[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 061802
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN SEP 06 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1745 UTC.

...SPECIAL FEATURES...

THE CENTER OF TROPICAL DEPRESSION FRED AT 06/15 UTC IS NEAR
25.7N 43.2W. FRED IS MOVING TOWARD THE NORTH...OR 5 DEGREES AT 8
KT. THE MINIMUM CENTRAL PRESSURE IS 1010 MB. MAXIMUM SUSTAINED
WIND SPEED IS 30 KT WITH GUSTS TO 40 KT. PUBLIC ADVISORIES ABOUT
FRED ARE BEING ISSUED UNDER THE WMO HEADER WTNT31 KNHC...AND
UNDER THE AWIPS HEADER MIATCPAT1. FORECAST/ADVISORIES BEING
ISSUED UNDER THE WMO HEADER WTNT21 KNHC...AND UNDER THE AWIPS
HEADER MIATCMAT1. CONVECTIVE PRECIPITATION...SCATTERED MODERATE
TO ISOLATED STRONG WITH TSTMS FROM 22N TO 29N BETWEEN 39W AND
45W.

THE CENTER OF TROPICAL STORM GRACE AT 06/1500 UTC IS NEAR 12.9N
29.9W. GRACE IS MOVING TOWARD THE WEST...OR 280 DEGREES AT 12
KT. THE MINIMUM CENTRAL PRESSURE IS 1004 MB. MAXIMUM SUSTAINED
WIND SPEED IS 40 KT WITH GUSTS TO 50 KT. PUBLIC ADVISORIES ABOUT
GRACE ARE BEING ISSUED UNDER THE WMO HEADER WTNT32 KNHC...AND
UNDER THE AWIPS HEADER MIATCPAT2. FORECAST/ADVISORIES ARE BEING
ISSUED UNDER THE WMO HEADER WTNT22 KNHC...AND UNDER THE AWIPS
HEADER MIATCMAT2. CONVECTIVE PRECIPITATION...SCATTERED MODERATE
FROM 08N TO 16N BETWEEN 26W AND 32W.

...TROPICAL WAVES...

A TROPICAL WAVE IS OVER THE CENTRAL ATLC...AHEAD OF TROPICAL
STORM GRACE...WITH AXIS NEAR 38W MOVING W AT APPROXIMATELY 15 KT
OVER THE PAST 24 HOURS. CIRA LAYER PRECIPITABLE WATER IMAGERY
SHOW THERE IS DRY AIR IN THE WAVE ENVIRONMENT...COINCIDING WITH
SAHARAN AIR DEPICTED IN METEOSAT ENHANCED IMAGERY. ISOLATED
SHOWERS ARE FROM 12N TO 13N BETWEEN 37W AND 39W.

A TROPICAL WAVE IS WITHIN 500 NM E OF THE LESSER ANTILLES. THIS IS
A LOW-AMPLITUDE WAVE WITH A WELL DEFINED INVERTED-V WIND PATTERN
AT 700 MB AND A WEAK CYCLONIC SWIRL NEAR THE SURFACE. CIRA LAYER
PRECIPITABLE WATER IMAGERY SHOW MODERATE MOISTURE ASSOCIATED
WITH THIS WAVE MAINLY WITHIN 320 NM AHEAD OF ITS AXIS S OF 14N
WHERE SCATTERED SHOWERS ARE OBSERVED.

A TROPICAL WAVE IS OVER THE E CARIBBEAN WITH AXIS NEAR
68W...MOVING W AT 15 TO 20 KT OVER THE PAST 24 HOURS. CIRA LAYER
PRECIPITABLE WATER IMAGERY FROM SURFACE TO 850 MB SHOW A
MODERATE AIRMASS AHEAD OF THE WAVE AXIS AND DRY AIR BEHIND IT.
THE MOISTURE AND A SLIGHT DIFFLUENT MIDDLE-LEVEL ENVIRONMENT MAY
ENHANCE SCATTERED SHOWERS AND TSTMS OVER PUERTO RICO AND
ADJACENT WATERS LATER TODAY.

A TROPICAL WAVE IS OVER THE CENTRAL CARIBBEAN WITH AXIS ALONG
74W...MOVING W AT 15 TO 20 KT OVER THE PAST 24 HOURS. THE WAVE
IS ASSOCIATED MAINLY WITH MODERATE MOISTURE FROM THE SURFACE TO
850 MB ACCORDING TO CIRA LAYER PRECIPITABLE WATER IMAGERY.
HOWEVER...STRONG DEEP LAYER WIND SHEAR AND DRY AIR
SUBSIDENCE FROM ALOFT HINDER CONVECTION DEVELOPMENT AT THE TIME.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH PASSES OVER COASTAL SECTIONS OF AFRICA NEAR
12N16W TO 10N21W. THE ITCZ BEGINS NEAR 09N41W AND CONTINUES TO
09N49W TO 09N56W. ASIDE THE CONVECTION ASSOCIATED WITH
GRACE...SCATTERED MODERATE CONVECTION IS OFF THE WESTERN COAST
OF AFRICA FROM 06N TO 15N E OF 20W...ASSOCIATED WITH BOTH THE
NEXT TROPICAL WAVE TO COME OFF THE COAST AND THE MONSOON TROUGH.

...DISCUSSION...

GULF OF MEXICO...

A BROAD SURFACE RIDGE COVERS THE EASTERN CONUS AND EXTENDS A
RIDGE AXIS ACROSS THE N-NE GULF OF MEXICO. IN THE GULF...A
WEAKNESS IN THIS RIDGE IS ANALYZED AS A 1017 MB LOW NEAR 27N85W.
ALOFT...A BROAD ANTICYCLONE IS CENTERED OVER TEXAS EXTENDING
INTO THE W-NW BASIN WHILE AN ELONGATED LOW WITH ASSOCIATED
TROUGH COVER MOST OF THE EASTERN CONUS WITH A BASE EXTENDING TO
THE BAY OF CAMPECHE AND THE YUCATAN PENINSULA. THIS WIND PATTERN
ALOFT IS GENERATING A DIFFLUENT ENVIRONMENT THAT ALONG WITH
SHALLOW MOISTURE BEING ADVECTED FROM THE CARIBBEAN SUPPORT
SCATTERED MODERATE CONVECTION AND TSTMS N OF 25N E OF 93W AND
ISOLATED SHOWERS AND TSTMS IN THE SE GULF. WINDS ACROSS THE GULF
CONTINUE TO BE VARIABLE AND LIGHT. WEAK RIDGING WILL
CONTINUE ACROSS THE BASIN THE NEXT TWO DAYS.

CARIBBEAN SEA...

TWO TROPICAL WAVES ARE OVER THE BASIN. NONE PRODUCING
SIGNIFICANT WEATHER AT THE TIME. SEE THE TROPICAL WAVES SECTION
FOR MORE DETAILS. THE EASTERN PORTION OF AN UPPER TROUGH
EXTENDING ALONG THE EASTERN CONUS WITH BASE REACHING THE S-SW
GULF OF MEXICO ALONG WITH AN UPPER RIDGE CENTERED OVER THE SW
CARIBBEAN CONTINUE TO GENERATE A DIFFLUENT ENVIRONMENT OVER THE
NW CARIBBEAN THAT ENHANCES ISOLATED SHOWERS AND TSTMS W OF 80W.
OVER THE SW BASIN...THE MONSOON TROUGH CONTINUE TO SUPPORT
SCATTERED MODERATE CONVECTION AND ISOLATED TSTMS S OF 13N W OF
75W. EXCEPT FOR SCATTERED TO ISOLATED SHOWERS OVER THE WINDWARD
ISLANDS...THE REMAINDER BASIN IS DEVOID OF CONVECTION BEING
INFLUENCED BY DRY AIR SUBSIDENCE AND STRONG DEEP LAYER WIND
SHEAR. THE WAVES ARE EXPECTED TO BE OVER THE W BASIN BY TUESDAY
MORNING.

...HISPANIOLA...

SHALLOW MOISTURE AND A MIDDLE TO UPPER LEVEL DIFFLUENT
ENVIRONMENT ALOFT SUPPORT ISOLATED SHOWERS AND TSTMS OVER THE NE
DOMINICAN REPUBLIC. THE PASSAGE OF TWO TROPICAL WAVES OVER
THE ISLAND IS EXPECTED TO GENERATE SOME SHOWERS THROUGH MONDAY.

ATLANTIC OCEAN...

THE MAIN FEATURES IN THE BASIN CONTINUE TO BE TROPICAL
DEPRESSION FRED AND TROPICAL STORM GRACE...BOTH DISCUSSED IN THE
SPECIAL FEATURES SECTION. TWO TROPICAL WAVES ARE AHEAD OF
GRACE...NONE GENERATING SIGNIFICANT WEATHER AT THE TIME. PLEASE
REFER TO THE TROPICAL WAVES SECTION FOR MORE DETAILS. WEAK LOW
PRESSURE DOMINATES THE SW N ATLC WATERS BEING SUPPORTED BY A LOW
ALOFT CENTERED OVER THE SE CONUS. ONE SURFACE TROUGH IS ANALYZED
IN THIS REGION FROM 28N70W SW TO 25N75W AND ENHANCES ISOLATED
SHOWERS AND TSTMS OVER THE NORTHERN BAHAMAS AND FROM 25N TO 28N
BETWEEN 65W AND 72W. A MIDDLE TO UPPER LEVEL TROUGH IS OVER THE
CENTRAL ATLC WITH BASE REACHING NEARLY 30N...SUPPORTING A
FRONTAL SYSTEM ANALYZED AS A STATIONARY FRONT FROM 30N52W TO
30N60W TO 29N67W. SCATTERED MODERATE CONVECTION IS N OF 27N
BETWEEN 45W AND 51W. WEAK RIDGING DOMINATES ELSEWHERE.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

$$
NR
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