000 AXNT20 KNHC 212347 TWDAT TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 805 PM EDT TUE JUL 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. ...TROPICAL WAVES... TROPICAL WAVE EXTENDS FROM 09N26W TO 17N24W MOVING W AT 15 KT. THE WAVE COINCIDES WITH A VERY BROAD AND SUBTLE 700 MB TROUGH NOTED IN GLOBAL MODEL GUIDANCE BETWEEN 21W-27W. A NARROW AND WEAK AREA OF 850 MB RELATIVE VORTICITY ALSO EXTENDS ACROSS THE WAVE AXIS FROM 14N22W TO 08N35W INDICATING THE STRETCHED OUT NATURE OF THE ENERGY ASSOCIATED WITH THE WAVE. NO SIGNIFICANT DEEP CONVECTION IS OCCURRING WITH THE WAVE AT THIS TIME DUE TO SAHARAN DUST COVERING MUCH OF THE EASTERN TROPICAL ATLC. TROPICAL WAVE EXTENDS FROM 08N62W TO 18N59W MOVING W AT 20 KT. THE WAVE COINCIDES WITH 700 MB TROUGHING ALOFT BETWEEN 57W-64W ON THE SOUTHWESTERN PERIPHERY OF A MID-LEVEL RIDGE CENTERED OVER THE CENTRAL ATLC NEAR 23N52W. SCATTERED MODERATE AND ISOLATED STRONG CONVECTION IS OCCURRING FROM 08N-11N BETWEEN 57W-64W... WITH SCATTERED MODERATE CONVECTION FROM 11N-15N BETWEEN 58W-64W. TROPICAL WAVE EXTENDS FROM OVER NW VENEZUELA NEAR 07N69W TO THE SOUTH COAST OF THE DOMINICAN REPUBLIC NEAR 18N68W MOVING W AT 15- 20 KT. THE WAVE REMAINS EMBEDDED WITHIN A NARROW MAXIMUM OF TOTAL PRECIPITABLE WATER BETWEEN 65W-72W THAT STRETCHES NORTH- NORTHEASTWARD FROM THE WAVE AXIS...FOCUSED ALONG A SURFACE TROUGH EXTENDING FROM 19N68W TO 25N61W. THE MOISTURE THEN EXTENDS INTO THE INFLUENCE OF AN UPPER LEVEL TROUGH AXIS EXTENDING OVER THE CENTRAL ATLC. ISOLATED TO SCATTERED MODERATE CONVECTION IS FROM 11N-17N BETWEEN 66W-72W...WITH MORE CONCENTRATED SCATTERED MODERATE TO STRONG CONVECTION OVER NORTHERN VENEZUELA FROM 07N-11N BETWEEN 64W-72W. TROPICAL WAVE EXTENDS FROM THE NORTHEAST PACIFIC OCEAN AND THE GULF OF PANAMA NEAR 06N80W TO 17N77W MOVING W AT 20-25 KT. THE WAVE COINCIDES WITH VERY BROAD 700 MB TROUGHING BETWEEN 76W-82W AND IS LARGELY INFLUENCED ALOFT BY AN UPPER LEVEL RIDGE CENTERED OVER THE SW CARIBBEAN NEAR 14N80W. ISOLATED MODERATE CONVECTION IS FROM 08N-11N BETWEEN 78W-82W. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH AXIS EXTENDS FROM THE AFRICAN COAST NEAR 14N17W TO 11N20W TO 08N30W. THE INTERTROPICAL CONVERGENCE ZONE AXIS EXTENDS FROM 08N30W TO 05N44W TO 10N58W. ISOLATED TO WIDELY SCATTERED MODERATE CONVECTION IS FROM 09N-11N BETWEEN 19W-22W... AND FOR A GREAT DISTANCE WITHIN 60 NM EITHER SIDE OF THE AXIS BETWEEN 31W-57W. ...DISCUSSION... GULF OF MEXICO... NORTHEAST TO EASTERLY FLOW ALOFT PREVAILS OVER MUCH OF THE GULF THIS EVENING BETWEEN A MIDDLE TO UPPER LEVEL ANTICYCLONIC CIRCULATION CENTERED OVER SOUTH CENTRAL TEXAS NEAR 29N101W AND AN UPPER LEVEL LOW CENTERED OVER THE NORTHERN YUCATAN PENINSULA NEAR 21N88W. WHILE A MAJORITY OF THE BASIN IS UNDER THIS RELATIVELY STABLE FLOW...AT THE SURFACE...WEAK AND ILL-DEFINED TROUGHING AND LOW-LEVEL MOISTURE CONVERGENCE IS PRESENT ACROSS THE NE GULF STEMMING FROM A WEAK STREAM OF 500 MB RELATIVE VORTICITY EXTENDING FROM OVER THE FLORIDA BIG BEND REGION SW TO OVER THE NW GULF NEAR 27N93W. THIS MID-LEVEL VORTICITY IS PROVIDING FOCUS FOR SCATTERED SHOWERS AND ISOLATED TSTMS OCCURRING FROM 26N-30N BETWEEN 83W-92W. OTHERWISE...A SURFACE RIDGE AXIS EXTENDS FROM 1018 MB HIGH PRESSURE IN THE SE GULF NEAR 24N84W TO THE NW ALONG THE TEXAS COAST NEAR 29N96W. GENTLE TO OCCASIONAL MODERATE BREEZE ANTICYCLONIC FLOW IS FORECAST ACROSS THE BASIN THROUGH LATE THURSDAY...EXCEPT NW OF THE YUCATAN PENINSULA WHERE WINDS WILL INCREASE TO 20 KT DURING THE OVERNIGHT HOURS DUE TO DIURNAL TROUGHING WHICH WILL DEVELOP OVER THE PENINSULA EACH LATE AFTERNOON PUSHING W INTO THE SW GULF EACH EVENING. CARIBBEAN SEA... THE MAIN IMPACT FOR THE CARIBBEAN BASIN THIS EVENING IS THREE TROPICAL WAVES WHICH ARE MOVING WESTWARD. WHILE THOSE ARE DETAILED ABOVE...WATER VAPOR IMAGERY INDICATES THAT MOST OF THE MOISTURE IS FOUND E OF 72W AS DRY AIR ALOFT REMAINS IN PLACE OVER THE WESTERN CARIBBEAN IN ASSOCIATION WITH AN UPPER LEVEL RIDGE ANCHORED NEAR 13N80W. FARTHER EAST...MOISTURE AND CLOUDINESS INCREASES WITH LOW-LEVEL MOISTURE CONVERGENCE OCCURRING ALONG A LINE EXTENDING FROM 12N61W TO 14N70W N OF THE A-B-C ISLANDS. WIDELY SCATTERED SHOWERS AND TSTMS ARE OCCURRING S OF THIS LINE AND ALSO NEAR THE EASTERN TWO TROPICAL WAVE AXIS AS IS DESCRIBED IN DETAILED ABOVE. MODERATE TO FRESH BREEZE TRADES ARE EXPECTED TO PERSIST THROUGH LATE THURSDAY EXCEPT IN THE S CENTRAL PORTION WHERE THE PRESSURE GRADIENT WILL BE THE MOST TIGHT BETWEEN CENTRAL ATLC HIGH PRESSURE N-NE OF THE AREA AND LOW PRESSURE OVER NORTHERN COLOMBIA...RESULTING IN FRESH TO STRONG TRADES. WINDS ARE ALSO FORECAST TO PULSE TO FRESH TO STRONG LEVELS IN THE GULF OF HONDURAS DURING THE OVERNIGHT HOURS DUE TO A LOCALLY AND DIURNALLY DRIVEN STRENGTHENING PRESSURE GRADIENT. ...HISPANIOLA... CURRENTLY...THE NORTHERN PORTION OF A TROPICAL WAVE IS HELPING TO IGNITE SCATTERED SHOWERS AND TSTMS ACROSS THE ISLAND E OF 70W WITH ISOLATED ACTIVITY ALSO NOTED TO THE W ACROSS NORTHERN HAITI. THE PASSAGE OF THE TROPICAL WAVE DURING THE NEXT 24 HOURS OR SO WILL RESULT IN A CONTINUED HIGHER PROBABILITY OF SCATTERED SHOWERS AND TSTMS...ESPECIALLY DURING THE AFTERNOON AND EVENING HOURS WITH THE ADDITION OF DAYTIME HEATING. ATLANTIC OCEAN... NORTH-NORTHEASTERLY FLOW ALOFT PREVAILS OVER MUCH OF THE SW NORTH ATLC BETWEEN AN UPPER LEVEL ANTICYCLONE CENTERED NEAR 30N79W AND AN UPPER LEVEL LOW CENTERED NEAR 23N63W. WHILE OVERALL CONDITIONS REMAIN STABLE ACROSS THE SW NORTH ATLC WITHIN A SURFACE RIDGE WITH AXIS ALONG 26N/27N...LOW-LEVEL MOISTURE CONVERGENCE IS MAXIMIZED ALONG A LINE FROM 26N80W TO 31N74W WITH ISOLATED SHOWERS AND TSTMS OCCURRING N OF THIS LINE. FARTHER EAST...WITHIN THE INFLUENCE OF THE UPPER LEVEL LOW...A SURFACE TROUGH...THE NORTHERN PIECE OF ENERGY FRACTURED AWAY FROM A TROPICAL WAVE IN THE CARIBBEAN SEA ALONG 68W...IS GENERATING SCATTERED SHOWERS AND ISOLATED TSTMS WITHIN 45 NM EITHER SIDE OF A LINE FROM 28N54W TO 20N67W. OTHERWISE...A NEARLY STATIONARY RIDGE ANCHORED BY A 1023 MB HIGH CENTERED NEAR 28N46W INFLUENCES THE REMAINDER OF THE CENTRAL AND EASTERN ATLC. FOR ADDITIONAL INFORMATION PLEASE VISIT HTTP://WWW.HURRICANES.GOV/MARINE $$ LEWITSKY