000 AXNT20 KNHC 181803 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT WED SEP 18 2013 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 1715 UTC. ...SPECIAL FEATURES... TROPICAL STORM HUMBERTO IS CENTERED AT 31.3N 43.8W AT 18/1500 UTC OR ABOUT 920 NM W-SW OF THE AZORES MOVING N-NW AT 4 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1007 MB. MAXIMUM SUSTAINED WIND SPEED IS 35 KT WITH GUSTS TO 45 KT. PLEASE SEE LATEST PUBLIC ADVISORIES UNDER AWIPS/WMO HEADERS MIATCPAT4/WTNT34 AND THE FULL FORECAST ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/ WTNT24 FOR MORE DETAILS. CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION ARE WITHIN 90/120 NM OF LINE FROM 29N39W 31N41W TO 32N45W. BROAD AREA OF LOW PRESSURE IS ANALYZED AS A SURFACE TROUGH THAT EXTENDS FROM 22N90W THROUGH A 1004 MB LOW NEAR 20N90W TO N GUATEMALA NEAR 17N90W. AN UPPER RIDGE IS TO THE E PROVIDING A DIFFLUENT ENVIRONMENT. SCATTERED TO HEAVY SHOWERS WITH EMBEDDED THUNDERSTORMS COVER THE AREA FROM 18N-22N BETWEEN 80W-90W. THIS SYSTEM AT 18/1800 UTC IS NOW CENTERED W OF THE YUCATAN PENINSULA IN THE BAY OF CAMPECHE BUT REMAINS POORLY ORGANIZED. THIS SYSTEM IS EXPECTED TO MOVE W-NW OVER THE SW GULF OF MEXICO DURING THE NEXT COUPLE OF DAYS WHERE ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE CONDUCIVE FOR THE FORMATION OF A TROPICAL DEPRESSION. THIS SYSTEM HAS A HIGH CHANCE OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS. REGARDLESS OF DEVELOPMENT... THIS DISTURBANCE WILL LIKELY SPREAD HEAVY RAINS OVER PORTIONS OF EASTERN MEXICO AND COULD CAUSE LIFE-THREATENING FLOODS AND MUDSLIDES OVER AREAS ALREADY IMPACTED BY TORRENTIAL RAINS DURING THE PAST SEVERAL DAYS. ...TROPICAL WAVES... TROPICAL WAVE IS W OF THE CAPE VERDE ISLANDS EXTENDING FROM 21N25W TO 13N28W MOVING W NEAR 5 KT. WAVE IS ALONG THE LEADING EDGE OF SURGE OF DEEP MOISTURE AS DEPICTED ON THE TOTAL PRECIPITABLE WATER IMAGERY. NO ASSOCIATED CONVECTION. ...THE ITCZ/THE MONSOON TROUGH... THE MONSOON TROUGH EXTENDS ACROSS AFRICA INTO THE E TROPICAL ATLC NEAR 13N16W AND CONTINUES ALONG 13N19W TO 10N26W WHERE THE ITCZ BEGINS AND CONTINUES ALONG 9N36W 9N47W TO 11N58W. CLUSTERS OF SCATTERED MODERATE TO ISOLATED STRONG CONVECTION FROM 7N-10N BETWEEN 18W-37W. A SURFACE TROUGH EXTENDS FROM 18N48W TO 11N47W WITH CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION WITHIN 75 NM OF LINE FROM 13N42W TO THE TROUGH NEAR 16N48W. ...DISCUSSION... GULF OF MEXICO... FEATURE TO WATCH THIS AFTERNOON IS THE LOW/SURFACE TROUGH IN THE SPECIAL FEATURES ABOVE. A BROAD UPPER RIDGE IS ANCHORED OVER MEXICO EXTENDING A RIDGE AXIS ACROSS THE GULF FROM TAMPICO MEXICO TO SE LOUISIANA. AN UPPER RIDGE IS OVER THE NW CARIBBEAN CLIPPING THE SE GULF S OF 25N E OF 85W AND IS PROVIDING DIFFLUENCE ALOFT TO GENERATE SCATTERED SHOWERS/ISOLATED THUNDERSTORMS S OF 26N BETWEEN 80W-85W. THIS SCENARIO IS INDUCING AN UPPER TROUGH THAT EXTENDS FROM THE BROAD UPPER TROUGH IN THE W ATLC ACROSS NE FLORIDA TO 24N87W. THE UPPER TROUGH OVER THE W ATLC IS SUPPORTING A STATIONARY FRONT THAT EXTENDS ACROSS FLORIDA FROM SAINT AUGUSTINE CLIPPING APALACHEE BAY ALONG 30N85W CONTINUING INLAND ALONG THE N GULF COAST TO S LOUISIANA. ISOLATED SHOWERS/THUNDERSTORMS DOT THE REMAINDER OF THE GULF THIS AFTERNOON. THE LOW/TROUGH WILL CONTINUE TO MOVE TO THE W-NW POSSIBLY AS A TROPICAL CYCLONE...AND STALL IN THE W GULF FRI. THE LOW MAY MOVE SLOWLY E-NE ALONG A COLD FRONT ENTERING THE NW GULF LATE FRI NIGHT OR WILL STALL OUT AND GET LEFT BEHIND IN THE W CENTRAL GULF THROUGH THE WEEKEND. CARIBBEAN SEA... AN UPPER RIDGE COVERS THE W CARIBBEAN W OF 70W ANCHORED NEAR 20N85W AND PROVIDING A DIFFLUENT ENVIRONMENT FOR THE LOW/SURFACE TROUGH IN THE SPECIAL FEATURES ABOVE. BENEATH THIS UPPER FLOW IS A WEAK 1008 MB LOW IN THE SW CARIBBEAN NEAR 11N79W. THE MONSOON TROUGH EXTENDS FROM COLOMBIA NEAR 10N75W THROUGH THE ABOVE 1008 MB LOW TO OVER NICARAGUA NEAR 13N84W. SCATTERED/NUMEROUS SHOWERS WITH EMBEDDED THUNDERSTORMS ARE FROM 10N-13N BETWEEN 76W-81W WITH SCATTERED SHOWERS/ISOLATED THUNDERSTORMS S OF 14N TO INLAND OVER COLOMBIA/PANAMA BETWEEN 74W-83W. AN UPPER LOW N OF PUERTO RICO EXTENDS AN UPPER TROUGH ACROSS PUERTO RICO TO THE ABC ISLANDS. AN E/W UPPER RIDGE ANCHORED IN THE TROPICAL ATLC EXTENDS OVER THE REMAINDER OF THE E CARIBBEAN. THIS UPPER RIDGE IS PROVIDING DIFFLUENCE ALOFT TO GENERATE SCATTERED SHOWERS/ ISOLATED THUNDERSTORMS FROM 12N-16N E OF 66W TO OVER THE LESSER ANTILLES. THIS IS LEAVING THE REMAINDER OF THE CARIBBEAN WITH FAIR WEATHER THIS AFTERNOON. FRESH TO STRONG TRADE WINDS ACROSS THE S/CENTRAL AND NW CARIBBEAN WILL DIMINISH TO MODERATE BY FRI. GENTLE TO MODERATE E TRADE WINDS WILL CONTINUE ACROSS THE AREA E OF 70W THROUGH SUN. HISPANIOLA... DAYTIME HEATING IS BEGINNING TO DEVELOP CLOUDS AND ISOLATED SHOWERS ACROSS THE ISLAND WHERE SKIES HAD BEEN CLEAR THIS MORNING. AN UPPER LEVEL TROUGH IS JUST TO THE E OF HISPANIOLA AND WILL REMAIN IN PLACE THROUGH SAT THEN BROADEN OUT THROUGH SUN WHEN THE UPPER FLOW WILL BECOME WESTERLY. AFTERNOON SHOWERS/THUNDERSTORMS COULD DEVELOP DAILY WITH THE DAYTIME HEATING. ATLANTIC OCEAN... THE PRIMARY CONCERN THIS AFTERNOON IS T.S. HUMBERTO IN THE CENTRAL ATLC. SEE SPECIAL FEATURES ABOVE. BROAD UPPER TROUGH COVERS THE W ATLC N OF 27N W OF 60W SUPPORTING A COLD FRONT THAT ENTERS THE REGION NEAR 32N61W EXTENDING TO 29N68W WHERE IT BECOMES STATIONARY ALONG 29N76W THEN ACROSS NE FLORIDA NEAR SAINT AUGUSTINE. A SURFACE TROUGH IS TO THE S EXTENDING FROM 28N68W TO 24N72W. CLUSTERS OF SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ARE FROM 24N TO THE FRONT BETWEEN 60W-76W AND N OF 29N W OF 79W. A SURFACE RIDGE COVERS THE E ATLC E OF T.S. HUMBERTO ANCHORED BY A 1028 MB HIGH NE OF THE AZORES. THE FRONT OVER THE W ATLC WILL DISSIPATE BY THU NIGHT. A BROAD SURFACE TROUGH WILL PREVAIL FROM THE CENTRAL ATLC TO THE BAHAMAS THROUGH SAT WITH THE POSSIBILITY OF A SURFACE LOW FORMING ALONG THE TROUGH. THE TROUGH WILL FINALLY MOVE INTO THE CENTRAL ATLC ON SUN. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ PAW