[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 282359
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT MON SEP 28 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 2245 UTC.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 42W S OF 14N MOVING W NEAR 20 KT. THE
WAVE IS ALONG THE ERN EDGE OF A DEEP LAYER MOISTURE MAXIMUM
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. THE WAVE LIES IN A
BROAD AREA OF L0W/MID-LEVEL CYCLONIC FLOW INDICATED BY SATELLITE
IMAGERY AND SATELLITE DERIVED WINDS. A LARGE AREA OF SAHARAN
DUST IS MAINLY N OF 13N AND E OF 40W. HOWEVER...SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS FROM 7N-10N BETWEEN
36W-40W...AND FROM 13N-14N BETWEEN 34W-36W. IT IS LIKELY THAT
THIS ACTIVITY IS ASSOCIATED MORE WITH A DIFFLUENT ZONE ALOFT.

TROPICAL WAVE IS OVER CENTRAL AMERICA ALONG 85W/86W S OF 16N
MOVING W NEAR 20 KT. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS FROM 10N-16N BETWEEN 82W-87W AFFECTING PORTIONS OF
COSTA RICA...NICARAGUA...AND HONDURAS.

...THE ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 9N13W 7N21W 10N34W 8N50W 7N59W.
SCATTERED STRONG CONVECTION IS ALONG THE AFRICA COAST FROM
7N-12N BETWEEN 9W-14W. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS FROM 5N-9N BETWEEN 18W-21W. ISOLATED MODERATE
CONVECTION IS WITHIN 100 NM OF THE AXIS BETWEEN 44W-53W.

...DISCUSSION...

THE GULF OF MEXICO...
AS OF 2100 UTC...A PRE-FRONTAL SURFACE TROUGH EXTENDS ACROSS THE
NW GULF FROM MISSISSIPPI NEAR 30N89W TO ERN TEXAS NEAR 30N95W.
THIS TROUGH IS AHEAD OF A STRONG COLD FRONT THAT EXTENDS ACROSS
MUCH OF THE ERN CONUS. SCATTERED SHOWERS/THUNDERSTORMS ARE
WITHIN 75 NM OF THE TROUGH AXIS. THE REMAINDER OF THE GULF IS
DOMINATED BY A WEAK 1014 MB SURFACE HIGH NEAR 26N94W BRINGING
DRY AND FAIR WEATHER ACROSS THE BASIN. HOWEVER...THE TAIL END OF
A COLD FRONT EXTENDS FROM THE WRN ATLC ACROSS S FLORIDA AND INTO
THE SE GULF FROM FORT MYERS FLORIDA NEAR 27N82W TO 26N86W. NO
SHOWERS ARE CURRENTLY ASSOCIATED WITH THIS PORTION OF THE FRONT.
IN THE UPPER LEVELS...MOST OF THE GULF IS COVERED BY A BROAD
RIDGE CENTERED OVER MEXICO NEAR 23N106W WITH ANOTHER RIDGE
COVERING THE SE GULF CENTERED OVER THE YUCATAN CHANNEL NEAR
21N86W. THE NRN GULF IS COVERED BY AN UPPER LEVEL TROUGH
COVERING THE ENTIRE ERN CONUS EXTENDING FROM AN UPPER LEVEL LOW
OVER THE GREAT LAKES. THIS UPPER LEVEL TROUGH IS SUPPORTING THE
IMPRESSIVE COLD FRONT THAT EXTENDS DOWN THE ERN CONUS AND ACROSS
THE GULF STATES. EXPECT THIS COLD FRONT TO ENTER THE NRN GULF
WATERS BY EARLY TOMORROW.

THE CARIBBEAN SEA...
A TROPICAL WAVE IS OVER CENTRAL AMERICA GENERATING
SHOWERS/THUNDERSTORMS...SEE ABOVE. A FEW SHOWERS/THUNDERSTORMS
ARE ACROSS WRN CUBA FROM 21N-23N BETWEEN 80W-84W. ISOLATED
SHOWERS ARE ACROSS THE SW GULF S OF 15N W OF 77W. THE REMAINDER
OF THE NW AND CENTRAL GULF IS EXPERIENCING GENERALLY FAIR
WEATHER UNDER THE INFLUENCE OF DRY AIR AND SUBSIDENCE ALOFT
ASSOCIATED WITH AN UPPER LEVEL RIDGE CENTERED OVER THE YUCATAN
CHANNEL NEAR 21N86W. SCATTERED SHOWERS/THUNDERSTORMS ARE OVER
HISPANIOLA INFLUENCED BY DIFFLUENT FLOW ALOFT BETWEEN THE UPPER
RIDGE AND A NARROW UPPER LEVEL TROUGH EXTENDING FROM AN UPPER
LEVEL LOW NEAR 27N62W TO WRN HISPANIOLA NEAR 18N69W CONTINUING
TO 11N77W. MOIST SWLY FLOW ALOFT AROUND THE E SIDE OF THIS UPPER
TROUGH AND AROUND ANOTHER UPPER LEVEL RIDGE CENTERED E OF THE
LESSER ANTILLES NEAR 15N55W IS SUPPORTING CLOUDINESS AND
POSSIBLE SHOWERS ACROSS THE ERN CARIBBEAN E OF 72W. FRESH TO
STRONG TRADEWINDS ARE OVER MUCH OF THE BASIN.

THE ATLANTIC OCEAN...
AS OF 2100 UTC...A COLD FRONT EXTENDS ACROSS THE WRN ATLC
ENTERING THE DISCUSSION AREA NEAR 32N71W EXTENDING TO THE NW
BAHAMAS NEAR 26N78W CONTINUING WWD TO S FLORIDA NEAR WEST PALM
BEACH. A PRE-FRONTAL SURFACE TROUGH IS AHEAD OF THE FRONT FROM
28N73W TO 24N77W. SURFACE CONVERGENCE NEAR THE FRONT AND TROUGH
IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS WITHIN 150 NM
AHEAD OF THE FRONT. THIS SHOWER ACTIVITY IS ENHANCED BY UPPER
LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL TROUGH COVERING THE ERN
CONUS AND WRN ATLC N OF 27N W OF 66W AND AN UPPER LEVEL RIDGE S
OF 27N CENTERED OVER THE YUCATAN CHANNEL NEAR 21N86W. A WEAK
1020 MB SURFACE HIGH IS NEAR 25N55W. ANOTHER COLD FRONT LINES
THE DISCUSSION AREA FROM 32N35W TO 30N51W. A PRE-FRONTAL SURFACE
TROUGH IS AHEAD OF THE FRONT FROM 31N34W TO 27N46W. MOST OF THE
SHOWERS ASSOCIATED WITH THIS SYSTEM HAVE NOW DISSIPATED. ANOTHER
SURFACE TROUGH...THE PREVIOUS REMNANTS OF T.D. EIGHT...EXTENDS
FROM 22N45W TO 15N44W. ISOLATED SHOWERS ARE ALONG THE TROUGH
AXIS. ELSEWHERE ACROSS THE ATLC...A 1022 MB SURFACE HIGH
DOMINATES CENTERED NEAR 30N25W. IN THE UPPER LEVELS...A SURFACE
RIDGE IS BETWEEN 45W-65W CENTERED NEAR 15N55W. A BROAD UPPER
LEVEL TROUGH IS BETWEEN 32W-45W. ANOTHER UPPER RIDGE COVERS E OF
32W. DIFFLUENT FLOW BETWEEN THIS UPPER RIDGE AND THE UPPER
TROUGH IS ENHANCING CONVECTION ALONG THE ITCZ AND THE TROPICAL
WAVE ALONG 42W.

$$
WALTON




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