANS N-NE.
NEARLY THE SAME SYNOPTIC SETUP IS PLAGUING TROPICAL STORM
PHILIPPE AS AN UPPER LEVEL LOW IS CENTERED TO THE WEST OF
PHILIPPE NEAR 18N45W. NUMEROUS SHOWERS AND SCATTERED TSTMS ARE
OCCURRING FROM 16N-20N BETWEEN 35W-39W. THE CENTRAL ATLC FALLS
WITHIN A WEAKNESS OF THE SUBTROPICAL RIDGE WITH A SURFACE TROUGH
ANALYZED FROM 32N37W TO 26N50W AHEAD OF A COLD FRONT DRAPED
NORTH OF THE DISCUSSION AREA ALONG 34N BETWEEN 40W-55W. ISOLATED
SHOWERS ARE OCCURRING WITHIN 60 NM EITHER SIDE OF THE SURFACE
TROUGH. THE REMAINDER OF THE EASTERN ATLC IS UNDER THE INFLUENCE
OF A SURFACE RIDGE ANCHORED BY A 1021 MB HIGH CENTERED SW OF THE
MADEIRA ISLANDS NEAR 32N18W.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

$$
HUFFMAN




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