[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 200551
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT TUE SEP 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0515 UTC.

...SPECIAL FEATURES...

A 1008 MB LOW IS EMBEDDED ALONG THE MONSOON TROUGH AXIS NEAR
11N37W MOVING W AT 5-10 KT. TOTAL PRECIPITABLE WATER IMAGERY
INDICATES THAT LOW-LEVEL MOISTURE IS MAXIMIZED FROM 07N-15N
BETWEEN 34W-43W. SCATTERED MODERATE AND ISOLATED STRONG
CONVECTION IS FROM 07N-15N BETWEEN 33W-42W. ENVIRONMENTAL
CONDITIONS REMAIN FAVORABLE FOR THE DEVELOPMENT OF A TROPICAL
DEPRESSION DURING THE NEXT COUPLE OF DAYS.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 19N16W TO
10N26W TO THE SPECIAL FEATURES 1008 MB LOW NEAR 11N37W TO
12N44W. WIDELY SCATTERED MODERATE CONVECTION IS FROM 04N-11N
BETWEEN 16W-29W...AND FROM 07N-10N BETWEEN 43W-49W.

...DISCUSSION...

GULF OF MEXICO...
WATER VAPOR IMAGERY INDICATES AN UPPER LEVEL SHORTWAVE TROUGH IS
PROGRESSING ACROSS THE MIDDLE AND LOWER MISSISSIPPI RIVER VALLEY
THIS EVENING WITH MOSTLY SOUTHWESTERLY FLOW ALOFT ACROSS MUCH OF
THE NORTHERN GULF WATERS. THIS TROUGH SUPPORTS A COLD FRONT
REMAINING NORTH OF THE GULF COAST ACROSS EASTERN TEXAS AND NW
LOUISIANA HOWEVER...A PRE-FRONTAL TROUGH EXTENDS FROM SE
LOUISIANA NEAR 30N91W TO 27N92W. LOW-LEVEL MOISTURE CONVERGENCE
IN THE VICINITY OF THE TROUGH ALONG WITH MIDDLE TO UPPER LEVEL
DIFFLUENCE IS GENERATING AN AREA OF ISOLATED SHOWERS AND TSTMS
WITHIN 90 NM EAST OF THE BOUNDARY...WITH DOPPLER RADAR IMAGERY
INDICATING THE STRONGEST CONCENTRATION OF ACTIVITY OVER MOBILE
BAY. SE OF THE PROGRESSIVE TROUGHING...AN UPPER LEVEL RIDGE AXIS
EXTENDS FROM THE SW GULF WATERS NE OVER THE FLORIDA PENINSULA
AND INTO THE SW NORTH ATLC. CONVECTIVE DEBRIS MOISTURE CONTINUES
SPILLING OVER THE CREST OF THE RIDGE WITH MOST MOISTURE LEFTOVER
FROM PRIOR AFTERNOON CONVECTION ACROSS THE FLORIDA PENINSULA.
WHILE EASTERLY FLOW PREVAILS ACROSS THE EASTERN GULF...
LOW-TOPPED ISOLATED SHOWERS ARE OCCURRING S OF 26N E OF 84W...
INCLUDING THE STRAITS OF FLORIDA.

CARIBBEAN SEA...
AN UPPER LEVEL SHORTWAVE TROUGH EXTENDS INTO THE WESTERN
CARIBBEAN FROM THE SW NORTH ATLC WITH AXIS FROM 26N72W TO
16N84W. THIS IS PROVIDING MUCH OF THE CARIBBEAN SEA WITH NORTH
TO GENERALLY WESTERLY UPPER LEVEL FLOW. WATER VAPOR IMAGERY
INDICATES MUCH OF THIS FLOW IS MODERATELY DRY ALOFT WITH VERY
FEW SHOWERS OCCURRING THIS EVENING S OF A LINE FROM THE YUCATAN
CHANNEL NEAR 22N86W TO 12N71W. NORTH OF THIS LINE HOWEVER...A
SURFACE TROUGH IS ANALYZED FROM WESTERN CUBA NEAR 23N81W TO
SOUTH OF JAMAICA NEAR 16N77W. ISOLATED SHOWERS AND TSTMS ARE
PRIMARILY OCCURRING NORTH OF THIS BOUNDARY WHERE LOW-LEVEL
MOISTURE CONVERGENCE IS MAXIMIZED. THIS CONVECTIVE ACTIVITY IS
PRIMARILY SOUTH OF CUBA AND N OF 16N BETWEEN 70W-83W. FARTHER
EAST...CONTINUED UPPER LEVEL TROUGHING OVER THE SW NORTH ATLC
EXTENDS SOUTHWARD INTO THE NE CARIBBEAN AND IS PROVIDING FOR THE
ADVECTION OF TROPICAL MOISTURE NORTHWARD ACROSS HISPANIOLA...
PUERTO RICO...AND THE LEEWARD ISLAND THIS EVENING. MOST OF THE
STRONGEST CONVECTIVE ACTIVITY HAS MOVED NE OF PUERTO RICO OVER
THE PAST 6 HOURS...HOWEVER...ISOLATED SHOWERS ARE OCCURRING N OF
13N E OF 68W. THE UPPER LEVEL TROUGHING AND SUBSEQUENT UPPER
LEVEL DIFFLUENT FLOW EAST OF THE TROUGH AXIS IS FORECAST TO
REMAIN IN PLACE ACROSS THE WESTERN CARIBBEAN THROUGH THURSDAY
MORNING...WITH THE INCREASED POSSIBILITY OF WIDELY SCATTERED
SHOWERS AND ISOLATED TSTMS OVER HISPANIOLA AND PUERTO RICO
THROUGH THE REMAINDER OF THE WEEK.

ATLANTIC OCEAN...
AN UPPER LEVEL RIDGE AXIS EXTENDS FROM THE EASTERN GULF OF
MEXICO OVER THE FLORIDA PENINSULA INTO THE SW NORTH ATLC TO
BEYOND 32N77W. EASTERLY LOW-LEVEL FLOW HOWEVER STILL REMAINS
CONVERGENT OVER THE FAR W ATLC WITH ISOLATED SHOWERS OCCURRING N
OF 26N W OF 70W. FARTHER EAST OVER THE REMAINDER OF THE W
ATLC...AN UPPER LEVEL TROUGH AXIS EXTENDS FROM 32N69W TO EASTERN
CUBA NEAR 21N77W AND INTO THE WESTERN CARIBBEAN SEA. EAST OF THE
UPPER LEVEL TROUGH AXIS...MIDDLE TO UPPER LEVEL TROPICAL
MOISTURE CONTINUES TO ADVECT NORTHWARD BETWEEN 56W-73W.
SCATTERED SHOWERS AND TSTMS ARE OCCURRING WITHIN 90 NM EITHER
SIDE OF A LINE FROM 17N63W TO 21N70W WITH ISOLATED SHOWERS
OCCURRING ELSEWHERE FROM 11N-32N BETWEEN 57W-73W. THE REMAINDER
OF THE CENTRAL AND EASTERN ATLC IS UNDER THE INFLUENCE OF A
SURFACE RIDGE N OF 20N E OF 55W ANCHORED BY A 1020 MB HIGH
CENTERED NEAR 33N48W AND A 1026 MB HIGH CENTERED EAST OF THE
AZORES NEAR 38N19W. EMBEDDED WITHIN THE SW PERIPHERY OF THIS
SURFACE RIDGE...A WEAK 1010 MB SURFACE LOW IS CENTERED NEAR
17N51W AND CONTINUES TO MOVE WESTWARD. SCATTERED SHOWERS AND
ISOLATED TSTMS ARE OCCURRING WITHIN 120 NM OF THE CENTER OF THE
LOW.

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

$$
HUFFMAN




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