[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 132340
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN SEP 13 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.

...SPECIAL FEATURES...
AN AREA OF SHOWERS/THUNDERSTORMS TO THE N OF A 1009 MB SURFACE
LOW NEAR 18N35W...THE REMNANT CIRCULATION OF FRED...HAS
INCREASED OVER THE PAST FEW HOURS. NUMEROUS STRONG CONVECTION IS
FROM 19N-23N BETWEEN 34W-36W. UPPER LEVEL WINDS REMAIN
UNFAVORABLE FOR REDEVELOPMENT INTO A TROPICAL CYCLONE.
HOWEVER...IF CONVECTION CONTINUES TO PERSIST AND BECOMES BETTER
ORGANIZED REGENERATION IS POSSIBLE. THERE IS NOW A MEDIUM
CHANCE...30 TO 50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HRS.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 60W/61W S OF 15N. THIS WAVE HAS
PREVIOUSLY BEEN ANALYZED AS A SURFACE TROUGH THAT ORIGINALLY
FORMED AS A FRACTURE OF A TROPICAL WAVE SEVERAL DAYS AGO. THE
TROUGH STALLED DUE TO THE CIRCULATION OF FRED AND THE PRESENCE
OF AN UPPER LEVEL TROUGH BEFORE REGAINING WWD MOVEMENT AND IS
NOW RE-ANALYZED AS A TROPICAL WAVE. BASED ON THE PREVIOUS 24 HR
TROUGH POSITION THE WAVE IS MOVING W 15-20 KT. THE WAVE
COINCIDES WITH A LOW-AMPLITUDE DEEP LAYER MOISTURE MAXIMUM
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED MODERATE
CONVECTION IS FROM 11N-13N BETWEEN 57W-60W.

TROPICAL WAVE IS ALONG 95W S OF 19N MOVING W NEAR 20 KT. WAVE IS
MAINLY IN THE E PACIFIC REGION GENERATING SCATTERED
SHOWERS/THUNDERSTORMS. NO ASSOCIATED SHOWER ACTIVITY IS IN THE
BAY OF CAMPECHE. REFER TO THE TWDEP FOR MORE DETAILS.
...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 18N17W THROUGH A 1012 MB LOW
NEAR 14N22W CONTINUING ALONG 9N30W 7N40W 10N50W 12N57W 10N65W.
SCATTERED MODERATE CONVECTION IS FROM 14N-16N BETWEEN 23W-25W
NEAR THE SURFACE LOW. ISOLATED MODERATE CONVECTION IS WITHIN 150
NM S OF THE AXIS BETWEEN 26W-34W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 2100 UTC...A STATIONARY FRONT LINES THE N GULF FROM N
FLORIDA NEAR 29N83W ALONG 31N87W 30N90W TO A 1005 MB LOW NEAR
HOUSTON TEXAS AT 30N96W. A SURFACE TROUGH EXTEND S FROM THE LOW
CENTER ALONG 26N93W 21N94W. THE SYSTEM IS SUPPORTED BY A
SHORTWAVE UPPER LEVEL TROUGH OVER TEXAS EMBEDDED IN A BROAD
UPPER LEVEL TROUGH OVER NRN MEXICO. ISOLATED SHOWERS/
THUNDERSTORMS ARE FROM 22N-26N BETWEEN 90W-93W. RECENT LIGHTNING
DATA INDICATES NUMEROUS SHOWERS/THUNDERSTORMS IN THE CENTRAL
GULF FROM 25N-29N BETWEEN 87W-90W. ISOLATED
SHOWERS/THUNDERSTORMS ARE ALSO ACROSS THE ERN GULF FROM 22N-28N
E OF 87W. THIS ACTIVITY IS ENHANCED BY SURFACE CONVERGENCE AHEAD
OF THE TROUGH AND FRONT AS WELL AS UPPER LEVEL DIFFLUENCE
BETWEEN THE UPPER LEVEL TROUGH OVER MEXICO AND TEXAS AND AN
UPPER LEVEL RIDGE DOMINATING THE ERN GULF CENTERED OVER WRN CUBA
NEAR 23N83W. BEHIND THE SURFACE TROUGH...STRONG SUBSIDENCE AND
DRY AIR ALOFT ARE SUPPORTING GENERALLY FAIR WEATHER W OF 93W.
EXPECT LITTLE CHANGE OVER THE NEXT 24 HRS.

CARIBBEAN SEA...
MOST OF THE CARIBBEAN REMAINS FAIRLY CALM TONIGHT WITH DRY AIR
ALOFT ACROSS MUCH OF THE BASIN. ISOLATED SHOWERS/POSSIBLE
THUNDERSTORMS ARE ACROSS THE NRN CARIBBEAN N OF 17N BETWEEN
69W-80W INCLUDING PORTIONS OF HISPANIOLA AND JAMAICA. SCATTERED
SHOWERS/THUNDERSTORMS ARE ACROSS CUBA N 19N BETWEEN 75W-84W.
BOTH OF THESE AREAS OF ACTIVITY ARE ENHANCED BY UPPER LEVEL
DIFFLUENCE BETWEEN AN UPPER LEVEL RIDGE CENTERED OVER W CUBA
NEAR 23N83W AND AN UPPER LEVEL LOW N OF THE LEEWARD ISLANDS NEAR
20N63W. A FEW ISOLATED SHOWERS ARE S OF 14N BETWEEN 74W-84W DUE
TO SURFACE CONVERGENCE NEAR THE E PACIFIC ITCZ. MODERATE TRADE
WINDS ARE ACROSS THE BASIN WITH STRONGER WINDS NEAR THE COAST OF
COLOMBIA. EXPECT SHOWER ACTIVITY TO INCREASE OVER THE WINDWARD
ISLANDS AS A TROPICAL WAVE ALONG 60W/61W MOVES WWD INTO THE E
CARIBBEAN.

ATLANTIC OCEAN...
AS OF 2100 UTC...A 1011 MB LOW IS OFF THE N FLORIDA COAST NEAR
30N79W. A STATIONARY FRONT EXTENDS THROUGH THE LOW FROM 31N75W
TO THE FLORIDA COAST NEAR 29N81W CONTINUING ALONG THE NRN GULF
OF MEXICO. SURFACE CONVERGENCE AHEAD OF THE FRONT IS SUPPORTING
SCATTERED SHOWERS/THUNDERSTORMS N OF 79N W OF 75W AFFECTING THE
WRN BAHAMAS...CUBA...AND FLORIDA. ISOLATED SHOWERS/THUNDERSTORMS
ARE N OF 25N BETWEEN 62W-75W. THESE AREAS OF ACTIVITY ARE ALSO
ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL RIDGE
CENTERED OVER WRN CUBA NEAR 23N83W...AN UPPER LEVEL TROUGH N OF
33N OVER THE NW ATLC...AND AN UPPER LEVEL LOW N OF THE LEEWARD
ISLANDS NEAR 20N63W. A WEAK 1017 MB SURFACE HIGH IS CENTERED
NEAR 25N60W. TO THE NE OF THE HIGH A WARM FRONT DIPS INTO THE
DISCUSSION AREA EXTENDING ALONG 29N54W 32N55W TO A SURFACE LOW
WELL N OF THE AREA. ISOLATED SHOWERS/POSSIBLE THUNDERSTORMS ARE
E OF THE FRONT N OF 28N BETWEEN 50W-54W. THE ACTIVITY IS
ALSO ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL
HIGH NEAR 26N53W AND THE AFOREMENTIONED UPPER LEVEL TROUGH OVER
THE NW ATLC. A DYING STATIONARY FRONT CLIPS THE AREA EXTENDING
ALONG 32N35W 39N40W 31N44W. NO SHOWERS ARE CURRENTLY ASSOCIATED
WITH THE FRONT. ELSEWHERE ACROSS THE ATLC...A 1009 MB
LOW...REMNANTS OF FRED...REMAINS THE DOMINANT FEATURE. SEE
SPECIAL FEATURES ABOVE. IN THE UPPER LEVELS...AN UPPER LEVEL
TROUGH IS ALONG 16N47W TO 28N30W. STRONG SWLY FLOW ALOFT ALONG
THE E SIDE OF THIS UPPER TROUGH CONTINUES TO PROVIDE A SHEER
ENVIRONMENT FOR THE REMNANTS OF FRED. AN UPPER LEVEL HIGH IS OFF
THE COAST OF AFRICA NEAR 20N17W ENHANCING CONVECTION NEAR THE
CAPE VERDE ISLANDS.

$$
WALTON






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