000 AXNT20 KNHC 061107 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 AM EDT SUN APR 06 2008 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1045 UTC. ...THE ITCZ... THE ITCZ AXIS IS CENTERED ALONG 9N13W 4N20W 1N30W...CROSSING THE EQUATOR NEAR 26W...TO THE NORTHEASTERN COAST OF BRAZIL NEAR 6S35W. SCATTERED MODERATE SCATTERED STRONG CONVECTION WITHIN 240 NM N AND 120 NM S OF AXIS BETWEEN 17W AND 24W. SCATTERED MODERATE CONVECTION FROM EQUATOR TO 7N BETWEEN 30W AND 40W. ...DISCUSSION... THE GULF OF MEXICO... A SOUTHERN STREAM SHORTWAVE TROUGH PASSING THROUGH THE SOUTH- EASTERN STATES SUPPORTS A WEAK COLD FRONT ACROSS THE NORTH CENTRAL AND NE GULF OF MEXICO THIS MORNING. WITH THE MAIN UPPER-LEVEL SUPPORT NOW NE OF THE AREA...THE FRONT HAS BECOME NEARLY STATIONARY FROM 30N86W TO A WEAK SURFACE 1011 MB LOW ANALYZED CLOSE TO 29N86W AND THEN EXTENDS SW TO 24N97W AND THEN BARELY INLAND OVER FAR OVER FAR NE MEXICO. EARLIER QUIKSCAT PASSES AND MORE RECENT ASCAT IMAGERY EASILY DEPICTS THE FRONT OVER THE CENTRAL GULF...BUT THE FRONT BECOMES MUCH HARDER TO IDENTIFY OVER THE W CENTRAL GULF...WITH THE ONLY EVIDENCE A BROAD CYCLONIC SHEAR AND A SUBTLE INCREASE TO THE LOW-LEVEL WINDS. MICROWAVE DATA OVER THE EASTERN GULF WAS ALMOST ENTIRELY RAIN-CONTAMINATED AND THUS NOT RELIABLE FOR PLACING THE FRONT...EXCEPT FOR A FEW DATA POINTS IN A 0326 UTC ASCAT PASS. THESE DATA INDICATED A SW TO W 20- TO 30-KT INFLOW INTO A WELL-ORGANIZED CONVECTIVE LINE PROPAGATING WELL AHEAD OF THE FRONT OVER THE EASTERN GULF AND CENTRAL AND NOW SOUTHERN FL. LATEST SURFACE OBS...BUOY...AND CMAN OBSERVATIONS REVEAL A NE-SW ORIENTED OUTFLOW BOUNDARY AT THE LEADING EDGE OF THE CONVECTIVE LINE...MOVING OFFSHORE THE SE FL COAST AND KEYS AS OF 0900 UTC AND FOLLOWED BY A LARGE AREA OF STRATIFORM PRECIPITATION. FOWEY ROCKS LIGHT REPORTED A NW 40-KT WIND IMMEDIATELY AFTER ITS PASSAGE AND A LARGE PRESSURE SPIKE...WITH SURFACE OBSERVATIONS OVER SOUTHERN FL SUGGESTING A WELL-DEFINED MESO-HIGH IN THE CONVECTIONS WAKE. ELSEWHERE SE OF THE FRONT...NEW CONVECTION IS DEVELOPING WITHIN 90 NM SE OF THE BOUNDARY BETWEEN 26N AND THE WEAK SURFACE WAVE. IN FACT...WITHIN THE LAST HOUR...LIGHTNING DATA REVEALS A NEW EXPLOSION OF LIGHTNING STRIKES WITHIN THIS AREA...LIKELY SIGNALING THE FORMATION OF A NEW CONVECTIVE COMPLEX FOR LATER TODAY. OTHERWISE...A SE TO S WIND FLOW OF 10- TO 15 KT GENERALLY PREVAILS EXCEPT IN THE BAY OF CAMPECHE THE FLOW SHIFTS MORE NE AND THUS MORE CYCLONIC AROUND A MECHANICALLY-FORCED LOW. SKIES REMAIN GENERALLY CLOUD-FREE TOO...EXCEPT FOR SCATTERED LOW CLOUDS OVER THE S CENTRAL AND SW GULF. W OF THE FRONT...SURFACE RIDGING IS NOTED FROM THE UPPER TX AND SW LOUISIANA COASTS INTO NE MEXICO...WITH SCATTERED STRATUS CLOUDS ACROSS THE AREA. SHORT-MODEL GUIDANCE INDICATES THAT THE SE U.S. SHORTWAVE SHOULD LIFT OUT TODAY...UNABLE TO DIG FURTHER THANKS TO A SOLID AREA OF MID-LEVEL RIDGING PARKED OVER THE WESTERN ATLANTIC. WITH THE MAIN UPPER-LEVEL DYNAMICS SHIFTING NORTHWARD ...EXPECT THE BULK OF THE PRECIPITATION TO FALL FROM GEORGIA THROUGH THE CAROLINAS WITH THE COVERAGE AND INTENSITY GENERALLY DECREASING OVER THE EASTERN GULF AND FLORIDA. HOWEVER...A MOIST LOW-LEVEL FLOW INTERSECTING THE BOUNDARY ALONG WITH A PATTERN OF FAVORABLE DIVERGENCE ALOFT SHOULD BE ENOUGH TO SUPPORT SCATTERED TO LOCALLY NUMEROUS RAIN SHOWERS AND TSTMS ACROSS THE EASTERN GULF AND FL AROUND THE TIME OF PEAK HEATING. NOW THAT THE MAIN UPPER SUPPORT IS ALREADY WELL NE OF THE AREA AND THE MID- TO UPPER- LEVEL FLOW HAS BECOME NEARLY PARALLEL TO THE FRONT...THE FRONT SHOULD REMAIN NEARLY STATIONARY THE NORTHERN GULF AND N FLORIDA ...WITH THE WESTERN END LOSING ITS IDENTITY. THEREAFTER...MODELS INDICATE THAT A SEPARATE AND MUCH WEAKER SOUTHERN STREAM SHORTWAVE RACING THROUGH THE NE GULF SUN EVENING SHOULD SPARK THE DEVELOPMENT OF A NEW WAVE ALONG THE FRONT OVER THE NE GULF...WHICH SHOULD TRACK ACROSS N FLORIDA AND EMERGE INTO THE ATLANTIC WATERS AND EVENTUALLY DRAG THROUGH THE FRONT DOWN THE STATE OF FL MON. CARIBBEAN SEA... WATER VAPOR REVEALS HIGH-LEVEL WESTERLY FLOW DOMINATING MUCH OF THE BASIN...WITH THE REMAINS OF A WEAKENING UPPER-LEVEL TROUGH LYING FROM 19N80W TO 9N85W. MODERATE TO STRONG UPPER SUBSIDENCE ASSOCIATED WITH A LARGE AND DOMINANT MID- TO UPPER-LEVEL ANTICYCLONE IN THE TROPICAL E PACIFIC CONTINUES TO BE OBSERVED AS FAR E AS THE WESTERN CARIBBEAN W OF THE DISSIPATING TROUGH AXIS. LIKE YESTERDAY...A PLUME OF MOISTURE WITH ORIGINS FROM CONVECTIVE DEBRIS OVER THE AMAZON IS BEING DRAWN NORTHWARD FROM NORTHERN COLOMBIA TO JUST SOUTH OF HISPANIOLA AND PUERTO RICO. DESPITE THE SUBTLE INCREASE IN UPPER TROPOSPHERIC MOISTURE AND SLIGHTLY DIFFLUENT UPPER-LEVEL FLOW...LITTLE IN THE WAY OF CONVECTION IS NOTED EXCEPT OVER NORTHERN COLOMBIA YESTERDAY EVENING. IN FACT...THE ONLY CONVECTION OF CONSEQUENCE WAS OVER CUBA LATE YESTERDAY...WHERE LOCAL SEA BREEZE CIRCULATIONS AND A GRADUALLY DESTABILIZING ATMOSPHERE LED TO LATE AFTERNOON TSTMS. OTHERWISE...A 1026 MB SURFACE HIGH PRESSURE OVER THE CENTRAL ATLANTIC NEAR NEAR 29N62W HAS AN EXTENSION INTO THE CARIBBEAN SEA AND IS PROVIDING A CONTINUED FRESH TRADE WIND FLOW ACROSS THE EASTERN AND CENTRAL PART OF THE BASIN. HOWEVER...COMPARED TO EARLY YESTERDAY...TRADES ARE SLIGHTLY WEAKER AND ARE CLOSER TO CLIMATOLOGICAL AVERAGES AS SUGGESTED BY SOME OF THE REAL-TIME NCEP RE-ANALYSIS DATA. ELSEWHERE...ASCAT AND HIGH RESOLUTION QUIKSCAT OVERNIGHT INDICATED STRONG E TO SE 25-KT WINDS OVER THE GULF OF HONDURAS...AND RECENT SURFACE OBSERVATIONS SHOW A WEAK SURFACE LOW ALONG THE NORTHERN HONDURAN COAST NEAR 16N87W. THIS FEATURE AND THE DEVELOPMENT OF THESE STRONG WINDS COULD BE A CONSEQUENCE OF WHATEVER CONVECTIVE OUTFLOW PUSHED OFF THE YUCATAN PENINSULA LATE LAST NIGHT AND EARLY THIS MORNING. OVER THE NEXT FEW DAYS...A WELL-DEFINED MID- TO UPPER-LEVEL RIDGE SHOULD CONTINUE TO PREVAIL N OF THE CARIBBEAN IN THE VICINITY OF 25N60W. THIS SHOULD ALLOW FOR A PATTERN OF WEAKER- THAN-NORMAL WESTERLY FLOW AT UPPER LEVELS ACROSS THE REGION... WITH NOTABLE EASTERLY WIND ANOMALIES LIKELY THROUGH THE WEEKEND INTO EARLY NEXT WEEK. MEANWHILE...THE SURFACE RIDGE OVER THE CENTRAL ATLANTIC SHOULD GRADUALLY WEAKEN WHILE SHIFTING SSE... WHICH SHOULD CAUSE THE FRESH TRADE WIND FLOW ACROSS THE AREA TO RELAX. ATLANTIC OCEAN.... AN ANOMALOUSLY STRONG MID-LEVEL RIDGE REMAINS LOCKED IN PLACE OVER THE WEST CENTRAL ATLANTIC NEAR 25N60W...DIRECTING THE STRONG MID-LATITUDE FLOW OVER THE EASTERN CONUS N OF THE AREA. INSTEAD THE STRONGER MID-LATITUDE FLOW DIGS EASTWARD INTO A BROAD...DEEP-LAYERED TROUGH W OF 50 AND N OF ABOUT 15N...WITH AN ASSOCIATED CLOSED CYCLONIC CIRCULATION NEAR 37N30W. AT THE LEADING EDGE OF THE TROUGH LIES A SURFACE COLD FRONT EXTENDING FROM 31N21W TO 21N37W FOLLOWED BY A LARGE DOME OF SURFACE HIGH PRESSURE CENTERED NEAR 29N62W. THE STRONG PRESSURE GRADIENT BETWEEN THE HIGH AND THE LOWER LATITUDES IS RESULTING IN NORMAL TO ENHANCED TRADES...MOSTLY OVER THE AREA S OF 20N AND W OF 45W TO THE LESSER ANTILLES. IN FACT...EARLIER QUIKSCAT PASSES REVEALED STILL 20- TO 25-KT NE WINDS OVER MUCH OF THE ABOVE AREA...WITH SEAS GENERALLY 9 TO 12 FT IN NE SWELL. WITH THE SURFACE RIDGE FORECAST TO GRADUALLY WEAKEN AND SHIFT SSE...THE FRESH TRADES SHOULD RELAX GOING INTO EARLY NEXT WEEK...WITH SEAS SUBSIDING TO 6 TO 8 FT BY TUE NEXT WEEK. W OF 50W...A BROAD SURFACE CYCLONIC FLOW COVERS THE AREA N OF ABOUT 25N...DIRECTLY BEHIND A COLD FRONT MOVING E OF THE AREA. OTHER THAN A FAIRLY THICK DECK OF STRATOCUMULUS W OF THE FRONT ...THERE IS LITTLE ELSE THAT DEFINES THIS FEATURE. AS THE FRONT RACES FARTHER SE TODAY...A NEW INJECTION OF COOLER AIR SHOULD BRIEFLY RE-INVIGORATE THE LARGE CYCLONIC CENTER S OF THE AZORES. THIS...IN TURN...SHOULD KEEP THE CURRENT DEEP-LAYERED CYCLONIC FLOW OVER THE AREA IN PLACE INTO EARLY NEXT WEEK. ELSEWHERE...WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS INDICATE A NARROW MID- TO UPPER-LEVEL RIDGE S OF ABOUT 12N FROM THE NW COAST OF AFRICA TO JUST SE OF THE WINDWARD ISLANDS. THE DEEP EASTERLIES S OF THE RIDGE ALONG WITH THE PRESENCE OF AN EQUATORIAL KELVIN WAVE APPROACHING 0W HAVE BEEN PROVIDING A FAVORABLE ENVIRONMENT FOR ENHANCED CONVECTION ALONG THE ITCZ THE LAST FEW DAYS. THIS PATTERN OF ANOMALOUS EASTERLY FLOW AND ENHANCED CONVECTION SHOULD GRADUALLY DIMINISH BY EARLY NEXT WEEK...ONCE THE KELVIN WAVE PROPAGATES E OF THE AREA. $$ KIMBERLAIN