000 AXNT20 KNHC 212342 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT FRI AUG 21 2015 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. ...SPECIAL FEATURES... HURRICANE DANNY CENTERED NEAR 14.5N 49.1W AT 21/2100 UTC OR 860 NM E OF THE LEEWARD ISLANDS MOVING WNW AT 9 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 974 MB. MAXIMUM SUSTAINED WIND SPEED IS 100 KT WITH GUSTS TO 120 KT. SCATTERED MODERATE TO STRONG CONVECTION IS WITHIN 75 NM OF THE CENTER WITH SCATTERED MODERATE CONVECTION ELSEWHERE WITHIN 180 NM IN THE N QUADRANT OF THE CENTER. DANNY HAS LIKELY REACHED ITS PEAK INTENSITY AND THE OFFICIAL FORECAST HAS DANNY WEAKENING THROUGH THE FORECAST PERIOD...WITH A TROPICAL STORM STATUS EXPECTED BY 48 HOURS. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS. ...TROPICAL WAVES... A TROPICAL WAVE HAS EMERGED FROM THE W COAST OF AFRICA WITH AN AXIS EXTENDING FROM 18N21W TO 08N20W MOVING W AT AROUND 10 KT. SAHARAN DRY AIR IS LOCATED MAINLY N OF THE WAVE AXIS WHICH HAS ALLOWED FOR SOME ISOLATED TO WIDELY SCATTERED MODERATE CONVECTION FROM 12N-16N BETWEEN 17W-21W...AND ALSO FROM 06N-10W BETWEEN 16W-26W. THE WAVE COINCIDES WITH AN 850 MB VORTICITY MAXIMUM FROM 12N-15N BETWEEN 17W-23W WHILE THE 700 MB TROUGH AXIS IS NOTED JUST OUT AHEAD OF THE WAVE. A TROPICAL WAVE AXIS EXTENDS FROM 21N33W TO 05N33W AND IS MOVING W AROUND 10-15 KT. THIS WAVE IS EMBEDDED IN SAHARAN DRY AIR AND STABLE CONDITIONS WHICH IS INHIBITING CONVECTION WITH NOT EVEN ISOLATED SHOWERS EVIDENT NEAR THE WAVE AXIS. WEAK VORTICITY IS NOTED FROM 13N-21W ALONG THE WAVE AXIS AND THE 700 MB TROUGH AXIS IS NOTED JUST OUT AHEAD OF THE NORTHERN PORTION OF THE WAVE. A TROPICAL WAVE IS MOVING FROM THE CENTRAL TO THE W CARIBBEAN WITH AN AXIS EXTENDING FROM CENTRAL JAMAICA NEAR 18N77W TO JUST NW OF THE COAST OF COLOMBIA NEAR 10N77W MOVING W AT AROUND 15-20 KT. THE WAVE IS ENCOUNTERING DRY AND STABLE AIR ALOFT WITH NO DIRECTLY ASSOCIATED CONVECTION PRESENT. WEAK 850 MB VORTICITY MAXIMUM IS NOTED ALONG THE WAVE AXIS WHILE A 700 MB TROUGH IS EVIDENT JUST W OF THE TROPICAL WAVE AXIS. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH AXIS EXTENDS FROM THE W COAST OF AFRICA NEAR 14N17W TO 07N27W TO 09N41W. NO WELL DEFINED ITCZ AXIS IS NOTED AT THIS TIME MAINLY DUE TO THE PRESENCE OF HURRICANE DANNY. ISOLATED TO SCATTERED MODERATE CONVECTION IS FROM 05N-07N BETWEEN 26W-31W. ...DISCUSSION... GULF OF MEXICO... AN UPPER LEVEL RIDGE EXTENDS ACROSS THE NORTHERN PART OF THE GULF FROM 29N83W TO THE SW-W TO NEAR 25N96W. AN UPPER LEVEL CYCLONE IS PRESENT OVER THE YUCATAN PENINSULA NEAR 19N90W. ISOLATED CONVECTION IS OCCURRING AROUND THE PERIPHERY OF BOTH UPPER LEVEL FEATURES WITH NO SIGNIFICANTLY ORGANIZED CONVECTION. LIGHT AND VARIABLE ANTICYCLONIC WINDS AND 1-3 FT SEAS WILL PERSIST ACROSS THE NE HALF OF THE GULF...WITH MODERATE TO LOCALLY FRESH SE RETURN FLOW AND 3-6 FT SEAS ACROSS THE SW HALF OF THE GULF. THE STRONGEST WINDS ARE EXPECTED NW-N OF THE YUCATAN PENINSULA DURING THE EVENING AND OVERNIGHT HOURS AS DIURNAL TROUGHING DEVELOPS OVER THE PENINSULA EACH AFTERNOON BEFORE MOVING TO THE W OFFSHORE INTO THE SW GULF WHERE IT WILL DISSIPATE BY SUNRISE EACH DAY. THESE CONDITIONS ARE FORECAST TO PERSIST THROUGH THE NEXT 48 HOURS. CARIBBEAN SEA... AN UPPER LEVEL CYCLONE IS LOCATED OVER THE YUCATAN PENINSULA NEAR 19N90W WHILE AN UPPER LEVEL ANTICYCLONE IS LOCATED OVER THE SW CARIBBEAN NEAR 11N78W. W OF 72W...ONLY ISOLATED CONVECTIVE ACTIVITY IS OCCURRING AROUND THE PERIPHERY OF BOTH OF THESE FEATURES. E OF 72W...UPPER LEVEL TROUGHING IS SHIFTING S SLIGHTLY INTO THE NE PART OF THE BASIN EXTENDING FROM 18N63W TO ACROSS HISPANIOLA. MAINLY DRY AND STABLE AIR IS EVIDENT ON WATER VAPOR SATELLITE IMAGERY. MAINLY MODERATE TO LOCALLY FRESH TRADES AND 3-6 FT SEAS WILL PREVAIL ACROSS THE BASIN THROUGH THE WEEKEND...EXCEPT IN THE S CENTRAL CARIBBEAN WHERE THE PRES GRADIENT WILL BE TIGHT ENOUGH TO SUPPORT OCCASIONAL WINDS TO 20- 25 KT WHICH WILL BUILD SEAS TO 7-9 FT. ...HISPANIOLA... SHALLOW LOW TO MID LEVEL MOISTURE COMBINED WITH DAYTIME HEATING AND OROGRAPHIC LIFTING HAS RESULTED IN ISOLATED SHOWERS AND TSTMS ACROSS THE ISLAND DURING THE AFTERNOON INTO THE EARLY EVENING HOURS. THIS CONVECTIVE ACTIVITY SHOULD DIMINISH SHORTLY AFTER SUNSET WITH THE LOSS OF DAYTIME HEATING. SIMILAR DEVELOPMENT OF SHOWERS AND TSTMS IS POSSIBLE THROUGH THE WEEKEND WITH LITTLE CHANGE IN ATMOSPHERIC CONDITIONS ANTICIPATED. ATLANTIC OCEAN... AN UPPER LEVEL ANTICYCLONE IS LOCATED JUST E OF NORTHERN FLORIDA NEAR 29N80W. AN UPPER LEVEL CYCLONE IS JUST N OF THE DISCUSSION WATERS NEAR 34N66W WITH A TRAILING UPPER TROUGH EXTENDING S-SW THROUGH 30N64W TO 26N76W. THE UPPER CYCLONE AND TROUGH ARE SUPPORTING A 1012 MB LOW NEAR 29N63W WITH A SURFACE TROUGH EXTENDING FROM 32N62W TO THE LOW TO THE SW-W TO 27N73W. SCATTERED SHOWERS AND TSTMS ARE OCCURRING WITHIN 180-210 NM AHEAD OF THE SURFACE TROUGHING. THE LOW IS FORECAST TO MOVE TO THE NW REACHING 33N67W IN 24 HOURS. LIGHT AND VARIABLE WINDS WILL PERSIST ACROSS THE ENTIRE SW N ATLC OFFSHORE WATERS BASIN THROUGH THE NEXT 48 HOURS. SEAS OF 3 FT OR LESS ARE EXPECTED W OF 70W...WITH 3-5 FT SEAS E OF 70W. A 1017 MB SURFACE LOW IS LOCATED OVER THE CENTRAL ATLC NEAR 29N46W WITH A WEAK SURFACE TROUGH ACCOMPANYING IT. THE LOW IS FORECAST TO DISSIPATE BY 24 HOURS AS RIDGING NE OF THE AREA BUILDS SOUTHWESTWARD. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ LEWITSKY