000 AXNT20 KNHC 012357 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT TUE SEP 01 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2330 UTC. ...SPECIAL FEATURES... A TROPICAL SYSTEM E OF THE LESSER ANTILLES HAS BEEN UPGRADED TO TROPICAL STORM ERIKA AS OF 01/2100 UTC. AS OF 02/0000 UTC TROPICAL STORM ERIKA HAS BARELY MOVED FROM ITS PREVIOUS POSITION AND IS CENTERED NEAR 17.2N 57.3W...OR ABOUT 390 MILES E OF THE NRN LEEWARD ISLANDS. ERIKA HAS BEEN MEANDERING FROM THE PAST 3 HOURS BUT IS EXPECTED TO BEGIN MOVING WNW NEAR 8 KT. ESTIMATED CENTRAL PRESSURE IS 1004 MB REPORTED BY AN AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT. MAXIMUM SUSTAINED WINDS ARE 45 KT WITH GUSTS TO 55 KT. PLEASE SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21. TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 105 MILES. NUMEROUS STRONG CONVECTION IS FROM 15N-19N BETWEEN 53W-58W. INTERESTS IN THE NRN LEEWARD ISLANDS...U.S. AND BRITISH VIRGIN ISLANDS...AND PUERTO RICO SHOULD MONITOR THE PROGRESS OF ERIKA. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 20W/21W S OF 20N MOVING W 15-20 KT. UPPER AIR TIME-SECTION ANALYSIS FROM DAKAR SENEGAL INDICATED THAT THIS WAVE PASSED DAKAR AROUND 01/0000 UTC. SATELLITE IMAGERY INDICATES LOW-LEVEL CYCLONIC FLOW IN THE VICINITY OF THE WAVE AXIS. THE WAVE ALSO COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS W OF THE WAVE AXIS FROM 12N-18N BETWEEN 22W-25W. THIS SYSTEM HAS A LOW CHANCE...LESS THAN 30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HRS. A TROPICAL WAVE EXTENDS FROM 16N39W TO 8N35W MOVING W NEAR 20 KT. THE WAVE IS ALONG THE LEADING EDGE OF A MAXIMUM IN DEEP LAYER MOISTURE OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. LOW-LEVEL CYCLONIC FLOW IS IN THE VICINITY OF THE WAVE AXIS AS NOTED IN SATELLITE IMAGERY AND SATELLITE DERIVED WINDS. HOWEVER...THE WAVE IS EMBEDDED WITHIN A DRY SAHARAN AIR LAYER WHICH IS CURRENTLY INHIBITING ANY DEEP CONVECTION NEAR THE WAVE AXIS. A TROPICAL WAVE IS ALONG 86W S OF 14N MOVING W NEAR 20 KT. THIS WAVE CONTINUES TO BE LOCATED BASED ON CONTINUITY AS THERE IS NO CLEAR SIGNATURE IN SURFACE OBSERVATIONS OR SATELLITE IMAGERY. HOWEVER...SCATTERED MODERATE/ISOLATED STRONG CONVECTION HAS RECENTLY POPPED UP NEAR THE WAVE AXIS FROM 10N-16N BETWEEN 84W-86W. THIS ACTIVITY IS PROBABLY ASSOCIATED MORE WITH UPPER LEVEL DIFFLUENCE THAN SURFACE CONVERGENCE NEAR THE WAVE. ...ITCZ... THE ITCZ AXIS IS CENTERED ALONG 14N16W 11N28W 12N35W 9N44W 11N51W. ISOLATED MODERATE CONVECTION IS WITHIN 200NM S OF THE AXIS BETWEEN 37W-48W. ...DISCUSSION... GULF OF MEXICO... AS OF 2100 UTC...A STATIONARY FRONT LINES THE NRN GULF FROM THE FLORIDA PANHANDLE TO SRN TEXAS EXTENDING ALONG 31N82W 30N86W 28N90W 28N97W. ISOLATED SHOWERS ARE WITHIN 200NM AHEAD OF THE FRONT. A SURFACE TROUGH IS ACROSS S FLORIDA FROM A 1014 MB LOW NEAR 26N81W EXTENDING INTO THE SE GULF ALONG 24N83W 23N88W. SURFACE CONVERGENCE NEAR THIS TROUGH IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS THE FLORIDA PENINSULA E OF 83W. BASED ON RECENT LIGHTNING DATA THE MOST ACTIVITY IS LOCATED OVER SRN FLORIDA NEAR THE SURFACE LOW. ANOTHER SURFACE TROUGH IS ACROSS THE YUCATAN PENINSULA AND THE BAY OF CAMPECHE EXTENDING FROM 22N93W TO 17N89W. SURFACE CONVERGENCE NEAR THE TROUGH IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS THE YUCATAN PENINSULA...AND ISOLATED SHOWERS ACROSS THE BAY OF CAMPECHE AND W GULF W OF 93W S OF 25N. IN THE UPPER LEVELS...AN UPPER LEVEL TROUGH IS OVER THE NRN GULF N OF 27N SUPPORTING THE STATIONARY FRONT. AN UPPER LEVEL RIDGE COVERS THE REMAINDER OF THE GULF CENTERED OVER MEXICO NEAR 22N102W. THE WIDTH OF THE RIDGE NARROWS ACROSS THE SE GULF AND EXTENDS ACROSS S FLORIDA AND INTO THE ATLC. UPPER LEVEL DIVERGENCE BETWEEN THE UPPER RIDGE AND UPPER TROUGH IS ENHANCING THE AFOREMENTIONED AREAS OF SHOWERS/THUNDERSTORMS. CARIBBEAN SEA... AN UPPER LEVEL RIDGE COVERS THE WRN CARIBBEAN CENTERED NEAR 17N83W. UPPER LEVEL DIFFLUENCE BETWEEN THIS RIDGE AND AN UPPER LEVEL TROUGH S OF CENTRAL AMERICA IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS ERN HONDURAS AND NRN NICARAGUA. ISOLATED SHOWERS ARE ALSO ACROSS THE FAR NW CARIBBEAN. UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER RIDGE AND A SHORTWAVE UPPER TROUGH EXTENDING LATERALLY ACROSS CUBA FROM A LARGER UPPER LEVEL TROUGH OVER THE ATLC ACROSS HISPANIOLA AND INTO THE CENTRAL CARIBBEAN IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS CUBA AND THE ADJACENT COASTAL WATERS. A SURFACE TROUGH ACROSS THE CENTRAL BAHAMAS EXTENDS TO NRN CUBA NEAR 21N76W. SURFACE CONVERGENCE NEAR THE TROUGH IS ALSO ENHANCING THE SHOWER ACTIVITY ACROSS CUBA. ELSEWHERE ACROSS THE CARIBBEAN...DRY AIR AND SUBSIDENCE ALOFT IS SUPPORTING GENERALLY FAIR WEATHER BESIDES A FEW ISOLATED SHOWERS E OF 66W DUE TO MOIST SLY FLOW ALOFT AROUND AN UPPER LEVEL RIDGE E OF THE LESSER ANTILLES. MODERATE TO FRESH TRADE WINDS ARE ACROSS MUCH OF THE BASIN WITH STRONGER WINDS NEAR THE COAST OF COLUMBIA. INTERESTS IN THE NRN LEEWARD ISLANDS...U.S. AND BRITISH VIRGIN ISLANDS...AND PUERTO RICO SHOULD MONITOR THE PROGRESS OF TROPICAL STORM ERIKA...SEE SPECIAL FEATURES ABOVE. ATLANTIC OCEAN... THE MAIN FOCUS FOR THE ATLC BASIN TONIGHT IS TROPICAL STORM ERIKA. SEE SPECIAL FEATURES ABOVE. IN THE W ATLC...AS OF 2100 UTC...A STATIONARY FRONT EXTENDS ACROSS THE NRN GULF TO NRN FLORIDA NEAR 31N81W EXTENDING OUT OF THE DISCUSSION AREA NEAR 32N77W. A SURFACE TROUGH IS OUT AHEAD OF THE FRONT FROM A 1014 MB LOW OVER S FLORIDA NEAR 26N81W EXTENDING TO 31N78W. SURFACE CONVERGENCE NEAR THE FRONT AND SURFACE TROUGH IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS NW OF A LINE FROM 24N81W TO 31N71W. RECENT LIGHTNING ACTIVITY INDICATES THAT THE MOST ACTIVE THUNDERSTORMS ARE LOCATED OVER S FLORIDA AND THE ADJACENT WATERS. A SURFACE TROUGH EXTENDS FROM NRN CUBA NEAR 21N76W TO 28N74W. SURFACE CONVERGENCE NEAR THIS TROUGH IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS CUBA...AND ISOLATED SHOWERS ACROSS THE BAHAMAS AND HISPANIOLA FROM 19N-27N W OF 68W. ELSEWHERE ACROSS THE ATLC...A BROAD SURFACE RIDGE DOMINATES ANCHORED BY A 1031 MB HIGH NEAR 36N39W. IN THE UPPER LEVELS...AN UPPER LEVEL TROUGH IS OVER THE ERN CONUS WHILE A SHORTWAVE UPPER RIDGE EXTENDS ACROSS S FLORIDA CONTINUING ALONG 27N80W TO 38N62W. UPPER LEVEL DIFFLUENCE BETWEEN THESE FEATURES IS SUPPORTING THE SHOWER ACTIVITY IN THE WRN ATLC. E OF THE UPPER RIDGE AN UPPER LEVEL TROUGH EXTENDS ALONG 35N57W TO HISPANIOLA CONTINUING INTO THE CENTRAL CARIBBEAN. AN UPPER LEVEL RIDGE IS E OF THE LESSER ANTILLES CENTERED NEAR 18N51W SUPPORTING TROPICAL STORM ERIKA. A LATERALLY ORIENTED UPPER LEVEL TROUGH DOMINATES THE E ATLC WITH AXIS ALONG 25N. ACROSS THE TROPICAL ATLC...AN UPPER LEVEL RIDGE IS S OF 20N E OF 32W. ENTERS THE DISCUSSION AREA NEAR 31N81 AND EXTENDS TO NEAR SAINT AUGUSTINE FLORIDA. A PRE-FRONTAL TROUGH IS ALSO ANALYZED S OF THE FRONTAL BOUNDARY FROM 32N77W TO WEST PALM BEACH FLORIDA. SCATTERED SHOWERS AND TSTMS ARE OCCURRING WITHIN 150 NM E OF THE SURFACE TROUGH N OF 27N. FARTHER TO THE E...AN UPPER LEVEL LOW IS CENTERED N OF THE AREA NEAR 33N61W AND EXTENDS TROUGHING SW TO OVER HISPANIOLA AND INTO THE CENTRAL CARIBBEAN. A SURFACE TROUGH IS ANALYZED FROM 27N76W TO THE WINDWARD PASSAGE. SCATTERED SHOWERS AND ISOLATED TSTMS ARE OCCURRING E OF THE SURFACE TROUGH FROM 20N-26N BETWEEN 67W-73W. ELSEWHERE ACROSS THE REMAINDER OF THE CENTRAL AND ERN ATLC...THE BASIN REMAINS FAIRLY BENIGN AS A SURFACE RIDGE CONTROLS N OF 20N E OF 65W AND IS ANCHORED BY A 1031 MB SURFACE HIGH CENTERED N OF THE REGION WSW OF THE AZORES NEAR 37N36W. $$ HUFFMAN