[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 181755
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN SEP 18 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
1745 UTC.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST OF GUINEA
BISSAU NEAR 12N16W TO A 1011 MB LOW NEAR 11N24W TO A SECOND 1009
MB LOW NEAR 11N35W ENDING NEAR 8N47W. THE MONSOON TROUGH HAS
BECOME THE DOMINANT FEATURE ACROSS THE TROPICAL ATLC OVER THE
PAST 6-8 HOURS...LEADING TO A WEAKENING OF THE INTER-TROPICAL
CONVERGENCE ZONE. THE LARGE AND STRETCHED OUT MONSOON GYRE IS
PRODUCING WIDELY SCATTERED MODERATE TO ISOLATED STRONG
CONVECTION FROM 4N-14N E OF 47W.

...DISCUSSION...

GULF OF MEXICO...
SATELLITE VISIBLE IMAGERY SHOWS MOSTLY CLEAR SKIES WITH A FEW
ISOLATED WEAK SHOWERS MOVING ALONG WITH THE LIGHT ANTICYCLONIC
FLOW PRESENT ACROSS THE BASIN. WATER VAPOR IMAGERY SHOWS AN
UPPER LEVEL TROUGH/SHORT WAVE MOVING EASTWARD ACROSS SOUTHERN
TEXAS...SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
MOVING ALONG THE TEXAS COAST UP TO 70 NM OFFSHORE. COMPUTER
MODELS SUGGEST SIMILAR ACTIVITY LINGERING OVER THE FAR NW BASIN
OVER THE NEXT 24 HOURS. DOPPLER RADAR IMAGERY INDICATES A
CLUSTER OF SHOWERS AND ISOLATED THUNDERSTORMS MOVING WESTWARD
ACROSS THE FLORIDA STRAITS E OF 83W. AN INCREASE IN CONVECTION
OVER THIS REGION IS EXPECTED AS A SURFACE TROUGH CROSSES THE
FLORIDA PENINSULA INTO THE EASTERN GULF THIS AFTERNOON.

CARIBBEAN SEA...
MODERATE TO HIGH SURFACE MOISTURE VALUES ARE NOTED ON TOTAL
PRECIPITABLE WATER IMAGERY W OF 80W. WHILE SCATTERED SHOWERS
ROAM THIS AREA...STRONGER ACTIVITY FOCUSES OVER THE YUCATAN
CHANNEL AND THE COASTAL WATERS NEAR EASTERN HONDURAS...
NICARAGUA...COSTA RICA...PANAMA...AND COLOMBIA UP TO 100 NM
OFFSHORE W OF 75W. MOST OF THE ACTIVITY S OF 12N W OF 75W IS
ALSO ENHANCED BY THE MONSOON TROUGH ANALYZED OVER THE FAR SW
BASIN EXTENDING ACROSS COSTA RICA INTO NORTHERN COLOMBIA. THIS
AREA OF CONVECTION IS MOVING INLAND OVER CENTRAL AMERICA...WITH
THE ACTIVITY EXPECTED TO CONTINUE TO IMPACT THE REGION OVER THE
NEXT 24 HOURS. WATER VAPOR IMAGERY SHOWS A BROAD UPPER LEVEL
CYCLONIC CIRCULATION OVER PUERTO RICO. WITH PLENTY OF LOW LEVEL
MOISTURE IN ITS SURROUNDINGS...THIS FEATURE IS PROVIDING MID TO
UPPER LEVEL LIFT AND INSTABILITY TO GENERATE AN AREA OF
SCATTERED MODERATE TO STRONG CONVECTION AFFECTING THE FAR NE
CARIBBEAN N OF 13N E OF 68W INCLUDING THE LESSER ANTILLES. THIS
SYSTEM IS EXPECTED TO DRIFT WWD WHICH SHOULD INCREASE THE
SHOWER ACTIVITY OVER THE CENTRAL PORTION OF THE BASIN. THE
REMAINDER OF THE BASIN REMAINS UNDER FAIR WEATHER CONDITIONS.

ATLANTIC OCEAN...
AN UPPER LEVEL TROUGH MOVES OFF THE EASTERN CONUS SEABOARD THIS
AFTERNOON...SUPPORTING A FRONTAL BOUNDARY THAT ENTERS OUR
DISCUSSION AREA AS STATIONARY NEAR 32N76W EXTENDING SW TO THE
FLORIDA COAST NEAR DAYTONA BEACH. LOW-LEVEL CONVERGENCE AND
UPPER DIVERGENCE IN THE VICINITY OF THE FRONT IS GENERATING
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WITHIN 30 NM ON
EITHER SIDE OF THE FRONT. TO THE S OF THIS BOUNDARY...A SURFACE
TROUGH MOVES ACROSS THE NORTHERN BAHAMAS ANALYZED FROM 29N77W TO
23N80W. THE ACTIVITY ASSOCIATED TO THIS SYSTEM IS AFFECTING THE
COASTAL WATERS OF CUBA S OF 25N W OF 77W...AND SOME OF THIS
ACTIVITY IS MOVING WESTWARD INTO THE FLORIDA STRAITS. A BROAD
UPPER LEVEL CYCLONIC CIRCULATION IS SPINNING OVER THE ISLAND OF
PUERTO RICO. WITH PLENTY OF LOW LEVEL MOISTURE IN ITS
SURROUNDINGS...THIS FEATURE IS PROVIDING MID TO UPPER LEVEL LIFT
AND INSTABILITY TO GENERATE AN AREA OF SCATTERED MODERATE TO
STRONG CONVECTION S OF 26N BETWEEN 60W-68W. FARTHER E...A 1010
MB LOW/TROUGH SYSTEM IS CENTERED NEAR 17N45W PRODUCING AN AREA
OF DISORGANIZED SHOWERS AND THUNDERSTORMS FROM 15N-20N BETWEEN
40W-45W. THIS SYSTEM WILL CONTINUE TO SLOWLY MOVE WESTWARD OVER
THE NEXT 24 HOURS WITH VERY LOW CHANCES TO BECOME A TROPICAL
STORM. TO THE N OF THIS LOW PRESSURE SYSTEM...AN UPPER LEVEL LOW
CENTERED SW OF THE AZORES SUPPORTS A WEAK LOW PRESSURE SYSTEM
AND ASSOCIATED TROUGH WITH A NARROW LINE OF ISOLATED SHOWERS
EXTENDING ALONG THE BOUNDARY FROM 32N37W TO 27N40W TO 26N45W.
THE REMAINDER OF THE CENTRAL AND EASTERN ATLC IS UNDER THE
INFLUENCE OF A WEAK BROAD SURFACE RIDGE N OF THE AREA.

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

$$

GARCIA



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