[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 182348
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI SEP 18 2009

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...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURES...

AN AREA OF SHOWERS AND TSTMS ASSOCIATED WITH A 1008 MB LOW NEAR
13N40W CONTINUES TO BECOME BETTER ORGANIZED. SCATTERED MODERATE/
ISOLATED STRONG CONVECTION IS MAINLY TO THE E OF THE LOW CENTER
FROM 12N-17N BETWEEN 35W-42W. UPPER LEVEL WIND CONDITIONS REMAIN
ONLY MODERATELY FAVORABLE FOR FURTHER DEVELOPMENT. THERE IS A
MEDIUM CHANCE...30 TO 50 PERCENT...OF THIS SYSTEM BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HRS.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 25W S OF 18N MOVING W NEAR 15 KT. THE
WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN
TOTAL PRECIPITABLE WATER IMAGERY AS WELL AS A MAXIMUM IN 85O MB
VORTICITY NEAR THE WAVE AXIS FROM 10N-16N BETWEEN 20W-27W AS
DEPICTED BY THE CIMSS WAVETRAK MODEL GUIDANCE. SCATTERED
MODERATE CONVECTION IS FROM 14N-19N BETWEEN 19W-28W.

TROPICAL WAVE IS ALONG 90W S OF 21N MOVING W NEAR 15 KT. THE
WAVE LIES WITHIN A BROAD AREA OF DEEP LAYER MOISTURE ACROSS A
LARGE PORTION OF CENTRAL AMERICA AND SRN MEXICO. THIS DEEP LAYER
MOISTURE...ATMOSPHERIC INSTABILITY AND FORCING DUE TO THE WAVE
IS GENERATING SCATTERED MODERATE TO STRONG CONVECTION OVER THE
YUCATAN PENINSULA AND PORTIONS OF GUATEMALA FROM 16N-22N BETWEEN
87W-91W.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 15N17W 15N24W 13N27W 14N36W
10N41W 9N62W. TOTAL PRECIPITABLE WATER IMAGERY INDICATES A LARGE
AREA OF MAXIMUM VALUES ACROSS THE ERN TROPICAL ATLC FROM 9N-20N
BETWEEN THE W AFRICA COAST AND 40W. THIS AREA...INCLUDES THE
ITCZ AXIS AND SCATTERED SHOWERS AND POSSIBLE ISOLATED MODERATE
CONVECTION ARE N OF 10N TO 20N E OF 40W. ELSEWHERE...SCATTERED
MODERATE CONVECTION IS WITHIN 90 NM EITHER SIDE OF THE AXIS
BETWEEN 56W-62W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 2100 UTC...A SURFACE TROUGH EXTENDS INTO THE GULF OF
MEXICO FROM ERN LOUISIANA NEAR 29N90W ALONG 27N92W 26N97W.
LOW-LEVEL CONVERGENCE NEAR THE TROUGH IS SUPPORTING ISOLATED
SHOWERS WITHIN 60 NM EITHER SIDE OF THE BOUNDARY. A WARM FRONT
LIES INLAND OVER THE SE CONUS ALONG 31N EXTENDING FROM A 1012 MB
LOW CENTERED OVER SWRN MISSISSIPPI AND IS PROVIDING THE ERN GULF
WITH MAINLY WEAK SOUTHERLY SURFACE FLOW OF 5-10 KT. ISOLATED
SHOWERS ARE OVER THE ERN GULF N OF 23N E OF 90W. THIS LOW
PRESSURE SYSTEM AND SURFACE BOUNDARIES ARE SUPPORTED ALOFT BY AN
UPPER LEVEL TROUGH WITH AXIS ALONG 90W ACROSS MUCH OF THE
CENTRAL GULF. AN UPPER LEVEL RIDGE CENTERED OVER E/CENTRAL
MEXICO NEAR 20N99W COVERS THE SW GULF AND BAY OF CAMPECHE. UPPER
LEVEL DIFFLUENCE IS ENHANCING AN AREA OF SCATTERED SHOWERS AND
ISOLATED TSTMS S OF 26N W OF 95W. ANOTHER UPPER LEVEL RIDGE IS
CENTERED OVER THE NW BAHAMAS NEAR 26N78W AND EXTENDS ACROSS THE
FAR SE GULF. UPPER LEVEL DIFFLUENCE BETWEEN THIS RIDGE AND THE
UPPER LEVEL TROUGH IS ENHANCING SCATTERED SHOWERS AND TSTMS
ACROSS THE FAR SWRN FLORIDA PENINSULA AND ADJACENT COASTAL
WATERS N OF THE FLORIDA KEYS.

CARIBBEAN SEA...
SCATTERED SHOWERS AND TSTMS ARE OCCURRING ACROSS THE YUCATAN
PENINSULA FROM 16N-22N BETWEEN 87W-91W DUE TO THE TROPICAL WAVE
ALONG 90W. THIS ACTIVITY IS BEING ENHANCED BY UPPER LEVEL
DIFFLUENCE AS THE CONVECTION MOVES WWD AND UNDER THE INFLUENCE
OF AN UPPER LEVEL HIGH CENTERED OVER E/CENTRAL MEXICO. UPPER
LEVEL RIDGING EXTENDS ACROSS THE YUCATAN PENINSULA OVER CUBA AND
INTO THE W ATLC PROVIDING AN UPPER LEVEL DIFFLUENT ENVIRONMENT
FOR SCATTERED SHOWERS AND TSTMS ACROSS CUBA AND PORTIONS OF THE
NW CARIBBEAN N OF 18N. AN UPPER LEVEL LOW IS CENTERED FARTHER TO
THE SE OVER THE SW CARIBBEAN NEAR 13N80W. THIS UPPER LEVEL LOW
IS SUPPORTING AREAS OF SCATTERED SHOWERS AND TSTMS ACROSS
PORTIONS OF SW HISPANIOLA EXTENDING TO JAMAICA AND OVER PORTIONS
OF HONDURAS AND NICARAGUA. ON THE ERN PERIPHERY OF THE UPPER
LEVEL LOW ACROSS THE CENTRAL CARIBBEAN MOIST SOUTHERLY DIFFLUENT
FLOW IS NOTED ON WATER VAPOR IMAGERY AND IS GENERATING ISOLATED
SHOWERS AND POSSIBLE ISOLATED TSTMS ACROSS THE ERN CARIBBEAN E
OF 72W. MODERATE TRADE WINDS CONTINUE ACROSS MUCH OF THE BASIN
AS A RELATIVELY WEAK PRESSURE GRADIENT REMAINS IN PLACE.

ATLANTIC OCEAN...
A SURFACE TROUGH EXTENDS FROM NEAR 31N72W ACROSS THE NW BAHAMAS
TO NEAR 23N80W. LOW-LEVEL CONVERGENCE NEAR THE TROUGH IS
SUPPORTING ISOLATED SHOWERS AND POSSIBLE TSTMS WITHIN 60 NM
EITHER SIDE OF THE SURFACE TROUGH. TO THE NORTH...A STATIONARY
FRONT EXTENDS FROM N OF THE DISCUSSION AREA TO 32N72W WWD TO THE
GEORGIA COAST. MOST SHOWER ACTIVITY ASSOCIATED WITH THE FRONT
HOWEVER IS LOCATED N OF 32N BETWEEN 70W-82W. FARTHER SE...A
SURFACE TROUGH IS ANALYZED FROM 28N66W THROUGH A 1013 MB
LOW...THE REMNANTS OF FRED...TO 23N68W. SCATTERED SHOWERS AND
ISOLATED TSTMS ARE WITHIN 120 NM EITHER SIDE OF THE TROUGH AXIS.
MOST OF THIS ACTIVITY ACROSS THE W ATLC IS SUPPORTED ALOFT BY
UPPER DIFFLUENCE ASSOCIATED WITH AN UPPER LEVEL ANTICYCLONIC
CIRCULATION CENTERED OVER THE NW BAHAMAS NEAR 26N78W. THE
REMAINDER OF THE CENTRAL AND ERN ATLC IS DOMINATED BY A BROAD
SURFACE RIDGE ANCHORED BY A 1024 MB HIGH NEAR 33N43W AND A 1023
MB HIGH NEAR 34N19W. IN THE UPPER LEVELS...AN UPPER LEVEL LOW IS
CENTERED NEAR 21N63W. LIFT AND INSTABILITY IN THE VICINITY OF
THE LOW IS GENERATING SCATTERED SHOWERS AND ISOLATED TSTMS FROM
18N-22N BETWEEN 60W-66W. AN UPPER LEVEL TROUGH EXTENDS ACROSS
THE NE ATLC WITH AXIS ALONG 30N21W TO 22N37W.

$$
HUFFMAN



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