000 AXNT20 KNHC 202359 CCA TWDAT TROPICAL WEATHER DISCUSSION...CATEGORY 4 HURRICANE NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT MON AUG 20 2007 TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN 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...METEOROLOGICAL ANALYSIS... WEATHER OBSERVATIONS...AND RADAR. BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2245 UTC. ...SPECIAL FEATURE... HURRICANE DEAN IS CENTERED NEAR 18.2N 85.1W...OR 180 NM E OF CHETUMAL MEXICO AT 21/0000 UTC MOVING W AT 17 KT. MAXIMUM SUSTAINED WIND SPEED IS 135 KT WITH GUSTS TO 165 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 915 MB. PLEASE SEE THE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC AND THE LATEST PUBLIC ADVISORY UNDER MIATCPAT4/WTNT34 KNHC FOR MORE DETAILS. THIS IS A POWERFUL CATEGORY 4 HURRICANE BORDERING ON A CATEGORY 5 HURRICANE AND BE STILL BECOME A CATEGORY 5 OVER THE NEXT FEW HOURS. DEAN IS EXPECTED TO MAKE LANDFALL OVER THE YUCATAN PENINSULA TUESDAY MORNING. DEAN HAS A SMALL WELL-DEFINED EYE WITH SCATTERED STRONG CONVECTION SURROUNDING THE EYE WITHIN 90 NM IN THE NW SEMICIRCLE AND WITHIN 120 NM IN THE SE SEMICIRCLE. SCATTERED/NUMEROUS THUNDERSTORMS COVER CUBA W OF 77W...ALL OF BELIZE...AND OVER THE YUCATAN PENINSULA E OF 89W. SCATTERED SHOWERS/ISOLATED THUNDERSTORMS DOT THE AREA N OF 13N W OF 76W. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 60W/61W S OF 29N MOVING W 15-20 KT. VERY LARGE AMPLITUDE WAVE WITH UPPER LEVEL WINDS EXPECTED TO GRADUALLY BECOME MORE FAVORABLE FOR DEVELOPMENT DURING THE NEXT COUPLE OF DAYS. SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ARE FROM 19N-26N BETWEEN 50W-62W AND S OF 15N TO INLAND OVER SOUTH AMERICA BETWEEN 55W-63W INCLUDING THE WINDWARD ISLANDS. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 13N15W 8N40W 13N57W. SCATTERED STRONG CONVECTION IS FROM 9N-12N BETWEEN 37W-42W. SCATTERED THUNDERSTORMS DOT THE AREA FROM 3N-10N BETWEEN 28W-54W. CONVECTION W OF 55W IS ASSOCIATED WITH THE TROPICAL WAVE. DISCUSSION... GULF OF MEXICO... AN UPPER LOW IS OVER THE W GULF CENTERED NEAR 27N95W COVERING THE W GULF N OF 20N W OF 90W GENERATING SCATTERED SHOWERS/ ISOLATED THUNDERSTORMS FROM 24N-28N W OF 90W TO INLAND OVER S TEXAS AND NE MEXICO. BROAD UPPER HIGH IN THE W ATLC EXTENDS OVER THE E GULF WHILE THE FAR SE GULF IS UNDER THE INFLUENCE OF HURRICANE DEAN. SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ARE MOVING OFF CUBA AND THROUGH THE YUCATAN CHANNEL AS HURRICANE DEAN CONTINUES TOWARD THE YUCATAN PENINSULA. THERE ARE SOME LOW LEVEL ISOLATED SHOWERS AND POSSIBLE THUNDERSTORMS STREAMING N OVER THE N GULF COAST W OF PANAMA CITY FLORIDA AND OVER S FLORIDA S OF LAKE OKEECHOBEE WHILE THE REMAINDER OF THE GULF REMAINS CLEAR THIS EVENING. HOWEVER...CONDITIONS OVER THE S GULF WILL BEGIN TO DETERIORATE OVERNIGHT AND CONTINUE OVER THE NEXT COUPLE OF DAYS AS DEAN MOVES ACROSS THE YUCATAN PENINSULA INTO THE BAY OF CAMPECHE AND OVER MEXICO ON WEDNESDAY. CARIBBEAN SEA... THE MAIN FOCUS THIS EVENING REMAINS ON THE POWERFUL HURRICANE DEAN. DEAN WILL CONTINUE TO HAVE SIGNIFICANT IMPACTS ON THE W CARIBBEAN OVER THE NEXT DAY OR SO. BROAD UPPER HIGH IS OVER DEAN GIVING UPPER LEVEL OUTFLOW COVERING ALL OF THE W CARIBBEAN INTO THE SE GULF OF MEXICO TO OVER CENTRAL AMERICA. SEE SPECIAL FEATURE ABOVE FOR ASSOCIATED CONVECTION. AN ELONGATED UPPER LOW IS CENTERED JUST S OF PUERTO RICO NEAR 17N66W EXTENDING E/W FROM OVER THE LEEWARD ISLANDS TO OVER HAITI GENERATING CLUSTERS OF SCATTERED SHOWERS/ISOLATED THUNDERSTORMS N OF 17N FROM THE VIRGIN ISLANDS TO HAITI. BROKEN/OVERCAST HIGH CLOUDS ARE STREAMING AWAY FROM HURRICANE DEAN ACROSS THE SE CARIBBEAN. ANOTHER CONCERN THIS EVENING IS THE TROPICAL WAVE JUST MOVING ACROSS THE LESSER ANTILLES...SEE TROPICAL WAVES ABOVE. ATLANTIC OCEAN... BROAD UPPER HIGH IS OVER THE W ATLC CENTERED NEAR 30N76W COVERING THE AREA W OF 70W AND EXTENDING INTO THE E GULF OF MEXICO. DRY...SOMEWHAT STABLE AIR COVERS THE W ATLC W OF 68W WITH SOME LOW LEVEL ISOLATED SHOWERS/THUNDERSTORMS BROUGHT IN BY MODERATE EASTERLY SURFACE FLOW. AN UPPER TROUGH EXTENDS FROM THE UPPER LOW JUST S OF PUERTO RICO TO NEAR 27N62W. THE TROPICAL WAVE IS BENEATH THIS UPPER TROUGH ENHANCING SHOWERS/ THUNDERSTORMS ASSOCIATED WITH THE TROPICAL WAVE. A SECOND UPPER HIGH TO THE E NEAR 25N53W COVERING THE AREA FROM 46W-56W. A BENIGN UPPER LOW IS NEAR 31N32W WHILE TYPICAL UPPER RIDGING EXTENDS E FROM AFRICA OUT TO 25W. LARGE SURFACE RIDGE COVERS THE ATLC EXTENDING FROM A SURFACE HIGH N OF THE AZORES SW THROUGH 32N45W TO A 1023 MB HIGH NEAR 33N73W ACROSS THE SE US AND NE GULF OF MEXICO. ALL OF THIS IS PRODUCING ABUNDANT STABLE CONDITIONS AND MODERATE TRADE WINDS ACROSS THE ATLC WITH THE EXCEPTION OF THE AREA ASSOCIATED WITH THE TROPICAL WAVE. $$ WALLACE