[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 131622
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN SEP 13 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
1600 UTC.

...SPECIAL FEATURE...

A BROAD AND ELONGATED CIRCULATION IS FORMING ALONG THE MONSOON
TROUGH NEAR 10N33W AT THE A THE BASE OF A TROPICAL WAVE THAT
EXTENDS NORTH TO 17N33W. THE TROPICAL WAVE IS FAIRLY LOW
AMPLITUDE AT THIS TIME...AND IS LIKELY A WEAK AND DRY NORTHERN
VORTICY THAT MOVED OFF THE AFRICAN COAST OVER THE LAST COUPLE OF
DAYS AND HAS COME INTO PHASE WITH THE DEVELOPING CIRCULATION.
MOST OF THE CONVECTION IS RELEGATED TO THE SOUTH WITH THE THIS
ELONGATED CIRCULATION...FROM 09N TO 12N BETWEEN 30W AND 35W. THE
BROAD CIRCULATION IS EXPECTED TO FORM INTO A DISTINCT AND
COHERENT LOW PRES SYSTEM LATER TODAY...AND HAS A MEDIUM CHANCE
OF DEVELOPMENT INTO A TROPICAL CYCLONE OVER THE NEXT 48 HOURS.

...TROPICAL WAVES...

TROPICAL WAVE EXTENDS FROM 11N54W TO 18N53W MOVING W AT 15-20
KT. THE WAVE COINCIDES WITH A BROAD 700 MB TROUGHING BETWEEN 49W-
57W. NO SIGNIFICANT CONVECTION IS OCCURRING WITH THE WAVE AT
THIS TIME.

TROPICAL WAVE EXTENDS FROM 11N73W TO 20N72W MOVING W AT 15 KT.
THE WAVE COINCIDES WITH A 700 MB TROUGHING BETWEEN 70W-75W AND A
850 MB RELATIVE VORTICITY MAXIMUM NEAR 20N72W. ISOLATED MODERATE
CONVECTION IS FROM 16N-22N BETWEEN 65W-72W.

TROPICAL WAVE EXTENDS FROM NE COLOMBIA TO WESTERN HAITI MOVING W
AT 15-20 KT. THE WAVE HAS MIGRATED TO THE DRIER AND SUBSIDENT
WEST SIDE OF AN UPPER CYCLONE CENTERED OVER HISPANIOLA...AND NO
SIGNFICANT CONVECTION IS NOTED.

...ITCZ/MONSOON TROUGH...
THE MONSOON TROUGH EXTENDS FROM THE SENEGAL COAST NEAR 15N17W TO
14N25W TO 09N33W TO 11N50W. SCATTERED MODERATE CONVECTION IS
NOTED WITHIN 30 NM OF THE AXIS BETWEEN 20W AND 30W. SCATTERED
MODERATE TO ISOLATED STRONG CONVECTION IS NOTED WITHIN 180 NM N
OF THE AXIS BETWEEN 30W AND 45W.

...DISCUSSION...

GULF OF MEXICO... A COLD FRONT REACHES FROM THE NORTHERN FLORIDA
PENINSULA NEAR 29N82W TO 26N93W. THE FRONT MARKS A WELL DEFINED
CONTRAST WITH DRIER AND SLIGHTLY COOLER AIR NOTED IN THE SURFACE
OBSERVATIONS ACROSS THE DEEP SOUTH SOUTH STATES AND INTO THE
NORTHERN GULF. A LARGE MASS OF MODERATE TO STRONG CONVECTION HAS
BEEN ONGOING OVER MUCH OF THE SW AND WEST CENTRAL GULF OF
MEXICO...ALTHOUGH THE AREA APPEARS TO BE DIMINISHING AND IS
MOSTLY CENTERED WITHIN 60 NM OF 23N95W. THE CONVECTION IS BEING
ENHANCED BY UPPER LEVEL DIVERAGNE IN DEFORMATION AREA BETWEEN A
BROAD LONG WAVE TROUGH MOVING INTO THE EASTERN UNITED STATES AND
AN UPPER ANTICYCLONE CENTERED OVER W CENTRAL MEXICO. LOOKING
AHEAD...THE FRONT WILL STALL ACROSS THE CENTRAL GULF OVER THE
NEXT 24 TO 48 HOURS BEFORE LIFTING NORTH AND BECOMING DIFFUSE AS
SHOWERS AND THUNDERSTORMS WILL PULSE ALONG THE DYING FRONTAL
BOUNDARY.

CARIBBEAN SEA...GENERALLY NORTHERLY FLOW ALOFT PREVAILS OVER
MUCH OF THE WESTERN CARIBBEAN THIS MORNING BETWEEN AN UPPER
LEVEL RIDGE ANCHORED OVER WEST-CENTRAL MEXICO AND AN UPPER LEVEL
LOW CENTERED OVER HISPANIOLA WITH AN UPPER TROUGH REACHING
TOWARD THE GULF OF HONDURAS. DIVERENCE ALOFT ASSOCIATED WITH THE
UPPER TROUGH WAS INTERACTING WITH TRADE WIND CONVERGENCE AND
MORNING OFFSHORE FLOW TO PRODUCE CLUSTERS OF SHOWERS AND
THUNDERSTORMS OFF THE COAST OF NICARAGUA...ALTHOUGH THIS IS NOW
DIMINISHING AS THE OFFSHORE FLOW SHUTS OFF. GENERALLY FAIR
WEATHE PERSISTS ELSEWHERE ACROSS THE CARIBBEAN.

HISPANIOLA...A TROUGH EXTENDS ACROSS THE EASTERN DOMINICAN
REPUBLIC NORTHWARD TO 22N67W. THE TROUGH SPLIT FROM THE NORTHERN
PORTION OF A TROPICAL WAVE NOW LOCATED BETWEEN NE COLOMBIA AND
WESERN HAITI. A FEW SHOWERS AND THUNDSTORMS ARE NOTED OFF BOTH
THE NORTH AND SOUTH COASTS OF THE DOMINCAN REPUBLIC...ENHANCED
BY AN UPPER LOW CENTERED OVER THE CENTRAL PORTIONS OF THE
ISLAND. THIS WILL ALSO ENHANCE AFTERNOON CONVECTION RELATED TO
SEA BREEZE CONVERGENCE OVER MUCH OF EASTERN AND CENTRAL
DOMINICAN REPUBLIC THROUGH THE REMAINDER OF THE DAY.

ATLANTIC OCEAN...
MIDDLE TO UPPER LEVEL ENERGY ASSOCIATED WITH LONGWAVE TROUGHING
OVER THE EASTERN CONUS IS SUPPORTING A COLD FRONT FROM 31N79W TO
30N81W...AND A PRE-FRONTAL TROUGH FROM 30N80W ACROSS FLORIDA TO
TAMPA BAY. A LARGE AREA OF MODERATE TO STRONG SHOWERS AND
THUNDTORMS IS NOTED WITHIN 180 NM AHEAD OF THE FRONT AND NORTH
OF THE BAHAMAS. THE SUBTROPICAL RIDGE PERSISTS FROM THE N
CENTRAL ATLC TO THE NORTHERN BAHAMAS. A WEAK 1018 MB LOW IS
EMBEDDED WITHIN THE SOUTHERN PERIPHERY OF THE RIDGE CENTERED
NEAR 30N42W THAT CONTINUES TO GENERATE AN AREA OF SCATTERED
SHOWERS AND ISOLATED TSTMS FROM 25N-33N BETWEEN 42W-49W.

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

$$
CHRISTENSEN
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