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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