000 AXNT20 KNHC 271751 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 205 PM EDT MON OCT 27 2008 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. ...TROPICAL WAVES... TROPICAL WAVE IS ALONG 42W S OF 15N MOVING W 10-15 KT. CIMSS WAVETRAK PRODUCT DEPICTS LOW LEVEL CYCLONIC CIRCULATION MAXIMIZED ALONG WAVE AXIS. WAVE IS AT THE LEADING EDGE OF A BROAD WESTWARD-MOVING SURGE IN DEEP LAYER MOISTURE BASED ON TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. SCATTERED MODERATE CONVECTION IS WITHIN 210 NM E OF WAVE AXIS. ALSO...ISOLATED MODERATE CONVECTION IS WITHIN 180 NM W OF WAVE AXIS N OF 10N. TROPICAL WAVE IS ALONG 55W/56W S OF 15N MOVING W 10-15 KT. SURFACE OBSERVATIONS AND A RECENT QUIKSCAT PASS DEPICT CYCLONIC CURVATURE IN SURFACE WIND FIELD NEAR WAVE AXIS. DEEP LAYER DRY AIR WRAPPING AROUND AN UPPER HIGH OVER NW HAITI NEAR 20N73W IS INHIBITING CONVECTION NEAR THE WAVE...THOUGH ISOLATED SHOWERS ARE WITHIN 120 NM E OF WAVE AXIS N OF 13N. ...THE ITCZ... ITCZ AXIS IS ANALYZED ALONG 9N13W 5N26W 7N39W 8N49W 8N60W. ISOLATED MODERATE CONVECTION IS FROM 7N-12N BETWEEN 12W-18W. SCATTERED MODERATE CONVECTION IS FROM 2N-14N BETWEEN 28W-38W... WHICH IS BEING ENHANCED BY STRONG UPPER LEVEL DIFFLUENCE. ISOLATED MODERATE CONVECTION IS FROM 7N-12N BETWEEN 48W-52W. ...DISCUSSION... GULF OF MEXICO... THE LARGE SCALE WEATHER PATTERN OVER THE GULF IS UNDERGOING A SUBSTANTIAL PATTERN CHANGE...AS AN UNUSUALLY STRONG 1042 MB SURFACE HIGH IN THE PLAINS OF THE CONUS BEGINS TO EXERT ITS INFLUENCE OVER THE GULF. AT THE LEADING EDGE OF THE ASSOCIATED MODIFIED CONTINENTAL POLAR AIRMASS IS A STRONG SURFACE COLD FRONT THAT IS SURGING SOUTHWARD NEAR 30 KT ACROSS THE NW GULF. THIS FRONT EXTENDS FROM THE W FLORIDA PANHANDLE NEAR 30N86W TO 28N92W TO S TEXAS NEAR 27N97W. THIS FRONT MARKS A PARTICULARLY STRONG GRADIENT IN LOW LEVEL MOISTURE...AS SURFACE DEWPOINTS RANGE FROM THE 60S IMMEDIATELY AHEAD OF THE FRONT TO THE 20S WITHIN 90 NM BEHIND THE FRONT. ALSO...SURFACE TEMPERATURES RANGE FROM THE 70S IMMEDIATELY AHEAD OF THE FRONT TO THE 50S WITHIN 90 NM BEHIND THE FRONT...WITH INCREASED NORTHERLY SURFACE WINDS BEHIND THE FRONT. THE STRONG GRADIENT IN MOISTURE AND TEMPERATURE ACROSS THE FRONT IS SUPPORTING BANDS OF CLOUDS AND ISOLATED SHOWERS WITHIN 60 NM EITHER SIDE OF THE FRONT. THIS FRONT IS ALSO BEING SUPPORTED BY A DEEP TROUGH OVER THE E CONUS...WITH STRONG MID/UPPER-LEVEL WESTERLY WINDS OVER THE N GULF. RELATIVELY DRY DEEP LAYER AIR COVERS THE GULF IN THE WAKE OF A SURFACE BOUNDARY SE OF THE GULF REGION...WHICH IS RESULTING IN GENERALLY FAIR WEATHER ACROSS MUCH OF THE GULF. ADDITIONALLY...STRONG NE TO E WINDS ARE BLOWING THROUGH THE ISTHMUS OF TEHUANTEPEC RESULTING IN GALE FORCE WINDS IN THE E PACIFIC REGION...WHICH ARE EXPECTED TO INCREASE TO STORM FORCE AT 1200 UTC TUESDAY. CARIBBEAN SEA... AN UPPER LEVEL RIDGE AXIS EXTENDS WESTWARD FROM AN UPPER HIGH OVER NW HAITI NEAR 20N73W TO W GUATEMALA NEAR 17N91W. SOUTHWESTERLY FLOW ALOFT N OF THE UPPER RIDGE CONTINUES TO TRANSPORT DEEP MOISTURE INTO THE NW CARIBBEAN. THIS MOISTURE IS INTERACTING WITH A STATIONARY FRONT THAT EXTENDS FROM MIDWAY BETWEEN THE S FLORIDA PENINSULA NEAR 24N80W TO 20N86W TO THE GULF OF HONDURAS NEAR 16N88W...WHICH IS RESULTING IN SCATTERED MODERATE CONVECTION WITHIN 90 NM EITHER SIDE OF THE SURFACE STATIONARY FRONT. ACROSS THE CENTRAL AND E CARIBBEAN...DEEP LAYER DRY AIR AND SUBSIDENCE S OF THE UPPER HIGH ARE RESULTING IN GENERALLY FAIR WEATHER. HOWEVER...ISOLATED MODERATE CONVECTION IS OCCURRING OVER THE SW CARIBBEAN FROM 8N-11N BETWEEN 76W-81W IN RESPONSE TO WEAK UPPER LEVEL DIVERGENCE INTERACTING WITH DEEP LAYER MOISTURE STREAMING NORTHWESTWARD FROM NW SOUTH AMERICA. ALSO...AN UPPER TROUGH EXTENDS FROM THE ATLC NEAR 24N46W TO THE SE CARIBBEAN NEAR 11N64W...WITH DEEP LAYER DRY AIR EMBEDDED WITHIN THIS TROUGH IN THE SE CARIBBEAN. ATLANTIC OCEAN... A DEEP LAYER TROUGH OVER THE E CONUS IS APPROACHING THE W ATLC...WITH STRONG MID/UPPER LEVEL FLOW ROTATING AROUND THE BASE OF THE TROUGH INTO THE W ATLC. DEEP LAYER DRY AIR EMBEDDED WITHIN THE TROUGH IS RESULTING IN GENERALLY FAIR WEATHER OVER THE W ATLC IN THE WAKE OF A COLD FRONT THAT EXTENDS FROM 32N69W TO 27N74W TO MIDWAY BETWEEN THE S FLORIDA PENINSULA AND N CUBA NEAR 24N80W. DEEP LAYER MOISTURE WRAPPING AROUND THE UPPER HIGH OVER NW HAITI NEAR 20N73W IS SUPPORTING SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WITHIN 60 NM EITHER SIDE OF THE COLD FRONT W OF 77W. A MUCH DRIER AND COOLER AIRMASS WILL BEGIN TO PUSH ACROSS THE W ATLC TONIGHT...WHICH IS BEING USHERED IN BY A COLD FRONT THAT IS CURRENTLY MOVING SOUTHWARD ACROSS CENTRAL GEORGIA...THE W FLORIDA PANHANDLE...AND THE NW GULF OF MEXICO. FURTHER TO THE E...UPPER LEVEL ANTICYCLONIC FLOW ASSOCIATED WITH THE AFOREMENTIONED UPPER HIGH OVER NW HAITI COVERS MUCH OF THE CENTRAL ATLC...AND A DEEP LAYER TROUGH EXTENDS FROM 32N42W TO 24N46W TO THE SE CARIBBEAN NEAR 11N64W. THIS TROUGH IS SUPPORTING A SURFACE TROUGH THAT EXTENDS FROM 31N42W TO 24N46W TO 20N56W. THIS TROUGH IS MARKED BY WEAK SURFACE CONFLUENCE... WITH ISOLATED MODERATE CONVECTION OCCURRING WITHIN 60 NM EITHER SIDE OF THE SURFACE TROUGH. FARTHER TO THE E...AN UPPER RIDGE IS N OF 24N BETWEEN 21W-39W...AND AN UPPER TROUGH IS N OF 19N E OF 17W. GENERALLY DEEP LAYER DRY AIR IS PREVENTING DEEP CONVECTION NEAR THESE FEATURES. ALSO...SUBSIDENCE IS OCCURRING IN THE VICINITY OF A SURFACE RIDGE IN THE E ATLC...WHERE GENERALLY FAIR WEATHER CONDITIONS PREDOMINATE. OVER THE TROPICAL ATLC...AN EAST-TO-WEST UPPER RIDGE IS ALONG 12N BETWEEN THE AFRICAN COAST AND 25W. $$ COHEN