000 AXNT20 KNHC 151804 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT FRI SEP 15 2006 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHEASTERN SECTIONS OF SOUTH AMERICA...AND THE 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 1315 UTC. ...SPECIAL FEATURES... HURRICANE GORDON WAS CENTERED NEAR 31.1N 53.3W AT 15/1500 UTC MOVING NORTHEAST AT 6 KT. THIS MOTION IS EXPECTED TO CONTINUE FOR THE NEXT 24 HOURS WITH A CONTINUED DECREASE IN FORWARD SPEED. ESTIMATED MINIMUM CENTRAL PRESSURE IS 973 MB. MAXIMUM SUSTAINED WINDS ARE 85 KT WITH GUSTS TO 105 KT. GORDON REMAINS A CATEGORY TWO HURRICANE ON THE SAFFIR-SIMPSON HURRICANE SCALE. ADDITIONAL WEAKENING IS FORECAST DURING THE NEXT 24 HOURS.SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. INFRARED IMAGERY HAS SHOWN THAT THE CLOUD TOPS NEAR THE CENTER OF GORDON HAVE WARMED A BIT THIS MORNING. SCATTERED MODERATE CONVECTION NOW LIES FROM 30N-33N BETWEEN 52W-56W. TROPICAL STORM HELENE WAS CENTERED NEAR 15.8N 41.4W AT 15/1500 UTC MOVING WEST-NORTHWEST AT 11 KT. THIS MOTION IS EXPECTED TO CONTINUE DURING THE NEXT DAY OR TWO. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1000 MB. MAXIMUM SUSTAINED WINDS ARE 50 KT WITH GUSTS TO 60 KT. SOME STRENGTHENING IS FORECAST DURING THE NEXT 24 HOURS AND HELENE COULD BECOME A HURRICANE ON SATURDAY. SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS. GOES AND METEOSAT SATELLITE IMAGES INDICATE THAT THE CLOUD PATTERN IS BETTER ORGANIZED AND IS MORE TYPICAL OF A TROPICAL STORM. THE CONVECTION IS MORE CONCENTRATED NEAR THE CENTER...AND THERE IS A WELL-DEFINED CYCLONICALLY CURVED BAND TO THE SOUTH WITH NUMEROUS RAINBANDS ALL AROUND. SCATTERED MODERATE/ISOLATED STRONG CONVECTION EXISTS FROM 12N-19N BETWEEN 38W-45W. ...TROPICAL WAVES... A TROPICAL WAVE HAS EMERGED OFF THE COAST OF AFRICA ALONG 19W/20W S OF 18N MOVING W NEAR 10 KT. THIS WAVE IS ACCOMPANIED BY A 1013MB SURFACE LOW NEAR 14N. BROAD CYCLONIC CURVATURE IS CLEARLY NOTED IN THE LOW TO MID CLOUD FIELD...AND IN THE AVAILABLE SURFACE OBSERVATIONS. CLOUD TOPS ASSOCIATED WITH THIS WAVE HAVE WARMED A FEW DEGREES OVER THE LAST FEW HOURS...THOUGH SCATTERED MODERATE STILL EXISTS FROM 12N-18N BETWEEN 18W-23W. TROPICAL WAVE IS ALONG 61W/62W S OF 15N MOVING W NEAR 15 KT. THIS IS A LOW AMPLITUDE WAVE THAT IS NOT EASY TO IDENTIFY ON SATELLITE IMAGERY. THERE HAS BEEN SOME SUBTLE TURNING IN THE WIND FIELD IN THE SRN LESSER ANTILLES BUT SOME OF THIS MAY BE DIURNALLY INDUCED. DEEP CONVECTION REMAINS MINIMAL NEAR THIS WAVE...ASIDE FROM SMALL CLUSTERS OF MODERATE CONVECTION NEAR THE ITCZ AND NE S AMERICA BETWEEN 58W-63W. TROPICAL WAVE IS ALONG 73W S OF 18N MOVING W 10 TO 15 KT. THIS WAVE EXHIBITS AN INVERTED V PATTERN ON SATELLITE IMAGERY...WITH ISOLATED AND TSTMS N OF 14N TO THE COAST OF HISPANIOLA BETWEEN 68W-75W. TROPICAL WAVE IS ALONG 81W/82W S OF 15N MOVING W 10 TO 15 KT. THIS WAVE HAS BEEN REPOSITIONED SLIGHTLY TO THE E OF THE PREVIOUS POSITION DUE TO THIS MORNINGS VISIBLE SATELLITE IMAGERY...AND THE CONVECTIVE PATTERN IN THE SW CARIBBEAN. SCATTERED MODERATE CONVECTION SEEN FROM 9N-14N BETWEEN 77W AND 84W. THIS ACTIVITY IS BEGINNING TO SPREAD INTO COASTAL CENTRAL AMERICA. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 13N23W 16N36W 11N44W 10N60W. SCATTERED STRONG CONVECTION IS WITHIN 150 NM N OF THE AXIS E OF 18W TO INLAND OVER AFRICA. OUTSIDE OF THE CONVECTION ASSOCIATED WITH THE TROPICAL WAVES AND HELENE...CLUSTERS OF SCATTERED MODERATE CONVECTION ARE SEEN FROM 12N-14N BETWEEN 29W-32W AND 13N-17N BETWEEN 33W-37W (JUST E OF HELENE). SCATTERED SHOWERS/ISOLATED TSTMS APPROACHING NE S AMERICA FROM 7N-9N BETWEEN 54W-60W. ...DISCUSSION... GULF OF MEXICO... BROAD DEEP LAYERED TROUGH COVERS THE E US...THE W ATLC AND ERN GULF IS ANCHORED BY AN UPPER LOW MOVING SSW THROUGH UPSTATE NEW YORK. UPPER DIFFLUENT AIR BETWEEN THE WRLY FLOW AROUND THE SSW PORTION OF THIS UPPER TROUGH...AND NRLY FLOW AROUND AN UPPER HIGH OVER CENTRAL MEXICO...IS HELPING TO SUPPORT THE SCATTERED SHOWERS AND TSTMS IN THE MIDDLE GULF FROM 24N-28N BETWEEN 90W=94W. LOW CLOUD MOTIONS AND SFC OBSERVATIONS IN THE ERN GULF SUGGESTS A WEAK SFC HIGH MAY HAVE FORMED NEAR 25N86W. E OF THIS AREA LIES THE COLD FRONT BOUNDARY WE HAVE BEEN TRACKING THAT EXTENDS THROUGH THE SW NORTH ATLC AND OVER SRN FLORIDA. CARIBBEAN SEA... THE MAJORITY OF THE WEATHER IN THE CARIBBEAN THIS AFTERNOON IS BEING PRODUCED BY THE TROPICAL WAVES MOVING THROUGH AS DESCRIBED ABOVE. THE W/NW CARIBBEAN IS DOMINATED BY NE UPPER FLOW...WITH AN UPPER TROUGH AXIS EXTENDING THROUGH CENTRAL AMERICA AND ERN CUBA ALONG 15N84W 20N77W. A SMALL MID TO UPPER LEVEL ANTICYCLONE IS DRIFTING N THROUGH THE CENTRAL CARIBBEAN...CENTERED NEAR 15N74W. THE FAR ERN CARIBBEAN HAS VERY DRY MID TO UPPER LEVEL AIR BEING ADVECTED INTO THE REGION FROM THE E...AROUND THE ERLY FLOW SSW OF THE UPPER ANTICYCLONE IN THE TROPICAL ATLC NEAR 22N59W. 10 TO 20 KT TRADES DOMINATE MUCH THE THE AREA...EXCEPT SLIGHTLY STRONGER JUST N OF THE COLOMBIAN/VENEZUELAN COASTS AND SLIGHTLY WEAKER FAR NW PORTION. ATLANTIC OCEAN... BROAD DEEP LAYERED TROUGH THAT COVERS THE E US AND ERN GULF HAS AN ASSOCIATED FRONTAL BOUNDARY THAT EXTENDS NE FROM SOUTH CENTRAL FLORIDA AND INTO THE TROPICAL SW NORTH ATLC ALONG 26N81W 31N74W. PREFRONTAL LIFT IS GENERATING NUMEROUS SHOWERS AND TSTMS MAINLY WITHIN 100NM SE OF THE ANALYZED COLD FRONT BOUNDARY. A NARROW MID TO UPPER LEVEL RIDGE AXIS LIES JUST E OF THIS FRONTAL SYSTEM...ALONG 24N79W 27N73W 31N65W. THERE ALSO APPEARS TO BE SOME LOW LEVEL CONFLUENCE IN THIS REGION ASSOCIATED WITH THE PREFRONTAL SW FLOW MEETING THE SE/S FLOW AROUND THE 1016 ISOBAR THAT CURVES ANTICYCLONICALLY FROM THE 1027MB HIGH S OF THE AZORES. THIS IS HELPING TO PRODUCE THE SCATTERED SHOWERS AND TSTMS BETWEEN THE SE BAHAMAS AND 30N68W. A SMALL UPPER LOW IS SEEN NEAR 30N60W. S OF THIS LIES A WELL DEFINED MID TO UPPER HIGH NEAR 21N59W. A BROAD UPPER RIDGE EXTENDS W FROM THE AFRICAN COAST TO NEAR 35W MAINLY N OF 20N...WITH AN EMBEDDED UPPER LOW SEEN NEAR 20N24W. THE CENTRAL AND ERN ATLC SURFACE PATTERN IS DOMINATED BY HURRICANE GORDON NEAR 31N53W...T.S. HELENE NEAR 16N41W...THE TROPICAL WAVE MOVING OFF THE AFRICAN COAST...AND THE 1027MB SURFACE HIGH S OF THE AZORES NEAR 34N25W. $$ WILLIS