000 AXNT20 KNHC 260005 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT WED SEP 25 2013 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...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS. BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 2315 UTC. ...TROPICAL WAVES... A WEAK TROPICAL WAVE AXIS EXTENDS FROM 18N39W TO 09N36W MOVING WEST NEAR 15 KT. TOTAL PRECIPITABLE WATER AND WATER VAPOR IMAGERY SHOW THE WAVE IS EMBEDDED IN A MODERATE MOIST ENVIRONMENT. GLOBAL MODEL GUIDANCE SUGGEST A WAVE AXIS AT 700 MB HOWEVER LATEST PASSES OF ASCAT AND OSCAT REFLECT NO WAVE SIGNAL AT THE SURFACE. IN THE NORTHERN SECTOR OF THE WAVE THERE IS SOME SAHARAN DRY AIR INHIBITING CONVECTION WHILE SCATTERED MODERATE CONVECTION IS FROM 08N-13N BETWEEN 33W-40W. HOWEVER THIS PRECIPITATION APPEARS TO BE TRAILING CONVECTION FROM THE TROPICAL WAVE AHEAD OF IT. A TROPICAL WAVE AXIS EXTENDS FROM 18N51W TO 10N47W AND MOVES WEST NEAR 15 KT. TOTAL PRECIPITABLE WATER OR TPW IMAGERY SHOW THE WAVE IS EMBEDDED IN A MODERATE TO HIGH MOIST ENVIRONMENT. A CLUSTER OF MODERATE CONVECTION IS IN THE SOUTHERN SECTOR OF THE WAVE FROM 09N-12N BETWEEN 44W-47W...COINCIDING WITH A REGION OF MAXIMUM MOISTURE IN THE TPW. SCATTERED MODERATE CONVECTION IS ELSEWHERE FROM 09N-18N BETWEEN 40W-49W. THIS CONVECTION IS BEING SUPPORTED BY AN UPPER-LEVEL LOW CENTERED NEAR 20N50W AND LOW VALUES OF DEEP LAYER ENVIRONMENTAL WIND SHEAR. A TROPICAL WAVE AXIS EXTENDS FROM 21N58W TO 14N59W AND MOVES W- NW NEAR 15 KT. TOTAL PRECIPITABLE WATER AND WATER VAPOR IMAGERY SHOW THE WAVE CONTINUES EMBEDDED IN A VERY DRY AIR ENVIRONMENT WHICH IS SUPPRESSING CONVECTION. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH AXIS PASSES THROUGH WEST AFRICA NEAR 09N13W TO 07N26W. THE ITCZ CONTINUES FROM 07N26W TO 09N40W TO 05N49W. SCATTERED MODERATE CONVECTION IS FROM 04N-11N BETWEEN 16W-22W. ...DISCUSSION... GULF OF MEXICO... AN UPPER LEVEL TROUGH AXIS EXTENDS FROM OVER THE SE CONUS SW TO A BROAD BASE OVER THE WESTERN GULF. WATER VAPOR IMAGERY INDICATES THIS TROUGH AXIS DELINEATES A MOIST AND DIFFLUENT ATMOSPHERE TO THE EAST AND VERY DRY AND SUBSIDENT ATMOSPHERE TO THE WEST. THIS UPPER LEVEL TROUGH SUPPORTS A 1008 MB LOW CENTERED NEAR 27N91W WITH A SURFACE TROUGH ANALYZED FROM 28N86W TO THE LOW TO 25N94W. A STATIONARY FRONT EXTENDS EAST FROM A 1007 MB LOW OVER THE FLORIDA PANHANDLE TO A 1006 MB LOW OVER THE SW NORTH ATLC REGION NEAR 30N76W. A COLD FRONT EXTENDS SW FROM THE LOW OVER THE FLORIDA PANHANDLE TO 28N90W 27N95W. SCATTERED SHOWERS AND ISOLATED TSTMS ARE OCCURRING ACROSS THE EASTERN GULF WATERS FROM 25N-29N EAST OF 86W AS WELL AS IN PORTIONS OF THE NORTHERN FLORIDA PENINSULA CLOSER TO THE FRONTAL BOUNDARY. ISOLATED SHOWERS REMNANTS OF A SURFACE TROUGH PREVIOUSLY OVER THE BAY OF CAMPECHE ARE SOUTH OF 22N EAST OF 95W. WITHIN A 24 HOUR PERIOD...THE COLD FRONT WILL OVERTAKE THE SURFACE TROUGH AND THEN WILL CONTINUE TO MOVE SE AS A HIGH PRESSURE CENTER DEVELOPS IN THE NW GULF. THE COLD FRONT IS EXPECTED TO MOVE ACROSS SOUTHERN FLORIDA BY FRIDAY AFTERNOON AND BE OFF GULF WATERS EARLY ON SATURDAY. CARIBBEAN SEA... EXCEPT FOR THE SOUTHERN CARIBBEAN...THE WINDWARD PASSAGE AND SOUTHERN CUBA...DRY AIR SUBSIDENCE DOMINATES ACROSS THE BASIN SUPPORTING FAIR WEATHER. AN UPPER LEVEL ANTICYCLONE IS CENTERED OVER THE BAHAMAS IN THE SW NORTH ATLC AND IS PROVIDING MUCH OF THE CENTRAL AND WESTERN CARIBBEAN WITH NORTHEASTERLY FLOW ALOFT. IN THE SW CARIBBEAN...AN INVERTED TROUGH IS NOTED ON WATER VAPOR IMAGERY. GIVEN THE LOW-LEVEL MOISTURE CONVERGENCE DUE TO EASTERLY TRADES AND THE UPPER LEVEL LIFTING DYNAMICS ...SCATTERED MODERATE CONVECTION AND TSTMS ARE OCCURRING S OF 14N WEST OF 78W AND S OF 11N EAST OF 78W. THIS CONVECTION LIKELY ENHANCED DUE TO THE CLOSE PROXIMITY OF THE MONSOON TROUGH AXIS EXTENDS INLAND PANAMA...COSTA RICA...AND CENTRAL NICARAGUA. ISOLATED SHOWERS AND TSTMS ARE JUST WEST OF JAMAICA FROM 17N-19N EAST OF 80W. A TROPICAL WAVE IS EXPECTED TO MOVE ACROSS THE LESSER ANTILLES BY EARLY SATURDAY POSSIBLY ENHANCING SHOWERS IN THE EASTERN CARIBBEAN. HISPANIOLA... CURRENTLY DRY AIR IS ACROSS THE EASTERN ISLAND SUPPORTING FAIR WEATHER. HOWEVER...MODERATE MOISTURE IN THE WINDWARD PASSAGE ALONG WITH A SECTOR OF MIDDLE-LEVEL DIFFLUENCE IN THE SAME REGION IS SUPPORTING SHOWERS AND TSTMS OVER CENTRAL HAITI. IN THE DAYS AHEAD...THE SOUTHERN EXTENT OF A WEAK TROPICAL WAVE CURRENTLY ALONG 58W IS FORECAST TO CLIP ACROSS THE ISLAND SATURDAY PROVIDING A POSSIBLE SLIGHT INCREASE IN CONVECTION DURING THE AFTERNOON AND EVENING HOURS. ATLANTIC OCEAN... OVER THE SW NORTH ATLC...A STATIONARY FRONT EXTENDS WESTWARD FROM A 1007 MB LOW NEAR 30N76W. A WARM FRONT EXTENDS EASTWARD FROM THE LOW TO 29N68W WHERE IT TRANSITIONS TO A COLD FRONT NE TO 30N60W. A PRE-FRONTAL TROUGH EXTENDS FROM 29N62W TO 25N67W. SCATTERED SHOWERS ASSOCIATED WITH THESE FEATURES ARE N OF 23N WEST OF 62W. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ NR