[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 241755
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SAT SEP 24 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 17.8N 56.0W AT 24/1500
UTC OR ABOUT 335 NM E OF THE LEEWARD ISLANDS MOVING NW AT 11 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1006 MB. MAXIMUM SUSTAINED
WIND SPEED IS 45 KT WITH GUSTS TO 55 KT. PLEASE SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC
FOR MORE DETAILS. CONVECTION HAS BEGUN TO REDEVELOP NEAR THE
CENTER OF OPHELIA. CURRENTLY NUMEROUS STRONG CONVECTION IS FROM
16N-17N BETWEEN 52W-54W...AND FROM 17N-21N BETWEEN 52W-56W.
SCATTERED MODERATE/STRONG CONVECTION IS FROM 12N-14N BETWEEN
53W-56W...AND FROM 16N-21N BETWEEN 56W-58W.

TROPICAL DEPRESSION SEVENTEEN IS CENTERED NEAR 11.0N 26.7W AT
24/1500 UTC...OR ABOUT 265 NM SSW OF THE SOUTHERNMOST CAPE VERDE
ISLANDS MOVING WNW NEAR 14 KT. ESTIMATED MINIMUM CENTRAL
PRESSURE IS 1006 MB. MAXIMUM SUSTAINED WIND SPEED IS 30 KT WITH
GUSTS TO 40 KT. PLEASE SEE LATEST NHC FORECAST/ADVISORY UNDER
AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS.
SCATTERED MODERATE/STRONG CONVECTION IS AROUND THE WRN
SEMI-CIRCLE FROM 8N-13N BETWEEN 26W-29W.

A SURFACE TROUGH E OF THE FLORIDA PENINSULA ALONG 30N78W TO
25N78W IS PRODUCING A LARGE AREA OF SHOWERS/THUNDERSTORMS ACROSS
THE BAHAMAS. NUMEROUS SHOWERS/THUNDERSTORMS ARE FROM 21N-25N
BETWEEN 75W-78W. SCATTERED SHOWERS/THUNDERSTORMS ARE N OF 25N
BETWEEN 76W-79W. THIS AREA HAS BECOME A LITTLE BETTER ORGANIZED
OVER THE PAST SEVERAL HOURS AND SOME ADDITIONAL ORGANIZATION IS
POSSIBLE OVER THE NEXT DAY OR SO AS THE SYSTEM MOVES NWD.

...TROPICAL WAVES...

TROPICAL WAVE IS IN THE CENTRAL ATLC ALONG 20N38W TO 12N39W
MOVING W 10-15 KT. VISIBLE SATELLITE IMAGERY ALONG WITH AN ASCAT
SCATTEROMETER FROM 1240 UTC SHOWS CYCLONIC SURFACE FLOW AROUND
THE WAVE AXIS. TOTAL PRECIPITABLE WATER IMAGERY ALSO INDICATES
THE WAVE LIES AHEAD OF A SURGE OF DEEP LAYER MOISTURE. CURRENTLY
NO DEEP CONVECTION ACCOMPANIES THE WAVE.

...ITCZ/MONSOON TROUGH...

DUE TO THE CIRCULATION OF T.D. SEVENTEEN...THE MONSOON TROUGH
HAS BROKEN DOWN WITH ONLY PORTIONS OVER AFRICA REMAINING. AS
T.D. SEVENTEEN MOVES TOWARDS THE WEST...THE MONSOON TROUGH WILL
BUILD BACK IN BEHIND IT.

...DISCUSSION...

GULF OF MEXICO...
AS OF 1500 UTC...A WEAK STATIONARY FRONT EXTENDS ACROSS THE NRN
GULF OF MEXICO FROM N CENTRAL FLORIDA NEAR TALLAHASSEE TO S OF
LOUISIANA ALONG 31N84W TO 29N91W. THE FRONT IS SUPPORTED BY A
LONGWAVE UPPER LEVEL TROUGH THAT COVERS THE ERN CONUS. DRY AIR
ALOFT IS SINKING DOWN INTO THE AREA WHICH IS LIMITING SHOWER
ACTIVITY ALONG THE FRONT. A SURFACE TROUGH EXTENDS S OF THE
FRONTAL BOUNDARY ALONG 27N85W TO 23N91W SUPPORTING ISOLATED
SHOWERS WITHIN 100 NM OF THE AXIS. A FEW ISOLATED SHOWERS HAVE
ALSO FORMED OVER SW FLORIDA AND ARE MOVING EWD. WEAK UPPER
RIDGING COVERS THE SE GULF EXTENDING FROM THE YUCATAN PENINSULA.
EXPECT THE FRONTAL BOUNDARY TO REMAIN STATIONARY AND BEGIN TO
WEAKEN. THE UPPER LEVEL TROUGH WILL ALSO REMAIN SOMEWHAT
STATIONARY ACROSS THE ERN CONUS KEEPING DRY AIR ACROSS THE NW
GULF WHICH WILL SUPPORT FAIR CONDITIONS.

CARIBBEAN SEA...
UPPER LEVEL RIDGING COVERS THE WRN CARIBBEAN AROUND AN AXIS OVER
THE YUCATAN PENINSULA AND A SECOND AXIS OVER THE SW CARIBBEAN.
AN UPPER LEVEL TROUGH COVERS THE ERN CARIBBEAN ACCOMPANIED BY
DRY AIR. TOTAL PRECIPITABLE WATER IMAGERY INDICATES AN AREA OF
MOISTURE OVER THE WRN CARIBBEAN WHICH IS HELPING SUPPORT
SCATTERED SHOWERS/THUNDERSTORMS FROM 12N-18N BETWEEN 78W-85W.
SHOWERS/THUNDERSTORMS ARE ALSO S OF 12N INFLUENCED BY THE
MONSOON TROUGH THAT EXTENDS FROM SRN COSTA RICA TO NRN COLOMBIA.
THE ERN CARIBBEAN IS UNDER MOSTLY FAIR CONDITIONS DUE TO THE
AFOREMENTIONED DRY ALOFT ALONG WITH 15-20 KT ELY TRADEWIND FLOW.
TROPICAL STORM OPHELIA IS CURRENTLY E OF THE NRN LEEWARD ISLANDS
AND IS EXPECTED TO MOVE N OF THE CARIBBEAN. SOME OF THE MOISTURE
TO THE S OF THE SYSTEM MAY STILL MAKE ITS WAY INTO THE ERN
CARIBBEAN.

ATLANTIC OCEAN...
A SURFACE TROUGH E OF THE FLORIDA PENINSULA IS PRODUCING A LARGE
AREA OF SHOWERS/THUNDERSTORMS ACROSS THE SW N ATLC INCLUDING
MUCH OF THE BAHAMAS. SEE SPECIAL FEATURES ABOVE FOR MORE
DETAILS. ALOFT...AN UPPER LEVEL TROUGH OVER THE ERN CONUS
EXTENDS SLIGHTLY OVER THE WRN ATLC WITH AN UPPER LEVEL RIDGE TO
THE E CENTERED NEAR 34N66W. THIS UPPER RIDGE IS SUPPORTING A
SURFACE RIDGE AROUND A 1026 MB HIGH NEAR 33N61W SUPPORTING FAIR
WEATHER. AN UPPER LEVEL LOW IS TO THE S NEAR 22N67W. THIS UPPER
LEVEL LOW/TROUGH CONTINUES TO HELP SHEAR T.S. OPHELIA. ANOTHER
LONGWAVE UPPER TROUGH COVERS THE ERN ATLC SUPPORTING A COLD
FRONT THAT CLIPS THE AREA ALONG 32N32W TO 30N38W SUPPORTING
ISOLATED SHOWERS WITHIN 100 NM OF THE AXIS. A WEAK 1021 MB HIGH
IS E OF THE FRONT NEAR THE MADEIRA ISLANDS PROVIDING FAIR
WEATHER ACROSS THE SE ATLC. A BROAD UPPER LEVEL RIDGE COVERS THE
TROPICAL ATLC CENTERED NEAR 16N34W. T.S. OPHELIA WILL CONTINUE
TO MOVE NW WHILE T.D. SEVENTEEN WILL MOVE WWD.

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

$$
WALTON







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