[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 201758
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
105 PM EST TUE DEC 20 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
1700 UTC.

...THE ITCZ/THE MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS INLAND OVER W AFRICA TO THE COAST OF
SRN SIERRA LEONE NEAR 7N13W CONTINUING TO 7N18W. THE ITCZ
CONTINUES FROM 7N18W ALONG 4N31W 4N49W. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS FROM 3N-6N BETWEEN
17W-28W...AND FROM 3N-5N BETWEEN 37W-48W.

...DISCUSSION...

GULF OF MEXICO...
SURFACE RIDGING DOMINATES THE MAJORITY OF THE GULF OF MEXICO
TODAY WITH AXIS EXTENDING FROM A 1027 MB HIGH IN THE W ATLC NEAR
31N71W. HOWEVER...A COLD FRONT IS JUST EMERGING OFF THE COAST OF
TEXAS AS OF 1500 UTC EXTENDING FROM SW LOUISIANA NEAR 30N94W
REMAINING PARALLEL TO THE COASTLINE TO NEAR 27N97W AND MOVING
INLAND OVER THE SRN TIP OF TEXAS AND NRN MEXICO TO NEAR 25W101W.
RADAR IMAGERY INDICATES A STRONG LINE OF SHOWERS/THUNDERSTORMS
ALONG THE FRONT AXIS WITH A FEW ISOLATED SHOWERS BOTH FARTHER
AHEAD AND BEHIND THE AXIS. NLY WINDS UP TO 20 KTS ARE ALSO
BEHIND THE FRONT WITH MOSTLY SE-S WINDS OF 15-20 KTS ACROSS THE
REMAINDER OF THE BASIN AROUND THE RIDGE. RADAR AND SATELLITE
IMAGERY ARE ALSO INDICATING A FEW OTHER AREAS OF ISOLATED
SHOWERS ACROSS THE BASIN INCLUDING PORTIONS OF THE CENTRAL GULF
BETWEEN 85W-89W. ALOFT...UPPER LEVEL RIDGING IS OVER THE ERN
HALF OF THE BASIN WHILE AN UPPER LEVEL TROUGH IS COVERING THE
CENTRAL CONUS TO THE NW CORNER SUPPORTING THE FRONTAL BOUNDARY.
THE FRONT IS EXPECTED TO SLOWLY MOVE EWD OVER THE NEXT 24 HOURS
BEFORE STALLING AND RETREATING BACK TO THE NW BEFORE A SECOND
FRONT MOVES OFF THE COAST ON THURSDAY.

CARIBBEAN SEA...
A DISSIPATING COLD FRONT IS LYING ACROSS THE NE CARIBBEAN
ISLANDS ALONG 19N BETWEEN 62W-73W PRODUCING ISOLATED SHOWERS
WITHIN 50 NM EITHER SIDE THE AXIS. THE FRONT IS EXPECTED TO
STALL AND CONTINUE DISSIPATING OVER THE NEXT 24 HOURS. THE
REMAINDER OF THE BASIN IS DOMINATED BY NE-E TRADEWIND FLOW OF
MAINLY 20 KTS WITH AREAS OF 25 KT WINDS N OF COLOMBIA. ISOLATED
SHOWERS ARE EMBEDDED WITHIN THE TRADEWIND FLOW BASIN-WIDE.
ENHANCED CONVECTION IN THE SW CARIBBEAN DUE TO THE MONSOON
TROUGH HAS DIMINISHED COMPARED TO THE PAST FEW DAYS...BUT AMPLE
MOISTURE REMAINS PRESENT. ALOFT...AN UPPER LEVEL RIDGE EXTENDS
FROM VENEZUELA TO CUBA AND UP THE ERN UNITED STATES SEABOARD.
PATCHES OF UPPER LEVEL MOISTURE ARE BEING DRAWN AROUND THE UPPER
RIDGE SUPPORTING A FEW HIGH CLOUDS. EXPECT STRONG TRADEWIND FLOW
TO REMAIN ACROSS MUCH OF THE BASIN AS HIGH PRESSURE OVER THE WRN
ATLC CONTINUES TO CREATE A STRONG PRESSURE GRADIENT.

ATLANTIC OCEAN...
SURFACE RIDGING AROUND A 1027 MB HIGH NEAR 31N71W IS PROVIDING
MOSTLY FAIR WEATHER ACROSS THE WRN ATLC. THE RIDGE IS SUPPORTED
BY AN UPPER LEVEL RIDGE WITH AXIS ALONG 76W. AN UPPER LEVEL
TROUGH TO THE E CONTINUES TO SUPPORT A LARGE COLD FRONT
IMPACTING THE CENTRAL ATLC ALONG 32N42W 24N49W 19N62W BECOMING
DISSIPATING TO 19N73W. ISOLATED SHOWERS ARE WITHIN 75 NM BEHIND
THE FRONT WITH AN AREA OF SCATTERED SHOWERS AHEAD OF THE FRONT N
OF 25N BETWEEN 37W-43W. TO THE S...A SURFACE TROUGH IS ALONG
14N53W TO 11N58W SUPPORTING SCATTERED SHOWERS/POSSIBLE
THUNDERSTORMS FROM 11N-13N BETWEEN 54W-63W. THESE SHOWERS MAY
DRIFT WWD AND IMPACT THE SRN WINDWARD ISLANDS. THE REMAINDER OF
THE BASIN IS INFLUENCED BY SURFACE RIDGING AROUND A 1036 MB HIGH
NE OF THE AZORES ISLANDS NEAR 40N22W PROVIDING GENERALLY FAIR
WEATHER ACROSS THE ERN ATLC. ALOFT...AN UPPER LEVEL RIDGE
CENTERED OVER THE AZORES ISLANDS IS SUPPORTING THE SURFACE
RIDGE. A CUT-OFF UPPER LEVEL LOW IS CENTERED TO THE S NEAR
23N26W CAUSING NO SIGNIFICANT WEATHER BESIDES A FEW UPPER LEVEL
CLOUDS NEAR THE AFRICAN COAST N OF THE ITCZ.


A SHORTWAVE UPPER TROUGH OVER THE NW ATLC IS SUPPORTING A COLD
FRONT ENTERING THE DISCUSSION AREA ALONG 32N54W 26N58W 22N67W
22N76W AND DISSIPATING TO CENTRAL CUBA. GALE FORCE WINDS ARE
NOTED N OF 29N BEHIND THE FRONT. DUE TO DRY AIR ALOFT...ISOLATED
SHOWERS ARE ONLY WITHIN 60 NM AHEAD OF THE AXIS WITH WIDESPREAD
STRATOCUMULUS CLOUDS BEHIND IT. A PRE-FRONTAL TROUGH IE E OF THE
FRONT ALONG 50W N OF 25N. POSSIBLE ISOLATED SHOWERS ARE ALONG
THE TROUGH AXIS. A SURFACE RIDGE IS BUILDING IN
BEHIND THE FRONT CURRENTLY ANCHORED AROUND A 1030 MB HIGH JUST
OFFSHORE OF NORTH CAROLINA. FARTHER S IN THE TROPICAL ATLC...A
SURFACE TROUGH IS ALONG 14N52W TO 9N56W. SCATTERED SHOWERS ARE
WITHIN 200 NM NW OF THE AXIS. THE REMAINDER OF THE ERN ATLC IS
UNDER THE INFLUENCE OF SURFACE RIDGING AROUND A 1034 MB HIGH
OVER THE AZORES ISLANDS. ALOFT...AN UPPER LEVEL RIDGE IS
CENTERED NEAR 34N25W SUPPORTING THE SURFACE RIDGE. A WEAK
SHORTWAVE UPPER TROUGH IS ALONG 33N42W TO 21N32W CAUSING LITTLE
SIGNIFICANT WEATHER. EXPECT THE FRONTAL SYSTEM IN THE CENTRAL
ATLC TO MOVE NE OVER THE NEXT SEVERAL DAYS.

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

$$
WALTON





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