[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 292344
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT TUE SEP 29 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...
LOW AMPLITUDE E ATLC TROPICAL WAVE PREVIOUSLY ALONG 20W HAS BEEN
MOVED AHEAD TO 24W S OF 13N MOVING W NEAR 15 KT. WWD RELOCATION
IS BASED ON BETTER ALIGNMENT WITH A DEEP LAYER MOISTURE MAXIMUM
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY...AS WELL AS
LOW/MID-LEVEL CYCLONIC FLOW EVIDENT IN SATELLITE IMAGERY AND
SATELLITE DERIVED WINDS. A LARGE AREA OF SAHARAN DUST IS N OF
THE WAVE AXIS MAINTAINING ITS LOW AMPLITUDE. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS FROM 10N-11N BETWEEN
23W-26W...AND FROM 5N-8N BETWEEN 25W-28W.

TROPICAL WAVE IS ALONG 42W S OF 17N MOVING W NEAR 15 KT. THE
WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN
TOTAL PRECIPITABLE WATER IMAGERY. A HIGH AMPLITUDE INVERTED-V
STRUCTURE IS SEEN IN THE LOW-LEVEL CLOUD PATTERN EVIDENT IN
SATELLITE IMAGERY AND SATELLITE DERIVED WINDS. ISOLATED MODERATE
CONVECTION IS FROM 19N-21N BETWEEN 39W-42W. SCATTERED
MODERATE/STRONG CONVECTION IS FROM 7N-11N BETWEEN 39W-48W. THIS
ACTIVITY IS ALSO ENHANCED BY DIFFLUENT FLOW ALOFT.

...THE ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 13N17W 10N22W 8N30W 12N45W
9N61W. ISOLATED MODERATE CONVECTION IS ALONG THE AXIS BETWEEN
30W-35W. A SURFACE TROUGH IS EMBEDDED WITHIN THE ITCZ ALONG 50W
FROM 6N-13N. NO DEEP CONVECTION IS CURRENTLY ASSOCIATED WITH THE
TROUGH.

...DISCUSSION...

THE GULF OF MEXICO...
AS OF 2100 UTC...A COLD FRONT EXTENDS ACROSS THE CENTRAL GULF
FROM TAMPA FLORIDA NEAR 28N83W ALONG 26N89W TO THE TEXAS COAST
TO 28N97W NEAR CORPUS CRISTI. ISOLATED SHOWERS/THUNDERSTORMS ARE
BEHIND THE FRONT N OF 26N BETWEEN 87W-91W...AND ALONG THE
FRONTAL ZONE BETWEEN 91W-97W. THE SRN GULF REMAINS FAIRLY CALM
EXCEPT FOR A FEW ISOLATED SHOWERS ACROSS THE STRAITS OF FLORIDA.
IN THE UPPER LEVELS...AN UPPER LEVEL RIDGE COVERS THE SRN GULF
CENTERED W OF MEXICO NEAR 21N107W. A BROAD UPPER LEVEL TROUGH
COVERS THE NRN GULF SUPPORTING THE COLD FRONT. STRONG SUBSIDENCE
IS AHEAD OF THE FRONTAL SYSTEM SUPPORTING THE FAIR WEATHER
ACROSS THE SRN GULF. EXPECT THE ERN PORTION OF THE COLD FRONT TO
CONTINUE TO DIP SE ACROSS S FLORIDA THROUGH WED AS THE WRN
PORTION LIFTS TO THE N.

THE CARIBBEAN SEA...
MOST OF THE CARIBBEAN IS FAIRLY CALM TONIGHT WITH THE EXCEPTION
OF SOME ISOLATED SHOWERS/THUNDERSTORMS OVER CUBA N OF 21N
BETWEEN 74W-84W. ISOLATED SHOWERS/THUNDERSTORMS ARE ALSO ACROSS
HONDURAS AND NICARAGUA FROM 13N-17N W OF 82W. IN THE UPPER
LEVELS...AN UPPER LEVEL RIDGE EXTENDS FROM THE SRN GULF AND
COVERS THE WRN CARIBBEAN W OF 73W. A SECOND UPPER LEVEL RIDGE
COVERS THE ERN CARIBBEAN CENTERED OVER VENEZUELA NEAR 9N65W.
MOIST SWLY FLOW ALOFT AROUND THIS RIDGE IS SUPPORTING CLOUDINESS
ACROSS THE ERN CARIBBEAN WITH A FEW ISOLATED SHOWERS E OF 72W.
MODERATE TO FRESH TRADE WINDS ARE ACROSS MUCH OF THE BASIN WITH
STRONGER WINDS ACROSS THE ERN CARIBBEAN.

THE ATLANTIC OCEAN...
AS OF 2100 UTC...A COLD FRONT ENTERS THE DISCUSSION AREA NEAR
32N73W TO THE FLORIDA COAST NEAR CAPE CANAVERAL AT 29N81W.
ISOLATED SHOWERS/THUNDERSTORMS ARE WITHIN 75  NM AHEAD OF THE
FRONT. A PRE-FRONTAL SURFACE TROUGH IS AHEAD OF THE FRONT FROM
32N68W TO THE NW BAHAMAS NEAR 25N77W. ISOLATED
SHOWERS/THUNDERSTORMS ARE WITHIN 400 NM AHEAD OF THE TROUGH.
THIS SHOWER ACTIVITY IS ENHANCED BY DIFFLUENT FLOW ALOFT
BETWEEN AN UPPER LEVEL TROUGH ACROSS THE ERN CONUS AND WRN ATLC
WHICH SUPPORTS THE FRONT AND AN UPPER LEVEL RIDGE WITH AXIS FROM
32N61W TO HISPANIOLA NEAR 20N73W. A WEAK 1018 MB SURFACE HIGH IS
NEAR 25N54W. TO THE S...A SURFACE TROUGH EXTENDS FROM 15N49W TO
19N50W. SURFACE CONVERGENCE NEAR THE TROUGH IS SUPPORTING
ISOLATED SHOWERS ALONG THE TROUGH AXIS. UPPER DIFFLUENT FLOW
BETWEEN AN UPPER LEVEL TROUGH WITH AXIS ALONG 60W AND AN UPPER
LEVEL RIDGE CENTERED NEAR 13N51W IS SUPPORTING MORE ISOLATED
SHOWERS IN THE VICINITY OF THE SURFACE TROUGH FROM 15N-27N
BETWEEN 50W-60W. A SECOND COLD FRONT DIPS INTO THE AREA FROM
32N25W TO 28N33W. ISOLATED SHOWERS/THUNDERSTORMS ARE WITHIN 100
NM SE OF THE FRONT. THE REMAINDER OF THE THE ATLC IS DOMINATED
BY A 1020 MB SURFACE HIGH NEAR 26N23W. IN THE UPPER LEVELS...A
BROAD UPPER LEVEL TROUGH DOMINATES N OF 12N E OF 44W. DIFFLUENT
FLOW BETWEEN THIS UPPER TROUGH AND THE AFOREMENTIONED UPPER HIGH
NEAR 13N51W IS ENHANCING CONVECTION NEAR THE TROPICAL WAVE ALONG
42W. SEE ABOVE. A LARGE AREA OF SAHARAN DUST COVERS THE ERN ATLC
E OF 40W.

$$
WALTON






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