000 AXNT20 KNHC 190005 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT SAT SEP 18 2010 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 2345 UTC. ...SPECIAL FEATURES... HURRICANE IGOR IS CENTERED NEAR 27.7N 64.5W AT 19/0000 UTC OR ABOUT 325 MI...520 KM S OF BERMUDA MOVING NW AT 12 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 945 MB. MAXIMUM SUSTAINED WIND SPEED IS 86 KT WITH GUSTS TO 105 KT. IGOR REMAINS LARGE AND OUTER RAINBANDS ARE EXPECTED TO BEGIN IMPACTING BERMUDA DURING THE NEXT 12-18 HRS. SEE LATEST NHC INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT1/WTNT31 AND THE FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS. NUMEROUS STRONG CONVECTION IS FROM 25N-29N BETWEEN 62W-65W. SCATTERED MODERATE CONVECTION IS ELSEWHERE FROM 23N-30N BETWEEN 61W-68W. TROPICAL STORM JULIA IS CENTERED NEAR 30.6N 51.8W AT 18/2100 UTC OR ABOUT 1500 MI WSW OF THE AZORES MOVING NNW AT 17 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 998 MB. MAXIMUM SUSTAINED WIND SPEED IS 45 KT WITH GUSTS TO 55 KT. WATER VAPOR IMAGERY AND SATELLITE DERIVED WINDS INDICATE THAT THE UPPER LEVEL OUTFLOW OF IGOR CONTINUES TO SHEAR JULIA RESULTING IN FURTHER WEAKENING. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. NUMEROUS STRONG CONVECTION IS FROM 28N-32N BETWEEN 49W-55W WITH SCATTERED MODERATE CONVECTION ELSEWHERE FROM 26N-33N BETWEEN 47W-53W. A SURFACE LOW IS NEAR 12N28W. AN AREA OF DEEP LAYERED MOISTURE SURROUNDS THE SURFACE LOW NOTED ON TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED MODERATE TO ISOLATED STRONG CONVECTION IS FROM 12N-18N BETWEEN 24W AND 32W. ENVIRONMENTAL CONDITIONS ARE GRADUALLY BECOMING MORE FAVORABLE FOR ADDITIONAL DEVELOPMENT OF THIS DISTURBANCE. THERE IS A MEDIUM CHANCE OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS. ...TROPICAL WAVES... NONE ...ITCZ... THE THE ITCZ...OR PERHAPS BETTER DESCRIBED AS MONSOONAL TROUGH BECAUSE OF THE CONVERGENCE OF NE AND SW SURFACE WINDS...REMAINS DISCONTINUOUS ACROSS THE ATLC. SCATTERED MODERATE CONVECTION IS HOWEVER FROM 3N TO 9N BETWEEN THE COAST OF AFRICA AND 30W. SIMILAR CONVECTION IS FROM 6N TO 15N BETWEEN 43W AND 49W. SCATTERED MODERATE TO STRONG CONVECTION IS FROM 12N TO 18N BETWEEN 24W AND 32W ASSOCIATED WITH THE LOW PRESSURE SYSTEM DISCUSSED IN THE SPECIAL FEATURES ABOVE. A SURGE OF SCATTERED MODERATE TO STRONG CONVECTION IS ALONG THE COAST OF AFRICA FROM FROM SIERRA LEONE TO SENEGAL. FURTHER WEST NEAR THE WINDWARD ISLANDS...SCATTERED SHOWERS AND THUNDERSTORMS ARE FROM 7N TO 19N BETWEEN 53W AND 60W...EMBEDDED IN MOISTURE BEING DRAWN NNE BEHIND IGOR. ...DISCUSSION... GULF OF MEXICO... DEEP LAYER MOISTURE AND INSTABILITY REMAINS ACROSS THE W AND NW GULF PRODUCING SCATTERED HEAVY SHOWERS AND THUNDERSTORMS N OF 22N W OF 91W. WITHIN THIS REGION OF CONVECTION...A SURFACE TROUGH IS ANALYZED 75 NM OFF THE COAST FROM MATAGORDA TEXAS SOUTHWARD TO COATZACOALCOS MEXICO. COMPUTER MODELS SUGGEST THIS AREA OF CONVECTION WILL LINGER OVER THE NEXT SEVERAL DAYS. ANTICYCLONIC FLOW ALOFT AROUND AN UPPER RIDGE CENTERED OVER THE SE CONUS BRINGS RELATIVELY DRY AND STABLE AIRMASS TO THE EASTERN HALF OF THE GULF PROMOTING FAIR WEATHER CONDITIONS ACROSS THE REMAINDER OF THE AREA. THE STABILITY IN THIS REGION WILL CONTINUE AND SLOWLY SPREAD WESTWARD OVER THE NEXT SEVERAL DAYS AS THE UPPER RIDGE STRENGTHENS. CARIBBEAN SEA... TOTAL PRECIPITABLE WATER IMAGERY DISPLAYS A STREAM OF DEEP LAYER MONSOONAL MOISTURE MOVING NNE ACROSS THE FAR EASTERN CARIBBEAN. THE MOISTURE FLOW IS DUE TO THE LARGE SCALE CYCLONIC WIND FIELD FROM HURRICANE IGOR. THUS...SCATTERED SHOWERS AND THUNDERSTORMS ARE N OF 12N E OF 67W INCLUDING THE LEEWARD ISLANDS AND PUERTO RICO AS NOTED BY SATELLITE DATA AND DOPPLER RADAR IMAGERY. COMPUTER MODELS SUGGEST THE CONVECTION IS THIS REGION COULD BROADEN AND LINGER OVER THE NEXT SEVERAL DAYS. SCATTERED MODERATE CONVECTION IS ALSO OVER THE SW CARIBBEAN S OF 14N W OF 70W NEAR AN EXTENSION OF THE E PACIFIC MONSOONAL TROUGH EXTENDING ACROSS COSTA RICA TO THE COAST OF COLOMBIA. FAIR WEATHER CONDITIONS WITH A FEW ISOLATED SHOWERS ARE OBSERVED ELSEWHERE ACROSS THE BASIN...DUE TO A DRY AND STABLE AIRMASS ALOFT CAPTURED ON WATER VAPOR IMAGERY. ATLANTIC OCEAN... DRY AND STABLE AIR ALOFT IS OVER THE WESTERN ATLC W OF 71W AROUND THE UPPER LEVEL RIDGE CENTERED OVER THE SE CONUS. HURRICANE IGOR AND TROPICAL STORM JULIA TOGETHER WITH A LOW PRESSURE SYSTEM OVER THE EAST TROPICAL ATLC ARE THE PRIMARY SURFACE FEATURES OVER THE ATLANTIC. SEE SPECIAL FEATURES ABOVE FOR MORE DETAILS. THE LARGE SCALE CYCLONIC WIND FIELD FROM HURRICANE IGOR IS DRAWING A STREAM OF DEEP LAYER MONSOONAL MOISTURE NNE ACROSS THE FAR EASTERN CARIBBEAN AND THE LESSER ANTILLES INTO THE ATLC GENERATING SCATTERED SHOWERS AND THUNDERSTORMS E OF THE LEEWARD ISLANDS FROM 7N TO 19N BETWEEN 53W AND 60W. SURFACE RIDGING IS ELSEWHERE ACROSS THE REGION E OF 46W N OF 18N SUPPORTED BY A BROAD 1027 MB HIGH WEST OF THE AZORES NEAR 37N39W. A LARGE AREA OF AFRICAN DUST FROM THE SAHARA REGION IS NOTED ON SATELLITE IMAGERY...COVERING MOST OF THE EASTERN ATLC FROM 14N TO NORTH OF THE AREA OF DISCUSSION BETWEEN THE COAST OF AFRICA AND 46W. THIS SAHARAN AIR LAYER...ALONG WITH THE SUB-TROPICAL HIGH ARE KEEPING FAIR WEATHER CONDITIONS IN THIS REGION. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ GARCIA