[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 122358
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SAT SEP 12 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
2330 UTC.

...SPECIAL FEATURES...

TROPICAL STORM FRED HAS BEEN DOWNGRADED TO A TROPICAL DEPRESSION
AS OF 12/2100 UTC. TROPICAL DEPRESSION FRED IS CENTERED NEAR
17.7N 33.7W OR ABOUT 565 NM W OF THE CAPE VERDE ISLANDS DRIFTING
N NEAR 1 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1005 MB.
MAXIMUM SUSTAINED WINDS HAVE DECREASED TO 30 KT WITH GUSTS TO 40
KT. ONLY A SMALL AREA OF SCATTERED MODERATE/ISOLATED STRONG
CONVECTION REMAINS TO THE N OF THE CENTER FROM 20N-22N BETWEEN
33W-34W. FRED IS FORECAST TO BE A REMNANT LOW IN LESS THAN 24
HRS. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 21W/22W S OF 19N MOVING W NEAR 10 KT. A
1010 MB LOW IS ANALYZED ALONG THE WAVE AXIS NEAR 13N. SATELLITE
IMAGERY AND SATELLITE DERIVED WINDS INDICATE A BROAD AREA OF
LOW/MID-LEVEL CYCLONIC TURNING IN THE VICINITY OF THE WAVE AXIS.
THE WAVE ALSO COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS NEAR THE LOW CENTER FROM
12N-14N BETWEEN 21W-23W. SCATTERED STRONG CONVECTION IS FROM
15N-18N BETWEEN 23W-25W.

TROPICAL WAVE IS ALONG 87W S OF 19N MOVING W NEAR 15 KT. THE
WAVE COINCIDES WITH A BROAD AREA OF DEEP LAYER MOISTURE OBSERVED
IN TOTAL PRECIPITABLE WATER IMAGERY. MODERATELY DRY AIR ALOFT IS
CURRENTLY INHIBITING ANY DEEP CONVECTION NEAR THE WAVE.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 15N17W 10N23W 9N40W 10N51W
11N63W. ISOLATED MODERATE/STRONG CONVECTION IS WITHIN 180 NM
EITHER SIDE OF THE AXIS BETWEEN 55W-63W.

...DISCUSSION...

GULF OF MEXICO...
SCATTERED SHOWERS/THUNDERSTORMS REMAIN ACROSS THE WRN GULF
TONIGHT W OF 87W WITH ISOLATED SHOWERS/THUNDERSTORMS IN THE N
CENTRAL GULF. AS OF 2100 UTC...THE SHOWER ACTIVITY IS ENHANCED
BY LOW-LEVEL CONVERGENCE NEAR A 1005 MB SURFACE LOW OFF THE
TEXAS COAST NEAR 28N96W...AND A STATIONARY FRONT HUGGING THE
GULF STATES COASTLINE EXTENDING FROM THE LOW CENTER ALONG 29N93W
29N88W 30N83W AND ACROSS N FLORIDA TO A WEAKER 1011 MB SURFACE
LOW NEAR 30N80W. A WEAK TROUGH EXTENDS FROM THE LOW OFF THE
TEXAS COAST EXTENDING FROM 28N96W TO 22N96W. THE LOW/FRONTAL
SYSTEM IS SUPPORTED UP AN UPPER LEVEL TROUGH ACROSS THE SW
UNITED STATES EXTENDING INTO THE WRN GULF. AN UPPER LEVEL HIGH
COVERS THE CENTRAL AND ERN GULF CENTERED NEAR 25N85W. UPPER
LEVEL DIFFLUENCE BETWEEN THESE FEATURES IS ALSO ENHANCING THE
SHOWERS/THUNDERSTORMS ACROSS THE BASIN.

CARIBBEAN SEA...
MOST OF THE CARIBBEAN REMAINS CALM THIS EVENING DUE TO MID/UPPER
LEVEL DRY AIR...EXCEPT FOR ISOLATED SHOWERS/THUNDERSTORMS ACROSS
THE NRN ISLANDS N OF 17N FROM BETWEEN ERN HISPANIOLA TO WRN
CUBA. THE SHOWER ACTIVITY IS ENHANCED BY UPPER LEVEL DIFFLUENCE
BETWEEN THE UPPER LEVEL RIDGE ACROSS THE GULF AND WRN ATLC AND
AN UPPER LEVEL LOW N OF PUERTO RICO NEAR 21N65W. HIGH LEVEL
CLOUDS ARE ACROSS THE BASIN S OF 13N DUE TO SLY FLOW ALOFT
SHIFTING TO WLY FLOW ALOFT DRAWING TROPICAL MOISTURE N AND E.
SURFACE CONVERGENCE NEAR THE ITCZ IS SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS S OF 12N W OF 78W AFFECTING COSTA RICA AND
PANAMA. SURFACE CONVERGENCE NEAR A 1009 MB LOW OVER NRN COLOMBIA
NEAR 9N75W IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS S OF
11N BETWEEN 70W-75W. A FEW ISOLATED SHOWERS ARE ALSO AFFECTING
THE SRN LESSER ANTILLES. MODERATE TO FRESH TRADEWINDS ARE ACROSS
MUCH OF THE BASIN. EXPECT THE TROPICAL WAVE ALONG 87W TO MOVE W
OF CENTRAL AMERICA LATER TONIGHT.

ATLANTIC OCEAN...
A FEW ISOLATED SHOWERS/POSSIBLE THUNDERSTORMS REMAIN ACROSS THE
WRN ATLC W OF 72W TO THE FLORIDA COAST IN ASSOCIATION WITH A
WEAK 1011 MB LOW OFF THE N FLORIDA COAST NEAR 30N80W...AND A
STATIONARY FRONT EXTENDING ALONG THE GULF COAST ACROSS N FLORIDA
TO THE WEAK LOW CONTINUING TO 31N77W. THE SHOWERS ARE ALSO
ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL RIDGE
OVER THE GULF EXTENDING OVER THE WRN ATLC W OF 72W...AN UPPER
LEVEL TROUGH N OF THE RIDGE CENTERED OVER NEW ENGLAND...AND AN
UPPER LEVEL LOW N OF PUERTO RICO NEAR 21N65W. A WEAK 1018 MB
SURFACE HIGH IS TO THE E NEAR 27N62W. FARTHER E...A STATIONARY
FRONT DIPS INTO THE DISCUSSION AREA NEAR 32N60W CONTINUING ALONG
29N49W 32N36W EXTENDING NE OUT OF THE AREA. ISOLATED SHOWERS ARE
ALONG THE FRONT WITH AN AREA OF SCATTERED SHOWERS/THUNDERSTORMS
FROM 29N-31N BETWEEN 55W-58W. THIS ACTIVITY IS ALSO ENHANCED BY
UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER HIGH NEAR 27N55W AND AN
UPPER LEVEL TROUGH N OF 20N WITH AXIS ALONG 40W. THE UPPER LEVEL
TROUGH IS ALSO SUPPORTING A SURFACE TROUGH THAT HAS BECOME
EMBEDDED IN THE ITCZ ALONG 19N51W TO 10N52W. AN UPPER LEVEL
RIDGE COVERS THE ERN ATLC CENTERED OFF THE COAST OF AFRICA NEAR
19N20W ENHANCING CONVECTION NEAR THE TROPICAL WAVE ALONG
21W/22W.

$$
WALTON





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