[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 171745
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU SEP 17 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1700 UTC.

...TROPICAL WAVES...

TROPICAL WAVE PREVIOUSLY ALONG 23W/24W HAS BEEN RELOCATED ALONG
19W S OF 18N MOVING W 10-15 KT. WHILE A BURST OF CONVECTION WITH
ASSOCIATED CYCLONIC FLOW DID EMERGE OFF THE AFRICAN COAST
YESTERDAY...IT APPEARS THAT THE ACTUAL WAVE AXIS FOLLOWED BEHIND
IT. A 17/0000 UPPER AIR SOUNDING FROM DAKAR SENEGAL INDICATES A
STRONGER AND MORE CONCLUSIVE SURFACE WIND SHIFT INDICATING THE
WAVE PASSAGE...JUSTIFYING THE RELOCATION. SCATTERED STRONG
CONVECTION IS FROM 13N-15N BETWEEN 18W-20W. ISOLATED MODERATE
CONVECTION IS FROM 8N-11N BETWEEN 17W-20W.

TROPICAL WAVE IS ALONG 83W S OF 19N MOVING W NEAR 12 KT. THE
WAVE LIES WITHIN A BROAD AREA OF DEEP LAYER MOISTURE. NO DEEP
CONVECTION IS CURRENTLY ASSOCIATED WITH THE WAVE.
HOWEVER...ISOLATED SHOWERS ARE WITHIN 100 NM OF THE WAVE AXIS.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 12N20W 9N25W 11N32W 7N42W 9N52W
10N62W. ISOLATED MODERATE CONVECTION IS FROM 6N-10N BETWEEN
25W-40W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 1500 UTC...A COLD FRONT EXTENDS THROUGH LOUISIANA TO NEAR
29N92W INTO THE NW GULF EXTENDING TO SRN TEXAS NEAR 27N97W.
SCATTERED SHOWERS/THUNDERSTORMS ARE WITHIN 75 NM AHEAD OF THE
FRONT. A PRE-FRONTAL SURFACE TROUGH IS ANALYZED FROM THE FLORIDA
PANHANDLE NEAR 30N86W TO 23N92W. SCATTERED SHOWERS/THUNDERSTORMS
ARE WITHIN 50 NM EITHER SIDE OF THE TROUGH AXIS. ISOLATED
SHOWERS ALSO LINE THE SW COAST OF FLORIDA FROM 25N-28N BETWEEN
82W-83W. THE FRONTAL SYSTEM IS SUPPORTED BY AN UPPER LEVEL
TROUGH ACROSS THE CENTRAL UNITED STATES EXTENDING ACROSS THE WRN
AND CENTRAL GULF. THE SHOWER ACTIVITY ALONG THE SURFACE TROUGH
IS ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER LEVEL
TROUGH OVER THE CENTRAL CONUS AND AN UPPER LEVEL RIDGE OVER THE
SE GULF AND INTO THE WRN ATLC.

CARIBBEAN SEA...
THE NW CARIBBEAN REMAINS FAIRLY CALM DUE TO MODERATE DRY AIR
ALOFT AROUND AN UPPER LEVEL RIDGE EXTENDING FROM THE WRN ATLC
INTO THE NW CARIBBEAN. HOWEVER...ISOLATED SHOWERS ARE WITHIN 100
NM OF THE TROPICAL WAVE ALONG 83W...SEE ABOVE. SCATTERED
SHOWERS/THUNDERSTORMS ARE IN THE FAR SW CARIBBEAN S OF 11N
BETWEEN 76W-81W DUE TO SURFACE CONVERGENCE NEAR THE E PACIFIC
ITCZ. ISOLATED SHOWERS/POSSIBLE THUNDERSTORMS ARE IN THE CENTRAL
AND E CARIBBEAN FROM 13N-18N BETWEEN 67W-78W. SCATTERED
SHOWERS/THUNDERSTORMS ARE FROM 12N-17N BETWEEN 63W-66W. BOTH
AREAS OF ACTIVITY ARE ASSOCIATED WITH AN UPPER LEVEL LOW NEAR
15N74W. MODERATE TRADE WINDS REMAIN ACROSS MUCH OF THE BASIN.
EXPECT THE TROPICAL WAVE ALONG 83W TO CONTINUE W AND OUT OF THE
BASIN BY TOMORROW.

ATLANTIC OCEAN...
A SURFACE TROUGH EXTENDS FROM A 1009 MB LOW NEAR 35N69W ENTERING
THE DISCUSSION AREA NEAR 32N71W CONTINUING TO THE CENTRAL
BAHAMAS NEAR 25N76W. ISOLATED SHOWERS ARE WITHIN 75 NM EITHER
SIDE OF THE TROUGH AXIS FROM 23N-28N. SCATTERED SHOWERS/POSSIBLE
THUNDERSTORMS ARE WITHIN 150 NM AHEAD OF THE TROUGH N OF 28N.
SHOWERS ALONG THE TROUGH ARE ALSO SUPPORTED BY UPPER LEVEL
DIFFLUENCE BETWEEN AN UPPER LEVEL TROUGH OVER THE NW ATLC AND AN
UPPER LEVEL RIDGE OVER THE SW ATLC EXTENDING FROM 33N62W ACROSS
THE BAHAMAS AND CUBA TO THE NW CARIBBEAN. A SURFACE
TROUGH...REMNANT OF FRED...IS ANALYZED FROM 21N59W TO 27N61W.
SURFACE CONVERGENCE NEAR THE TROUGH IS SUPPORTING ISOLATED
SHOWERS 21N-26N BETWEEN 59W-63W. AN UPPER LEVEL LOW NEAR 20N53W
IS ALSO ENHANCING THE SHOWERS NEAR THE SURFACE TROUGH AS WELL AS
AN AREA OF SCATTERED SHOWERS/THUNDERSTORMS FROM 20N-26N BETWEEN
50W-56W. THE REMAINDER OF THE ATLC IS DOMINATED BY A BROAD
SURFACE RIDGE ANCHORED BY A 1027 MB HIGH NEAR 35N46W. IN THE
UPPER LEVELS...AN UPPER LEVEL TROUGH DOMINATES THE NE ATLC
CENTERED NEAR 28N26W. A BROAD UPPER LEVEL RIDGE DOMINATES THE
TROPICAL ATLC ENHANCING CONVECTION ALONG THE ITCZ.

$$
WALTON





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