[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 312344
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT MON AUG 31 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
2300 UTC.

...SPECIAL FEATURES...

A BROAD AREA OF LOW PRESSURE ASSOCIATED WITH A 1008 MB LOW IS
CENTERED NEAR 15N54W...ABOUT 500 MILES E OF THE LESSER ANTILLES.
THE AREA COINCIDES WITH BROAD DEEP LAYER MOISTURE OBSERVED IN
TOTAL PRECIPITABLE WATER IMAGERY. MAXIMUM VALUES OF LOW-LEVEL
VORTICITY ARE ALSO OBSERVED IN THE VICINITY OF THE LOW BASED ON
CIMSS WAVETRAK MODEL GUIDANCE. A LARGE CLUSTER OF NUMEROUS
STRONG CONVECTION IS FROM 14N-18N BETWEEN 50W-53W. SCATTERED
MODERATE/STRONG CONVECTION IS FROM 11N-14N BETWEEN
51W-54W...FROM 18N-20N BETWEEN 48W-53W...AND FROM 13N-15N
BETWEEN 58W-59W. THIS SYSTEM HAS A HIGH CHANCE...GREATER THAN 50
PERCENT...OF BECOMING A TROPICAL DEPRESSION DURING THE NEXT DAY
OR SO AS IT MOVES WNW NEAR 15 KT. INTERESTS IN THE LESSER
ANTILLES SHOULD MONITOR THE PROGRESS OF THIS SYSTEM.

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 30W S OF 18N MOVING W NEAR 15 KT. THE
WAVE REMAINS EMBEDDED WITHIN A BROAD AREA OF MID-LEVEL CYCLONIC
CURVATURE IN THE VICINITY OF THE WAVE AXIS AS SEEN IN SATELLITE
IMAGERY AND SATELLITE DERIVED WINDS. THE WAVE COINCIDES WITH  A
RELATIVE MAXIMUM IN MOISTURE OBSERVED IN TOTAL PRECIPITABLE
WATER IMAGERY. HOWEVER...THE WAVE IS BEGINNING TO MOVE BENEATH A
VERY DRY AND SUBSIDENT AIR MASS ASSOCIATED WITH THE ERN EXTENT
OF AN UPPER LEVEL ANTICYCLONIC CIRCULATION CENTERED NEAR 17N47W
WHICH IS INHIBITING ANY DEEP CONVECTION.

A TROPICAL WAVE IS ALONG 79W S OF 18N MOVING W NEAR 15 KT. THE
WAVE IS EMBEDDED IN LOW-LEVEL TRADE WIND FLOW WITH SUBSIDENT DRY
AIR ALOFT MAKING IT DIFFICULT TO DISCERN THE LOCATION OF THE
WAVE AXIS. HENCE...POSITION IS BASED MAINLY ON CONTINUITY. THE
WAVE CONTINUES TO TRAIL AN AREA OF DEEP LAYER MOISTURE OBSERVED
IN TOTAL PRECIPITABLE WATER IMAGERY. NO DEEP CONVECTION IS
CURRENTLY ASSOCIATED WITH THE WAVE DUE TO THE DRY AIR ALOFT.
HOWEVER...A FEW SHOWERS/THUNDERSTORMS HAVE RECENTLY POPPED UP
OVER JAMAICA ALONG THE WAVE AXIS NEAR 18N. THIS ACTIVITY IS MOST
LIKELY DUE TO ATMOSPHERIC INSTABILITY REMAINING FROM DAYTIME
HEATING AND UPPER LEVEL DIFFLUENCE ALOFT.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 13N15W 11N27W 9N37W 13N47W
10N67W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM
11N-14N BETWEEN 13W-19W. SIMILAR ACTIVITY IS FROM 8N-10N BETWEEN
19W-22W...AND FROM 10N-11N BETWEEN 63W-66W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 2100 UTC...A STATIONARY FRONT EXTENDS ACROSS THE NRN GULF
FROM THE FLORIDA PANHANDLE NEAR 31N85W CONTINUING ALONG 29N91W TO
28N97W NEAR CORPUS CRISTI TEXAS. A PRE-FRONTAL SURFACE TROUGH IS
AHEAD OF THE FRONT EXTENDING FROM 29N83W TO 26N92W. SURFACE
CONVERGENCE NEAR THESE FEATURES IS SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS NW OF A LINE FROM 29N81W 25N89W 22N98W.
THE FRONT IS SUPPORTED BY AN UPPER LEVEL TROUGH OVER THE ERN
CONUS THAT EXTENDS INTO THE NRN GULF TO NEAR 28N89W. THE SHOWER
ACTIVITY IS ALSO ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN THE
UPPER LEVEL TROUGH AND AN UPPER LEVEL RIDGE THAT COVERS THE SW
GULF CENTERED OVER MEXICO NEAR 22N100W. A SECOND SURFACE TROUGH
EXTENDS ACROSS S FLORIDA FROM 27N80W NEAR HOBE SOUND TO NEAR
NAPLES FLORIDA CONTINUING TO 25N82W. SURFACE CONVERGENCE NEAR
THIS TROUGH IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS
S FLORIDA AND WRN CUBA S OF 27N E OF 85W. THIS ACTIVITY IS ALSO
ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN A SHORTWAVE UPPER
LEVEL RIDGE EXTENDING ACROSS S FLORIDA ALONG 27N82W TO 24N89W
AND AN UPPER LEVEL TROUGH E OF THE BAHAMAS.

CARIBBEAN SEA...
A SHORTWAVE INVERTED UPPER LEVEL TROUGH IS OVER THE YUCATAN
PENINSULA BETWEEN THE UPPER LEVEL RIDGE OVER THE SW GULF AND AN
UPPER LEVEL HIGH OVER THE W CARIBBEAN NEAR 18N81W. UPPER LEVEL
DIFFLUENCE BETWEEN THESE FEATURES IS SUPPORTING ISOLATED
SHOWERS/THUNDERSTORMS ACROSS THE NW CARIBBEAN FROM 15N-23N
BETWEEN 82W-91W. AN UPPER LEVEL TROUGH CENTERED N OF PUERTO RICO
DIPS INTO THE CENTRAL CARIBBEAN TO NEAR 16N69W. UPPER LEVEL
DIFFLUENCE BETWEEN THIS FEATURE AND THE UPPER LEVEL HIGH IN THE
W CARIBBEAN IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS ACROSS
JAMAICA...WRN CUBA...AND HISPANIOLA. THIS ACTIVITY IS ALSO
ENHANCED BY SURFACE CONVERGENCE NEAR A SURFACE TROUGH N OF THE
BAHAMAS. AN UPPER LEVEL RIDGE CENTERED E OF THE LESSER ANTILLES
NEAR 17N47W DOMINATES THE ERN CARIBBEAN. SLY FLOW ALOFT AROUND
THE UPPER RIDGE IS DRAWING TROPICAL MOISTURE NWD TO SUPPORT
SHOWERS/THUNDERSTORMS IN THE FAR SE CARIBBEAN S OF 12N E OF 67W
NEAR THE ITCZ. MODERATE TO FRESH TRADEWINDS ARE ACROSS MUCH OF
THE BASIN WITH STRONGER WINDS NEAR THE COAST OF COLOMBIA.
INTERESTS IN THE LESSER ANTILLES SHOULD MONITOR A BROAD AREA OF
LOW PRESSURE ABOUT 500 MILES E OF THE ISLANDS...SEE SPECIAL
FEATURES ABOVE.

ATLANTIC OCEAN...
SCATTERED SHOWERS/THUNDERSTORMS ARE ACROSS THE W ATLC NW OF A
LINE FROM 32N73W 27N76W 23N79W IMPACTING WRN CUBA...NW
BAHAMAS...AND THE FLORIDA PENINSULA. THIS ACTIVITY IS SUPPORTED
BY SURFACE CONVERGENCE NEAR A SURFACE TROUGH EXTENDING FROM NEAR
HOBE SOUND FLORIDA NEAR 27N80W TO 31N78W. THE SHOWERS ACTIVITY
IS ALSO SUPPORTED BY UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER
LEVEL TROUGH OVER THE ERN CONUS AND A SHORTWAVE UPPER LEVEL
RIDGE THAT EXTENDS ACROSS S FLORIDA TO NEAR 31N73W. ISOLATED
SHOWERS/THUNDERSTORMS ARE ALSO IMPACTING THE SE BAHAMAS AND AN
AREA TO THE E FROM 20N-29N BETWEEN 65W-72W. THIS ACTIVITY IS
SUPPORTED BY SURFACE CONVERGENCE NEAR A SURFACE TROUGH EXTENDING
FROM 22N73W TO 29N70W. UPPER LEVEL DIFFLUENCE BETWEEN THE
SHORTWAVE RIDGE EXTENDING FROM S FLORIDA AND AN UPPER LEVEL
TROUGH TO THE E WITH AXIS ALONG 30N57W 27N66W 16N69W IS ALSO
ENHANCING THIS SHOWER ACTIVITY AS WELL AS ISOLATED SHOWERS FROM
28N-32N BETWEEN 55W-64W. THE REMAINDER OF THE ATLC IS DOMINATED
BY A BROAD SURFACE RIDGE ANCHORED BY A PAIR OF 1027 MB HIGHS
NEAR 35N53W AND 39N35W. IN THE UPPER LEVELS...A BROAD UPPER
LEVEL RIDGE DOMINATES S OF 24N CENTERED NEAR 17N47W. AN UPPER
LEVEL TROUGH IS N OF THIS RIDGE WITH A LATERAL AXIS ALONG 27N E
OF 45W.

$$
WALTON





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