000 AXNT20 KNHC 140003 TWDAT TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT MON OCT 13 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC. ...SPECIAL FEATURES... TROPICAL DEPRESSION NANA IS CENTERED NEAR 17.5N 40.6W AT 13/2100 UTC OR ABOUT 960 NM WEST OF THE CAPE VERDE ISLANDS MOVING WNW AT 8 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1007 MB. MAXIMUM SUSTAINED WIND SPEED IS 30 KT WITH GUSTS TO 40 KT. PLEASE SEE LATEST NHC PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT4/ WTNT34 KNHC AND THE FULL FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS. WESTERLY SHEAR HAS DECREASED CONVECTION NEAR NANA AS THE SYSTEM CONTINUES TO WEAKEN THIS EVENING. SCATTERED MODERATE CONVECTION IS WITHIN 90 NM OF THE CENTER IN THE NE QUADRANT. ELSEWHERE SCATTERED MODERATE CONVECTION IS SE OF THE CENTER FROM 13N-17N BETWEEN 36W-39W. NANA IS FORECAST TO WEAKEN INTO A REMNANT LOW TONIGHT OR TUESDAY. TROPICAL DEPRESSION FIFTEEN IS CENTERED NEAR 14.5N 69.4W AT 14/0000 UTC OR ABOUT 310 NM SW OF SAN JUAN PUERTO RICO REMAINING NEARLY STATIONARY. LITTLE MOTION IS EXPECTED DURING THE NEXT 24 HOURS. HOWEVER...A NE MOTION IS FORECAST TO BEGIN ON LATE TUESDAY OR EARLY WEDNESDAY BRINGING THE CYCLONE VERY CLOSE TO PUERTO RICO OR THE VIRGIN ISLANDS. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1001 MB. MAXIMUM SUSTAINED WIND SPEED IS 30 KT WITH GUSTS TO 40 KT. PLEASE SEE LATEST NHC PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT5/WTNT35 KNHC AND THE FULL FORECAST/ ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT5/WTNT25 KNHC FOR MORE DETAILS. NUMEROUS MODERATE/STRONG CONVECTION IS LOCATED WITHIN 160 NM OF THE CENTER IN THE ERN SEMICIRCLE. SCATTERED MODERATE/ ISOLATED STRONG CONVECTION IS LOCATED FROM 12N-19N BETWEEN 60W-70W. A 1006 MB LOW PRESSURE IS IN THE WRN CARIBBEAN SEA NEAR 14N82W...A SHORT DISTANCE EAST OF THE COAST OF NICARAGUA. THIS LOW IS ACCOMPANIED BY A LARGE AREA OF DISTURBED WEATHER WITH SCATTERED MODERATE/ISOLATED STRONG CONVECTION FROM 11N-19N BETWEEN 78W-86W. CONDITIONS APPEAR FAVORABLE FOR ADDITIONAL DEVELOPMENT AND THE SYSTEM COULD BECOME A TROPICAL DEPRESSION DURING THE NEXT COUPLE OF DAYS AS IT MOVES SLOWLY NORTHWESTWARD. ...TROPICAL WAVES... A WEAK TROPICAL WAVE IS ALONG 50W S OF 20N MOVING W NEAR 15 KT. THE WAVE IS EMBEDDED IN AN AREA OF MODERATE TO STRONG SUBSIDENCE KEEPING ANY ASSOCIATED SHOWERS CONFINED TO THE ITCZ ALONG 11N BETWEEN 49W-52W. A TROPICAL WAVE IS ALONG 60W SOUTH OF 20N MOVING WEST NEAR 10 KT. THE WAVE IS QUICKLY BECOMING ABSORBED INTO T.D. FIFTEEN AS IT TRACKS WESTWARD. POSSIBLE SCATTERED SHOWERS ARE ACROSS BARBADOS AND THE CENTRAL LESSER ANTILLES THIS EVENING...BUT MOST OF THIS ACTIVITY IS ATTRIBUTED TO T.D. FIFTEEN AND AN UPPER DIFFLUENT PATTERN ACROSS THE ERN CARIBBEAN SEA. ...THE ITCZ... ITCZ AXIS IS CENTERED ALONG 11N17W 9N30W 12N40W 12N43W 11N49W 10N52W 10N58W. A 1008 MB LOW IS EMBEDDED WITHIN THE ITCZ NEAR 13N42W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 12N-14N BETWEEN 40W-42W IN ASSOCIATION WITH THE SURFACE LOW. ELSEWHERE...SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM 9N-12N BETWEEN 19W-30W. CLUSTERS OF SCATTERED MODERATE CONVECTION ARE FROM 5N-11N BETWEEN 30W-37W. ...DISCUSSION... GULF OF MEXICO... AN UPPER RIDGE EXTENDS OVER ERN TEXAS INTO NE MEXICO PRODUCING DRY NORTHERLY UPPER FLOW AND STABLE ATMOSPHERIC CONDITIONS NW OF A LINE FROM SE LOUISIANA TO NEAR VERACRUZ MEXICO. AN UPPER-LEVEL LOW IS CENTERED IN THE WRN BAY OF CAMPECHE NEAR 20N95W AND CONTINUES MOVING WESTWARD. LOW-LEVEL INSTABILITY AND MOIST SOUTHERLY MID-HIGH LEVEL FLOW TO THE EAST OF THIS FEATURE IS HELPING TO INDUCE SCATTERED SHOWERS AND TSTMS OVER THE CENTRAL AND ERN GULF...INCLUDING THE SRN FLORIDA PENINSULA. THIS ACTIVITY REMAINS S OF 28N AND E OF 92W. A HIGH PRESSURE CENTER OVER THE MID-ATLANTIC STATES DOMINATES THE SE CONUS AND NRN FLORIDA PENINSULA. THE PRESSURE GRADIENT BETWEEN THIS HIGH AND THE BROAD AREA OF LOW PRESSURE ACROSS THE WRN CARIBBEAN SEA IS GENERATING MODERATE TO STRONG ELY WINDS OVER THE ERN GULF. CARIBBEAN SEA... TWO AREAS OF CONCERN ACROSS THE CARIBBEAN SEA...ONE IS T.D. FIFTEEN IN THE ERN CARIBBEAN...AND THE SECOND ONE IS A BROAD AREA OF LOW PRESSURE IN THE WRN CARIBBEAN...SEE SPECIAL FEATURES FOR MORE DETAILS. UPPER LEVEL RIDGING COVERS MUCH OF THE CARIBBEAN WHICH IS AIDING IN GENERATING THE CONVECTIVE ACTIVITY ASSOCIATED WITH T.D. FIFTEEN AND THE AREA OF LOW PRESSURE OVER THE WRN CARIBBEAN. CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION ARE ACROSS THE WRN CARIBBEAN W OF 77W DUE TO A LARGE AREA OF UPPER DIFFLUENCE CREATED FROM THE UPPER LOW OVER THE SW GULF OF MEXICO AND THE RIDGING ACROSS THE WRN CARIBBEAN. MUCH OF THE CONVECTION ASSOCIATED WITH T.D. FIFTEEN REMAINS E OF 71W WITH DEEP LAYERED MOISTURE IN PLACE ACROSS THE CENTRAL AND ERN CARIBBEAN. ATLANTIC OCEAN... T.D. NANA CONTINUES TO MOVE OVER THE OPEN WATERS OF THE TROPICAL ATLC...SEE SPECIAL FEATURES ABOVE. SCATTERED SHOWERS AND TSTMS ARE ACROSS THE FAR W ATLC...NW BAHAMAS AND SRN FLORIDA PENINSULA THIS EVENING FROM 24N-28N W OF 76W. THIS ACTIVITY IS MOVING WWD UNDER EASTERLY SURFACE FLOW AROUND A HIGH PRESSURE SYSTEM LOCATED OVER THE MID-ATLANTIC STATES. A WEAK SURFACE TROUGH... ASSOCIATED WITH BROAD UPPER TROUGHING ACROSS THE W ATLC... EXTENDS INTO THE DISCUSSION AREA NEAR 32N47W TO 27N51W. ANOTHER SURFACE TROUGH EXTENDS FROM 27N57W TO 24N61W. POSSIBLE SCATTERED SHOWERS ARE WITHIN 150 NM OF BOTH SURFACE TROUGHS ACROSS THE CENTRAL ATLC. A RIDGE ANCHORED ON AN UPPER-LEVEL HIGH NEAR 11N30W DOMINATES THE TROPICS AND IS ENHANCING CONVECTION ALONG THE ITCZ. A SURFACE TROUGH IS ALONG THE W AFRICAN COAST EXTENDING FROM 19N16W TO THE ITCZ AXIS NEAR 11N16W. NO SIGNIFICANT PRECIPITATION IS OBSERVED ON SATELLITE IMAGERY...BUT HOURLY SURFACE OBSERVATIONS SHOW A WIND SHIFT ALONG THE COAST. FURTHER NORTH...A SURFACE RIDGE OF HIGH PRESSURE ANCHORED ON A 1022 MB HIGH CENTERED NEAR 33N28W INFLUENCES THE NE ATLC N OF 20N AND E OF 41W. $$ HUFFMAN