891  
AXNT20 KNHC 172350  
TWDAT  
 
TROPICAL WEATHER DISCUSSION  
NWS NATIONAL HURRICANE CENTER MIAMI FL  
750 PM EDT THU AUG 17 2017  
 
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
 
 
AT 17/2100 UTC, GERT BECOMES A POST-TROPICAL CYCLONE AND THE LAST  
ADVISORY WAS ISSUED BY THE NATIONAL HURRICANE CENTER ON THIS  
SYSTEM. AT THIS TIME, THE CENTER OF POST-TROPICAL CYCLONE GERT IS  
CENTERED NEAR 44.8N 46.0W OR ABOUT 745 NM E OF HALIFAX NOVA SCOTIA  
MOVING TOWARD THE ENE OR 60 DEGREES AT 34 KT. ESTIMATED MINIMUM  
CENTRAL PRESSURE IS 985 MB. MAXIMUM SUSTAINED WIND SPEED IS 55 KT  
WITH GUSTS TO 65 KT. SEE LATEST NHC FORECAST/ADVISORY UNDER  
AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS.  
 
AT 17/2100 UTC, POTENTIAL TROPICAL CYCLONE NINE IS UPGRADED TO  
TROPICAL STORM HARVEY BASED ON REPORTS FROM AN AIR FORCE RESERVE  
HURRICANE HUNTER AIRCRAFT. AT THIS TIME, THE CENTER OF TROPICAL  
STORM HARVEY IS LOCATED NEAR 13.0N 55.8W OR ABOUT 220 NM E OF  
BARBADOS MOVING W AT 16 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS  
1004 MB. MAXIMUM SUSTAINED WIND SPEED HAS INCREASED TO 35 KT WITH  
GUSTS TO 45 KT. A CLUSTER OF STRONG CONVECTION IS NOTED WITHIN  
ABOUT 120 NM WEST SEMICIRCLE OF CENTER. SCATTERED MODERATE TO  
ISOLATED STRONG CONVECTION IS ELSEWHERE FROM 12N-15N BETWEEN 55W-  
59W. HARVEY SHOULD MOVE THROUGH THE WINDWARD ISLANDS AND INTO THE  
EASTERN CARIBBEAN SEA ON FRIDAY. SLOW STRENGTHENING IS POSSIBLE  
DURING THE NEXT 48 HOURS. HARVEY IS EXPECTED TO PRODUCE RAINFALL  
TOTALS OF 2 TO 4 INCHES ACROSS PORTIONS OF THE WINDWARD ISLANDS  
FROM MARTINIQUE SOUTHWARD TO GRENADA. THESE RAINS COULD CAUSE  
LIFE-THREATENING FLASH FLOODS AND MUDSLIDES. SEE SEE THE LATEST  
NHC INTERMEDIATE PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS  
MIATCPAT4/WTNT34 KNHC, AND THE FULL FORECAST/ADVISORY UNDER  
AWIPS/WMO HEADERS MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS.  
 
A TROPICAL WAVE EXTENDS FROM 20N44W TO 10N45W. A 1009 MB LOW  
PRESSURE IS ALONG THE WAVE AXIS NEAR 15.3N 44.8W. SCATTERED  
MODERATE CONVECTION IS NOTED MAINLY ON THE WEST SEMICIRCLE OF THE  
LOW CENTER FROM 14N-18N BETWEEN THE WAVE AXIS AND 47W. THE SHOWER  
AND THUNDERSTORM ACTIVITY ASSOCIATED WITH THIS AREA OF LOW  
PRESSURE HAS CHANGED LITTLE IN ORGANIZATION DURING THE PAST  
SEVERAL HOURS. HOWEVER, ONLY A SLIGHT INCREASE IN THE ORGANIZATION  
OF THE SHOWER ACTIVITY COULD LEAD TO THE FORMATION OF A TROPICAL  
DEPRESSION DURING THE NEXT COUPLE OF DAYS BEFORE UPPER-LEVEL WINDS  
BECOME LESS FAVORABLE FOR DEVELOPMENT EARLY NEXT WEEK. THE LOW IS  
EXPECTED TO MOVE WEST-NORTHWESTWARD AT ABOUT 15-20 KT DURING THE  
NEXT FEW DAYS, AND INTERESTS IN THE NORTHERN LEEWARD ISLANDS  
SHOULD MONITOR THE PROGRESS OF THIS DISTURBANCE. THIS SYSTEM HAS  
NOW A HIGH CHANGE OF BECOMING A TROPICAL CYCLONE THROUGH 48 HOURS.  
   
..TROPICAL WAVES
 
 
A TROPICAL WAVE IS MOVING ACROSS THE CABO VERDE ISLANDS AND  
EXTENDS FROM 18N24W TO 06N25W. A 1010 MB LOW PRESSURE IS ALONG THE  
WAVE AXIS NEAR 10N25W. SCATTERED MODERATE CONVECTION IS FROM  
08N-12N BETWEEN THE WAVE AXIS AND 22W, AND AHEAD OF THE LOW CENTER  
FROM 06N-10N BETWEEN 25W-30W. THIS WAVE IN A VERY MOIST AREA  
BASED ON TPW IMAGERY AND HAS A WELL PRONOUNCED 700 MB TROUGH.  
GRADUAL DEVELOPMENT OF THIS SYSTEM IS POSSIBLE THROUGH THE MIDDLE  
OF NEXT WEEK WHILE THE WAVE MOVES WESTWARD TO WEST-NORTHWESTWARD AT  
ABOUT 15-20 KT. CURRENTLY, THIS SYSTEM HAS A LOW CHANGE OF BECOMING  
A TROPICAL CYCLONE THROUGH 5 DAYS.  
 
A STRONG AND BROAD TROPICAL WAVE IS MOVING WESTWARD ACROSS THE  
CARIBBEAN SEA, AND EXTENDS ALONG 70W/71W. A CLUSTER OF NUMEROUS  
MODERATE ISOLATED STRONG CONVECTION IS NOTED OVER THE NORTHER PART  
OF THE WAVE AXIS AND COVERS FROM 18N-21.5N BETWEEN 68W-71W. THIS  
CONVECTIVE ACTIVITY IS AFFECTING THE EASTERN PART OF DOMINICAN  
REPUBLIC. SCATTERED MODERATE ISOLATED STRONG CONVECTION IS NOTED  
ELSEWHERE FROM 20N-24N BETWEEN 66W-72W. THE WAVE SHOWS UP VERY  
WELL ON THE TPW ANIMATION AND 700 MB STREAMLINE ANALYSIS. MOISTURE  
ASSOCIATED WITH THIS WAVE WILL SPREAD ACROSS THE TURKS AND CAICOS  
ISLANDS, THE SE BAHAMAS, AND THE REMAINDER OF HISPANIOLA TONIGHT  
INCREASING THE LIKELIHOOD OF RAIN. THE WAVE IS FORECAST TO MOVE  
ACROSS THE SE BAHAMAS, EASTERN CUBA AND JAMAICA ON FRIDAY. FRESH  
TO LOCALLY STRONG NE WINDS ARE NOTED OVER WATERS AHEAD OF THE  
WAVE AXIS.  
 
A TROPICAL WAVE IS OVER THE YUCATAN PENINSULA AND GUATEMALA, WITH  
AXIS ALONG 90W/91W. THE WAVE IS HELPING TO INDUCE SCATTERED SHOWERS  
AND THUNDERSTORMS OVER PARTS OF THE YUCATAN PENINSULA, SE MEXICO  
AND GUATEMALA. THE WAVE COINCIDES WITH A 700 MB TROUGH, AND IS WELL  
DEPICTED IN THE MOISTURE PRODUCT.  
   
..ITCZ/MONSOON TROUGH
 
 
THE MONSOON TROUGH EXTENDS FROM THE AFRICAN COAST NEAR 13N16W TO  
A 1010 MB LOW PRESSURE 10N25W TO 09N30W TO 10N37W. TO THE WEST,  
THE MONSOON TROUGH AND ITCZ IS DISRUPTED DUE TO THE TROPICAL  
SYSTEMS AND TROPICAL WAVES MENTIONED ABOVE. OTHERWISE, SCATTERED  
MODERATE CONVECTION IS FROM 05N-08N BETWEEN 30W-41W.  
   
..DISCUSSION
 
 
GULF OF MEXICO...  
 
A 1020 MB HIGH CENTERED OVER NORTH-CENTRAL GULF OF MEXICO NEAR  
27N88W EXTENDS A RIDGE ACROSS THE REGION PRODUCING MAINLY GENTLE  
TO MODERATE WINDS BASED ON SCATTEROMETER DATA. A THERMAL TROUGH  
WILL DEVELOP DURING THE EVENING HOURS OVER THE YUCATAN PENINSULA  
BEFORE PUSHING OFFSHORE INTO THE SW GULF EACH NIGHT. A SURGE OF  
FRESH WINDS WILL ACCOMPANY THIS TROUGH. THE TROPICAL WAVE CURRENTLY  
MOVING ACROSS THE YUCATAN PENINSULA WILL ENHANCE THE PRESENCE OF  
THIS THERMAL TROUGH TONIGHT. LITTLE CHANGE IN THIS WEATHER PATTERN  
IS EXPECTED THROUGH EARLY NEXT WEEK. IN THE UPPER LEVELS, AN  
UPPER-LEVEL LOW CENTERED JUST NORTH OF TAMPICO, MEXICO IS HELPING  
TO INDUCE SOME SHOWER ACTIVITY OVER WESTERN GULF, MAINLY FROM  
20N-23N W OF 96W. ISOLATED SHOWERS AND TSTMS ARE NOTED OVER THE  
REMAINDER OF THE GULF WATERS, BUT PARTICULARLY FROM 23N-26N E OF  
90W.  
 
CARIBBEAN SEA...  
 
A TROPICAL WAVE IS ALONG 70W/71W, AND ANOTHER TROPICAL WAVE IS  
OVER THE YUCATAN PENINSULA. PLEASE, SEE THE TROPICAL WAVES SECTION  
FOR DETAILS. TROPICAL STORM HARVEY SHOULD MOVE THROUGH THE WINDWARD  
ISLANDS AND INTO THE EASTERN CARIBBEAN SEA ON FRIDAY. PLEASE, SEE  
SPECIAL FEATURES SECTION FOR MORE DETAILS. UPPER DIFFLUENT BETWEEN  
AN ANTICYCLONIC CIRCULATION CENTERED OVER THE SE CONUS AND AN  
UPPER-LEVEL LOW SPINNING OVER EASTERN CUBA SUPPORTS SCATTERED  
SHOWERS AND TSTMS OVER PARTS OF CENTRAL AND WESTERN CUBA. AS  
PREVIOUSLY MENTIONED, A TROPICAL WAVE NOW OVER HISPANIOLA WILL  
BRING MORE SHOWERS AND TSTMS OVER EASTERN CUBA ON FRIDAY, AND  
OVER WESTERN CUBA ON SATURDAY. SCATTERED SHOWERS AND TSTMS ARE  
ALSO NOTED OVER THE SW CARIBBEAN, LIKELY ASSOCIATED WITH THE  
EASTERN EXTENT OF THE PACIFIC MONSOON TROUGH COMBINED WITH A  
DIFFLUENT PATTERN ALOFT.  
   
..HISPANIOLA
 
 
A STRONG AND BROAD TROPICAL WAVE MOVING ACROSS HISPANIOLA WILL  
BRING SHOWERS AND TSTMS, AND GUSTY WINDS, WITH THE POTENTIAL OF  
LOCALLY HEAVY RAIN TONIGHT AND FRIDAY.  
 
ATLANTIC OCEAN...  
 
A PAIR OF TROPICAL WAVES AND TROPICAL STORM HARVEY ARE MOVING  
WESTWARD ACROSS THE TROPICAL ATLANTIC. THE NORTHERN PORTION OF  
A STRONG TROPICAL WAVE IS AFFECTING THE WATERS N OF HISPANIOLA.  
PLEASE, SEE SPECIAL FEATURES AND TROPICAL WAVE SECTIONS ABOVE FOR  
DETAILS. THE REMAINDER OF THE ATLANTIC IS UNDER THE INFLUENCE OF  
A RIDGE, WITH A CENTER OF 1024 MB LOCATED NEAR 32N41W. A BELT OF  
FRESH TO LOCALLY STRONG NE-E WINDS IS NOTED PER SCATTEROMETER  
DATA ROUGHLY BETWEEN 15N-22N DUE TO THE PRESSURE GRADIENT BETWEEN  
THE RIDGE AND THE TROPICAL SYSTEMS LOCATED BETWEEN THE COAST OF  
AFRICA AND THE LESSER ANTILLES.  
 
FOR ADDITIONAL INFORMATION PLEASE VISIT  
HTTP://WWW.HURRICANES.GOV/MARINE  
 

 
GR  
 
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