000
AXNT20 KNHC 191736
TWDAT 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SAT SEP 19 2009

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...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1715 UTC.

...SPECIAL FEATURES...
BROAD AREA OF LOWER PRESSURE IS ANALYZED AS A 1008 MB LOW 
CENTERED ABOUT 1100 NM E OF THE WINDWARD ISLANDS NEAR 13.5N42W 
AND HAS BECOME BETTER ORGANIZED THIS MORNING. THIS SYSTEM HAS 
THE POTENTIAL TO BECOME A TROPICAL DEPRESSION OVER THE NEXT DAY 
OR TWO AS IT MOVES TO THE WNW NEAR 10 KT. BROAD AREA OF 
SCATTERED MODERATE WITH EMBEDDED CLUSTERS OF ISOLATED STRONG 
CONVECTION COVERS THE AREA FROM 10N-17N BETWEEN 37W-45W. 

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 28W/29W S OF 17N MOVING W NEAR 10 KT. 
SMALL BUT BROAD LOWER LEVEL CYCLONIC ROTATION IS OBSERVED ALONG 
THE WAVE AXIS WHICH WILL BE DIFFICULT TO DISTINGUISH AT NIGHT. 
SCATTERED MODERATE/STRONG CONVECTION IS FROM 15N-17N BETWEEN 
27W-29W. 

TROPICAL WAVE IS ALONG 93W/94W S OF 20N MOVING W NEAR 15 KT. 
WAVE IS MOSTLY IN THE E PACIFIC REGION WITH A SMALL AREA OF 
INVERTED TROUGH IN THE BAY OF CAMPECHE. SCATTERED SHOWERS/ 
ISOLATED THUNDERSTORMS ARE WITHIN 60 NM OF THE WAVE AXIS IN THE 
BAY OF CAMPECHE. 

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 17N15W 16N26W 14N32W 15N38W 
13N47W 10N62W. AN ELONGATED MID LEVEL LOW IS N OF THE ITCZ NEAR 
19N21W WITH SCATTERED MODERATE CONVECTION WITHIN 90 NM OF LINE 
FROM 22N20W TO 17N21W. 

...DISCUSSION...

GULF OF MEXICO...
AT 1500 UTC...A SURFACE TROUGH EXTENDS INTO THE GULF OF MEXICO 
FROM A 1014 MB LOW OVER SW MISSISSIPPI ACROSS SE LOUISIANA NEAR 
29N91W TO 25N95W WHILE A SECOND SURFACE TROUGH EXTENDS ACROSS S 
FLORIDA INTO THE GULF NEAR NAPLES TO 25N84W. AT THE UPPER 
LEVELS...AN UPPER RIDGE COVERS THE W GULF W OF 90W ANCHORED OVER 
S/CENTRAL MEXICO WHILE A SECOND UPPER RIDGE COVERS MOST OF THE E 
GULF S OF 28N E OF 87W ANCHORED IN THE STRAITS OF FLORIDA NEAR 
24N81W. THIS IS INDUCING AN UPPER TROUGH S OVER THE CENTRAL GULF 
FROM THE FLORIDA/ALABAMA BORDER TO THE YUCATAN PENINSULA. 
DIFFLUENCE ALOFT IS GENERATING SCATTERED SHOWERS/THUNDERSTORMS 
WITHIN 90 NM ALONG THE COAST OF MEXICO S OF 25N W OF 94W WITH 
SCATTERED SHOWERS/ISOLATED THUNDERSTORMS OVER THE SE GULF S OF 
28N E OF 87W WITH THE HIGHEST CONCENTRATION OF THUNDERSTORMS IN 
FLORIDA BAY. ISOLATED SHOWERS ARE OVER THE NE GULF N OF 29N 
BETWEEN APALACHEE BAY FLORIDA AND THE MISSISSIPPI/LOUISIANA 
BORDER. 

CARIBBEAN SEA...
AN INVERTED UPPER TROUGH EXTENDS FROM PANAMA/COSTA RICA BORDER 
NNE TO JAMAICA AS THE UPPER RIDGE IN THE SE GULF OF MEXICO 
COVERS THE FAR NW CARIBBEAN PROVIDING DIFFLUENCE ALOFT TO 
GENERATE CLUSTERS OF SCATTERED SHOWERS/ISOLATED THUNDERSTORMS W 
OF A LINE FROM THE ISTHMUS OF PANAMA TO SW HAITI TO INLAND OVER 
CENTRAL AMERICA AND TO THE COAST OF CUBA. A SECOND UPPER RIDGE 
ANCHORED OVER SOUTH AMERICA COVERS THE SE CARIBBEAN WITH AN 
UPPER LOW JUST N OF THE NE CARIBBEAN PRODUCING SCATTERED SHOWERS 
AND POSSIBLE ISOLATED THUNDERSTORMS OVER THE LEEWARD ISLANDS 
FROM GUADELOUPE TO THE VIRGIN ISLANDS WITH SHOWERS DEVELOPING 
INLAND OVER PUERTO RICO. THE REMAINDER OF THE CARIBBEAN IS 
RATHER TRANQUIL THIS AFTERNOON. 

ATLANTIC OCEAN...
AT 1500 UTC...A SURFACE TROUGH EXTENDS FROM NEAR 32N71W JUST N 
OF NORTHERN BAHAMA ISLANDS ACROSS S FLORIDA NEAR FORT LAUDERDALE 
INTO THE GULF OF MEXICO. SCATTERED SHOWERS/ISOLATED 
THUNDERSTORMS ARE S OF 28N W OF 76W TO INLAND OVER S FLORIDA. AT 
1200 UTC...A 1012 MB LOW...REMNANTS OF FRED IS CENTERED 26N70W 
WITH A SURFACE TROUGH EXTENDING FROM 31N69W THROUGH THE LOW TO 
24N70W. HOWEVER...THE LOW IS BECOMING ELONGATED ALONG THE TROUGH 
AXIS AS OF 1500 UTC. SCATTERED SHOWERS/THUNDERSTORMS ARE WITHIN 
75 NM OF LINE FROM 27N70W TO BEYOND 32N67W. BROAD UPPER LOW 
COVERS THE W/CENTRAL ATLC FROM 17N-28N BETWEEN 53W-69W 
GENERATING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WITHIN 
120 NM OF LINE FROM 15N58W 20N63W TO 23N67W INCLUDING THE 
LEEWARD AND VIRGIN ISLANDS. THE REMAINDER OF THE ATLC N OF 20N E 
OF 60W IS DOMINATED BY A SURFACE RIDGE ANCHORED BY A PAIR OF 
1026 MB HIGHS...ONE NEAR 33N43W AND A SECOND NE OF MADEIRA 
ISLANDS. 

$$
WALLACE