[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 230513
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT WED SEP 23 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0430 UTC.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 41W/42W S OF 18N MOVING WNW 15 KT.
SATELLITE IMAGERY INDICATES A WELL DEFINED INVERTED-V STRUCTURE
IN THE LOW LEVEL CLOUD PATTERN. AN ASCAT PASS FROM 0032 UTC ALSO
CONFIRMS CYCLONIC FLOW IN THE VICINITY OF THE WAVE AXIS. A LARGE
AREA OF SAHARAN DUST IS E OF THE AXIS MAINLY E OF 35W WHICH IS
CURRENTLY CONFINING CONVECTION TO THE ITCZ.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 13N16W 8N22W 7N30W 10N40W 9N50W
11N64W. A BROAD AREA OF MID LEVEL CYCLONIC ROTATION IS ALONG THE
COAST OF W AFRICA AND IS GENERATING A CLUSTER OF SCATTERED
STRONG CONVECTION FROM 13N-15N BETWEEN 17W-19W. SMALL CLUSTERS
OF ISOLATED MODERATE/STRONG CONVECTION ARE WITHIN 100 NM OF THE
AXIS BETWEEN 16W-20W...AND 24W-48W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 0300 UTC...A COLD FRONT EXTENDS ACROSS THE NW GULF FROM
LAKE CHARLES LOUISIANA NEAR 30N93W ALONG 27N96W TO THE SRN TIP
OF TEXAS NEAR 26N97W. A PRE-FRONTAL SURFACE TROUGH IS AHEAD OF
THE FRONT FROM 29N90W ALONG 27N93W TO 24N96W. SURFACE
CONVERGENCE NEAR THE FRONT/TROUGH IS SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS NW OF A LINE FROM 30N87W TO 24N98W. A WEAK
SURFACE TROUGH EXTENDS THROUGH THE YUCATAN PENINSULA FROM 23N85W
TO 18N85W IN THE NW CARIBBEAN. THE TROUGH IS SUPPORTING ISOLATED
SHOWERS/THUNDERSTORMS S OF 23N BETWEEN 86W-88W. A LINE OF
SHOWERS/THUNDERSTORMS PREVIOUSLY INLAND OVER FLORIDA HAS NOW
MOVED OFF THE W COAST OF FLORIDA FROM 24N-29N ALONG 83W. THESE
SHOWERS ARE MOST LIKELY LEFT OVER FROM AFTERNOON HEATING AND
SEABREEZE CONVERGENCE OVER THE PENINSULA. IN THE UPPER
LEVELS...A BROAD UPPER LEVEL RIDGE COVERS THE MAJORITY OF THE
BASIN CENTERED OVER MEXICO NEAR 22N101W. SHOWERS/THUNDERSTORMS
ASSOCIATED WITH THE FRONT IN THE NW GULF ARE ALSO ENHANCED BY
DIFFLUENT FLOW BETWEEN THE UPPER LEVEL RIDGE AND AN UPPER LEVEL
LOW OVER THE CENTRAL CONUS. A SHORTWAVE UPPER LEVEL TROUGH DIGS
E-W ACROSS S FLORIDA AND THE STRAITS OF FLORIDA ENHANCING THE
SHOWERS/THUNDERSTORMS ALONG THE W COAST OF FLORIDA. EXPECT THE
FRONT TO STALL AND BECOME STATIONARY FOR THE NEXT COUPLE OF
DAYS.

CARIBBEAN SEA...
AS OF 0300 UTC...A WEAK SURFACE TROUGH EXTENDS ACROSS THE NW
CARIBBEAN FROM 23N85W TO 18N85W SUPPORTING A FEW ISOLATED
SHOWERS/THUNDERSTORMS FROM 19N-23N W OF 86W. SCATTERED
SHOWERS/THUNDERSTORMS ARE ACROSS CUBA N OF 19N BETWEEN 74W-84W.
ISOLATED SHOWERS/THUNDERSTORMS ARE S AND E OF THIS ACTIVITY FROM
16N-19N BETWEEN 75W-84W...AND N OF 16N BETWEEN 66W-72W AFFECTING
PUERTO RICO AND HISPANIOLA. THESE AREAS OF SHOWERS/THUNDERSTORMS
ARE SUPPORTED BY UPPER LEVEL DIFFLUENT FLOW BETWEEN THE UPPER
RIDGE OVER THE GULF OF MEXICO...A SHORTWAVE E-W UPPER TROUGH
OVER THE BAHAMAS TO THE STRAITS OF FLORIDA EMBEDDED IN A LARGER
AND MORE BROAD UPPER LEVEL TROUGH COVERING THE MAJORITY OF THE
CARIBBEAN WITH AXIS E OF THE LESSER ANTILLES ALONG 59W. ISOLATED
SHOWERS/THUNDERSTORMS ARE ALSO ACROSS THE SW CARIBBEAN S OF 13N
BETWEEN 72W-83W DUE TO SURFACE CONVERGENCE NEAR A 1006 MB LOW
OVER COLOMBIA NEAR 9N74W...AND THE CLOSE PROXIMITY OF THE E
PACIFIC ITCZ. THE REMAINDER OF THE CARIBBEAN REMAINS CALM UNDER
THE INFLUENCE OF DRY AIR ALOFT. FRESH TRADEWINDS ARE ACROSS MUCH
OF THE BASIN.

ATLANTIC OCEAN...
AS OF 0300 UTC...A WEAK SURFACE TROUGH LINES THE E COAST OF
FLORIDA FROM 31N80W TO 27N80W SUPPORTING ISOLATED SHOWERS FROM
28N-32N BETWEEN 77W-80W. ISOLATED SHOWERS/THUNDERSTORMS ARE S OF
22N TO THE NRN CARIBBEAN BETWEEN 66W-81W DUE TO UPPER DIFFLUENT
FLOW AROUND A SHORTWAVE E-W UPPER TROUGH ACROSS THE BAHAMAS
EMBEDDED IN A LARGER AND MORE BROAD UPPER TROUGH ALONG 59W
EXTENDING TO AN UPPER LEVEL LOW NEAR 31N64W. THE UPPER LEVEL LOW
IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS N OF 26N BETWEEN
54W-63W. A FEW ISOLATED SHOWERS ARE ALSO E OF THE UPPER TROUGH
AXIS FROM 17N-20N BETWEEN 54W-58W. A WEAKENING 1012 MB SURFACE
LOW IS NEAR 16N49W. A SURFACE TROUGH EXTENDS THROUGH THE LOW
FROM 21N47W TO 12N50W. SURFACE CONVERGENCE NEAR THE TROUGH IS
SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS FROM 20W-23W BETWEEN
45W-48W...AND A LINE OF ISOLATED SHOWERS FROM 25N40W TO 19N43W.
THE REMAINDER OF THE ATLC IS RELATIVELY CALM UNDER THE INFLUENCE
OF A BROAD SURFACE RIDGE. A BROAD UPPER LEVEL RIDGE DOMINATES
THE BASIN E OF 50W E OF THE UPPER LEVEL TROUGH ALONG 59W. A
LARGE AREA OF SAHARAN DUST IS ACROSS THE ERN ATLC MAINLY E OF
35W.

$$
WALTON






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