Atlantic Tropical Weather Discussion

000
AXNT20 KNHC 132350
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SAT OCT 13 2012

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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2315 UTC.

...SPECIAL FEATURES...

TROPICAL STORM RAPHAEL IS CENTERED NEAR 17.9N 63.5W AT 14/0000 
UTC OR ABOUT 20 NM WSW OF ST. MARTIN...AND 75 NM E OF ST. CROIX. 
RAPHAEL IS MOVING N AT 10 KT. MINIMUM CENTRAL PRESSURE IS 1O04 
MB. MAXIMUM SUSTAINED WIND SPEED IS 45 KT WITH GUSTS TO 55 KT. 
SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS 
MIATCMAT2/WTNT22 KNHC. WATCHES AND WARNINGS HAVE BEEN PLACED 
OVER A GOOD PORTION OF THE EASTERN CARIBBEAN. THE SYSTEM IS 
SUPPORTING A LARGE AREA OF STRONG CONVECTION FROM 14N-19N 
BETWEEN 61W-64W IMPACTING MUCH OF THE LEEWARD ISLANDS. SCATTERED 
MODERATE/STRONG CONVECTION IS ELSEWHERE FROM 12N-24N BETWEEN 
57W-65W. HEAVY RAINFALL IS EXPECTED TO CONTINUE WITH FLOODING 
LIKELY ACROSS THE ISLANDS IMPACTED. 

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 18N33W TO 10N33W MOVING WEST NEAR 15 KT. 
THE WAVE LIES WITHIN A BROAD LOW-AMPLITUDE SURGE OF DEEP LAYER 
MOISTURE PRESENT IN TOTAL PRECIPITABLE WATER IMAGERY. THE LAST 
VISIBLE SATELLITE IMAGES OF THE DAY ALSO INDICATED THAT THERE 
WAS LOW-LEVEL CYCLONIC FLOW AROUND THE WAVE AXIS. DUE TO AN 
UPPER LEVEL TROUGH JUST WEST OF THE WAVE...CONVECTION IS BEING 
SHEARED TO THE EAST. SCATTERED MODERATE/STRONG CONVECTION IS 
FROM 6N-10N BETWEEN 30W-36W...AND FROM 10N-15N BETWEEN 30W-33W. 
MORE CONVECTION CONTINUES FARTHER E...BUT IS LIKELY MORE TIED TO 
THE UPPER TROUGH THAN THE WAVE. 

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

THE MONSOON TROUGH EXTENDS ACROSS W AFRICA TO THE COAST OF 
GUINEA-BISSAU AT 12N17W CONTINUING TO 10N22W. THE ITCZ BEGINS AT 
10N22W AND CONTINUES ALONG 10N30W 8N38W 8N44W. SCATTERED 
MODERATE/STRONG CONVECTION IS FROM 8N-11N BETWEEN 21W-30N...AND 
FROM 12N-16N BETWEEN 24W-30W. THIS ACTIVITY IS BEING ENHANCED BY 
AN UPPER LEVEL TROUGH TO THE WEST. SIMILAR ACTIVITY IS ALSO FROM 
8N-11N BETWEEN 44W-54W.   

...DISCUSSION...

GULF OF MEXICO...
FAIR WEATHER DOMINATES THE GULF OF MEXICO TONIGHT DUE TO DRY AIR 
ALOFT AROUND AN UPPER LEVEL RIDGE EXTENDING FROM CENTRAL MEXICO 
TO THE GREAT LAKES REGION. THE UPPER RIDGE SUPPORTS A SURFACE 
RIDGE ANCHORED BY A 1033 MB HIGH CENTERED JUST OFFSHORE OF 
DELAWARE. THIS PATTERN IS PROVIDING ANTI-CYCLONIC SURFACE FLOW 
ACROSS THE GULF WITH WIND SPEEDS RANGING FROM 15-20 KT WITH THE 
STRONGEST WINDS RESIDING IN THE SE GULF. THE RIDGE IS EXPECTED 
TO MOVE EASTWARD OVER THE NEXT 24 HOURS WITH SURFACE RIDGING 
REMAINING ACROSS THE GULF UNTIL A WEAK COLD FRONT MOVES INTO THE 
BASIN EARLY MONDAY FOLLOWED BY A STRONGER FRONT LATER IN THE 
WEEK. 

CARIBBEAN SEA...
TROPICAL STORM RAPHAEL CONTINUES TO IMPACT THE EASTERN CARIBBEAN 
BRINGING GUSTY WINDS AND HEAVY RAINFALL TO MUCH OF THE LEEWARD 
ISLANDS. SEE SPECIAL FEATURES ABOVE FOR MORE DETAILS. THE NW 
CARIBBEAN IS EXPERIENCING FAIR CONDITIONS DUE TO DRY AIR AND 
SUBSIDENCE ALOFT SINKING SOUTHWARD FROM THE GULF OF MEXICO. 
HOWEVER...A NARROW UPPER TROUGH EXTENDS FROM CENTRAL CUBA TO 
HONDURAS PROVIDING AN AREA OF DIFFLUENCE AND MOISTURE 
ALOFT...WHICH SUPPORTING A FEW SHOWERS/THUNDERSTORMS FROM 
HONDURAS AND NICARAGUA TO JAMAICA AND EASTERN CUBA. 
SHOWERS/THUNDERSTORMS ARE ALSO ACROSS COSTA RICA AND PANAMA 
ASSOCIATED WITH THE MONSOON TROUGH THAT EXTENDS FROM COSTA RICA 
TO NORTHERN COLOMBIA. THE CENTRAL CARIBBEAN IS ALSO EXPERIENCING 
FAIR WEATHER DUE TO MODERATE DRY AIR ALOFT AROUND THE WEST SIDE 
OF AN UPPER LEVEL RIDGE COVERING NORTHERN SOUTH AMERICA AND THE 
CENTRAL CARIBBEAN. AN UPPER LEVEL TROUGH IS STILL PROVIDING 
SHEAR ACROSS T.S. RAPHAEL IN THE EASTERN CARIBBEAN. RAPHAEL IS 
EXPECTING TO CONTINUE IMPACTING THE NE CARIBBEAN FOR AT LEAST 
THE NEXT 24 HOURS. 

ATLANTIC OCEAN...
A SURFACE TROUGH IS IN THE WEST ATLC ALONG 28N71W TO 
23N74W...WHICH IS THE REMNANTS OF TROPICAL DEPRESSION PATTY THAT 
DISSIPATED EARLIER TODAY. ISOLATED SHOWERS/THUNDERSTORMS REMAIN 
WITHIN 200 NM EITHER SIDE OF THE AXIS. AN ASCAT PASS FROM 
EARLIER TODAY ALSO INDICATES THAT STRONG N-NE WINDS UP TO 30 KT 
REMAIN TO THE NORTH OF THE TROUGH. ALOFT...AN UPPER LEVEL TROUGH 
IS ALONG 72W PROVIDING MOIST AND DIFFLUENT FLOW TO THE EAST OF 
THE AXIS SUPPORTING SHOWERS AND ISOLATED THUNDERSTORMS NORTH OF 
25N BETWEEN 60W-67W. AN UPPER LEVEL RIDGE IS FARTHER EAST ALONG 
56W DRAWING MOISTURE NORTH AND EASTWARD FROM TROPICAL STORM 
RAPHAEL IN THE CARIBBEAN. SHOWERS AND POSSIBLE THUNDERSTORMS ARE 
SOUTH OF 26N BETWEEN 57W-65W AND EXTEND INTO STRONGER ACTIVITY 
TIED TO THE STORM. SEE SPECIAL FEATURES FOR MORE DETAILS ON 
RAPHAEL. A LARGE UPPER LEVEL RIDGE DOMINATES THE MAJORITY OF THE 
NE ATLC SUPPORTING A SURFACE RIDGE ANCHORED BY A 1026 MB HIGH 
NEAR 34N35W. HOWEVER...A LARGE UPPER LEVEL LOW IS ACROSS THE 
TROPICAL ATLC CENTERED NEAR 23N33W IS SUPPORTING A SURFACE 
TROUGH ALONG 28N35W TO 20N39W. SCATTERED SHOWERS/POSSIBLE 
THUNDERSTORMS ARE EAST OF THE TROUGH FROM 20N-24N BETWEEN 
34W-38W. THE UPPER LOW/TROUGH IS ALSO ENHANCING CONVECTION NEAR 
THE ITCZ REGION. 

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

$$
WALTON