000 AXNT20 KNHC 151805 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT WED SEP 15 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1715 UTC. ...SPECIAL FEATURES... TROPICAL STORM KARL IS CENTERED NEAR 18.8N 88.7W AT 15/1800 UTC OR ABOUT 30 NM NE OF CHETUMAL MEXICO OR ABOUT 120 NM ESE OF CAMPECHE MEXICO MOVING W AT 12 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 994 MB. MAXIMUM SUSTAINED WIND SPEED IS 45 KT WITH GUSTS TO 55 KT. SEE LATEST NHC INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT3/WTNT33 AND THE FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS. NUMEROUS STRONG CONVECTION IS WITHIN 60 NM OF THE CENTER IN THE ALL QUADRANTS WITH SCATTERED MODERATE/STRONG CONVECTION COVERING THE REMAINDER OF THE AREA WITHIN 120 NM OF THE CENTER IN ALL QUADRANTS. KARL SHOULD WEAKEN TODAY AS THE CENTER CROSSES THE YUCATAN PENINSULA. RE-INTENSIFICATION IS EXPECTED ON THURSDAY OR FRIDAY AFTER THE CENTER EMERGES INTO THE BAY OF CAMPECHE. HURRICANE IGOR IS CENTERED NEAR 19.8N 55.0W AT 15/1500 UTC OR ABOUT 470 NM ENE OF THE NORTHERN LEEWARD ISLANDS AND ABOUT 915 NM KM SE OF BERMUDA MOVING W-NW AT 7 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 942 MB. MAXIMUM SUSTAINED WIND SPEED IS 115 KT WITH GUSTS TO 140 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS. NUMEROUS STRONG CONVECTION IS WITHIN 60 NM FROM THE CENTER IN THE N SEMICIRCLE AND 120 NM IN THE S SEMICIRCLE. SCATTERED MODERATE/ISOLATED STRONG CONVECTION COVERING THE REMAINDER OF THE AREA WITHIN 120 NM FROM THE CENTER IN THE N SEMICIRCLE AND 180 NM IN THE S SEMICIRCLE. SOME FLUCTUATIONS IN STRENGTH ARE POSSIBLE DURING THE NEXT OR TWO...BUT IGOR IS EXPECTED TO REMAIN A DANGEROUS HURRICANE. HURRICANE JULIA IS CENTERED NEAR 18.2N 32.7W AT 15/1500 UTC OR ABOUT 515 NM WNW OF THE CAPE VERDE ISLANDS MOVING NW AT 15 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 950 MB. MAXIMUM SUSTAINED WIND SPEED IS 115 KT WITH GUSTS TO 140 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. NUMEROUS STRONG CONVECTION IS WITHIN 90 NM FROM THE CENTER IN THE SW SEMICIRCLE AND 60 NM FROM THE CENTER IN THE NE SEMICIRCLE. SCATTERED MODERATE/ ISOLATED STRONG CONVECTION COVERING THE REMAINDER OF THE AREA WITHIN 120 NM FROM THE CENTER. JULIA IS EXPECTED TO MAINTAIN ITS INTENSITY TODAY BEFORE SLOWLY WEAKENING LATER ON THURSDAY. ...ITCZ... THE ITCZ...OR PERHAPS BETTER DESCRIBED TODAY AS A MONSOONAL TROUGH BECAUSE OF THE CONVERGENCE OF NE AND SW SURFACE WINDS...REMAINS DISCONTINUOUS ACROSS THE ATLANTIC DUE TO HURRICANES IGOR AND JULIA. THE AXIS OF THE ITCZ EXTENDS FROM 10N14W TO 11N26W AND AGAIN FROM 10N36N TO 11N44W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 120 NM N OF THE AXIS FROM 14W TO 26W. ...DISCUSSION... GULF OF MEXICO... AT THE SURFACE...MODERATE RIDGING COVERS THE GULF WITH WEAK E WINDS PREDOMINATING...EXCEPT FOR NEAR THE YUCATAN CHANNEL. NEAR THE LATTER...THE OUTER RAINBANDS FROM TROPICAL STORM KARL ARE PRODUCING SCATTERED SHOWERS AND THUNDERSTORMS WITH WINDS UP TO 25 KT. SCATTERED SHOWERS AND THUNDERSTORMS ARE ALSO PREVALENT OVER AND TO THE WEST OF THE FLORIDA KEYS...PERHAPS ALSO PARTLY IN ASSOCIATION WITH THE OUTER CIRCULATION OF THE TROPICAL STORM. IN THE UPPER LEVELS...A BROAD ANTICYCLONE IS CENTERED NEAR 28N87W WITH DRY...SUBSIDENT CONDITIONS OBSERVED IN THE NORTHERN HALF OF THE GULF. OUTFLOW FROM KARL IS ENHANCING THE ANTICYCLONE FLOW COVERING THE GULF. CARIBBEAN SEA... TROPICAL STORM KARL...WHICH HAS NOW MADE LANDFALL NEAR THE BELIZE-MEXICO BORDER...IS THE MAIN WEATHER FEATURE OVER THE CARIBBEAN AND CENTRAL AMERICA. IN ADDITION TO THE CONVECTIVE STRUCTURES ASSOCIATED WITH THE CYCLONE NOTED ABOVE...NUMEROUS MODERATE/ISOLATED STRONG CONVECTION IS OBSERVED IN SOME BANDING FEATURES FROM KARL SOUTH OF CUBA AND OVER THE EXTREME NW CARIBBEAN SEA. AWAY FROM KARL...WINDS ARE QUITE WEAK FROM THE EAST. THE ONE EXCEPTION IS FOR SOME OF THE LESSER ANTILLES WHICH HAVE EITHER CALM WINDS OR WEAKLY N TO W WINDS...DUE TO THE LARGE WIND FIELD OF HURRICANE IGOR. IN THE UPPER LEVELS...N TO NE FLOW IN THE WESTERN AND CENTRAL CARIBBEAN PREVAILS UNDER THE INFLUENCE OF THE AFOREMENTIONED UPPER RIDGE IN THE NORTHERN GULF. IN THE EASTERN CARIBBEAN...A WEAK UPPER TROUGH IS OBSERVED AND IS ASSOCIATED WITH QUITE DRY SUBSIDENT FLOW. ATLANTIC OCEAN... TODAY TWO MAJOR HURRICANES ARE PRESENT SIMULTANEOUSLY IN THE TROPICAL NORTH ATLANTIC WITH CAT 4 IGOR AND CAT 4 JULIA...QUITE A RARE EVENT. AWAY FROM THESE CYCLONES...WINDS ARE RELATIVELY LIGHT AS THE TYPICAL BERMUDA-AZORES HIGH IS QUITE WEAKENED AND DISPLACED NORTHEASTWARD COMPARED WITH TYPICAL CONDITIONS. THE ONLY MINOR SYNOPTIC FEATURE OF NOTE IS THE TAIL END OF A STATIONARY FRONTAL BOUNDARY 30N57W TO 32N53W AND NORTHEASTWARD FROM THERE. NO DEEP CONVECTION IS FOUND IN ASSOCIATION WITH THIS BOUNDARY...THOUGH THERE MAY BE SOME LOW-TOPPED SHOWERS PRESENT WITHIN 30 NM OF THE AXIS. IN THE UPPER LEVELS...AN UPPER HIGH IS NEAR 19N48W TO THE EAST OF IGOR. THIS...ALONG WITH RIDGING EXTENDING FROM WEST AFRICA ALONG 20N...IS PRODUCING NORTHEASTERLY FLOW THROUGHOUT THE REGION IN THE UPPER LEVELS. IT IS OF INTEREST THAT THE VERY LARGE AND STRONG HURRICANE IGOR IS PRODUCING UPPER LEVEL CYCLONIC FLOW DISCERNIBLE ON THE SYNOPTIC SCALE BEFORE THIS OUTFLOW TURNS ANTICYCLONIC FARTHER FROM THE SYSTEM. ADDITIONALLY...AN UPPER LOW IS DIGGING SOUTHWARD TO THE NORTHWEST OF HURRICANE JULIA AND IS CURRENTLY NEAR 20N37W. WHILE THIS UPPER FEATURE THUS FAR MAY HAVE ASSISTED THE OUTFLOW OF JULIA...IT IS POSSIBLE THAT THE SOUTHWESTERLY WINDS ASSOCIATED WITH THE TROUGH MAY BEGIN TO CAUSE SOME DISRUPTIVE VERTICAL SHEAR IN THE NEXT DAY OR TWO OVER THE HURRICANE. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ LANDSEA