[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 101740
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU SEP 10 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.

...SPECIAL FEATURES...

HURRICANE FRED IS CENTERED NEAR 16.8N 35.1W AT 10/1500 UTC OR
ABOUT 640 NM W OF THE CAPE VERDE ISLANDS MOVING NW AT 6 KT.
ESTIMATED CENTRAL PRESSURE IS 974 MB. MAXIMUM SUSTAINED WINDS
HAVE DECREASED TO 85 KT WITH GUSTS TO 105 KT. FURTHER WEAKENING
IS FORECAST DURING THE NEXT COUPLE DAYS. SCATTERED STRONG
CONVECTION IS FROM 16N-18N BETWEEN 34W-36W. SCATTERED MODERATE
CONVECTION IS FROM 18N-20N BETWEEN 31W-37W. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC
FOR MORE DETAILS.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 73W S OF 18N MOVING W NEAR 15 KT. THE
WAVE COINCIDES WITH A NARROW SURGE OF DEEP LAYER MOISTURE AND
FOLLOWS A BROAD MAXIMUM OBSERVED IN TOTAL PRECIPITABLE WATER
IMAGERY. THE NORTHERN PORTION OF THE WAVE LIES UNDER DRY
SUBSIDENT AIR WHICH IS CURRENTLY INHIBITING DEEP CONVECTION NEAR
THE WAVE AXIS.

...ITCZ...

THE ITCZ AXIS IS CENTERED ALONG 12N17W 11N22W 15N28W 12N33W
10N50W 8N61W. ISOLATED MODERATE/STRONG CONVECTION IS FROM 6N-15N
BETWEEN 13W-21W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION
IS WITHIN 50 NM EITHER SIDE OF THE AXIS BETWEEN 35W-47W.

...DISCUSSION...

GULF OF MEXICO...
AS OF 1500 UTC...A SURFACE TROUGH LINES THE NW GULF OF MEXICO
COASTLINE EXTENDING FROM THE LOUISIANA COAST NEAR 29N92W ALONG
THE TEXAS COAST TO 28N96W CONTINUING S TO 24N97W. SURFACE
CONVERGENCE NEAR THE TROUGH IS SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS ACROSS THE W AND N CENTRAL GULF FROM
25N-30N W OF 87W...AND S OF 25N W OF 95W. A SECOND SURFACE
TROUGH IS IN THE SE GULF EXTENDING FROM 26N83W THROUGH THE
YUCATAN CHANNEL TO 19N86W. MOST OF THE ASSOCIATED SHOWERS ARE SE
OF THE BASIN OVER CUBA. HOWEVER...KEY WEST FLORIDA RADAR AND
RECENT LIGHTNING RADAR INDICATE ISOLATED SHOWERS/THUNDERSTORMS S
OF 26N E OF 85W. IN THE UPPER LEVELS...NWLY TO NLY FLOW AROUND
AN UPPER LEVEL RIDGE CENTERED W OF MEXICO NEAR 22N113W COVERS
THE MAJORITY OF THE GULF. THE W SIDE OF AN UPPER LEVEL TROUGH
DIPS ACROSS THE FLORIDA PENINSULA ASSOCIATED WITH AN UPPER LEVEL
LOW OVER VIRGINIA. EXPECT SHOWERS/THUNDERSTORMS TO CONTINUE
ACROSS THE BASIN AS THE TROUGH IN THE SE GULF DRIFTS NW AND A
COLD FRONT WILL MOVE ACROSS TEXAS APPROACH THE NW GULF WATERS
FRI.

CARIBBEAN SEA...
A SURFACE TROUGH EXTENDS FROM THE SE GULF OF MEXICO NEAR 26N83W
INTO THE NW CARIBBEAN TO 19N86W. SURFACE CONVERGENCE NEAR THE
TROUGH IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS FROM
20N-23N BETWEEN 80W-85W INCLUDING WRN CUBA. THIS ACTIVITY IS
ENHANCED BY UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER LEVEL RIDGE
OVER THE GULF AND AN UPPER LEVEL TROUGH EXTENDING FROM THE NW
BAHAMAS ACROSS CENTRAL CUBA TO COSTA RICA. MOIST SWLY FLOW
AROUND THE BASE OF THE UPPER TROUGH IS SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS IN THE SW CARIBBEAN FROM 10N-14N BETWEEN
78W-82W. THE FLOW ALOFT TURNS WLY OVER THE ERN CARIBBEAN
CONTINUING TO DRAW ENOUGH MOISTURE TO SUPPORT HIGH CIRRUS CLOUDS
BETWEEN 13N-17N. DRY AIR ALOFT IS ON EITHER SIDE OF THIS BELT OF
MOSITURE WHICH IS INHIBITING DEEP CONVECTION NEAR THE TROPICAL
WAVE ALONG 73W. MODERATE TO FRESH TRADEWINDS ARE ACROSS MUCH OF
THE BASIN BECOMING STRONG IN THE ERN CARIBBEAN. EXPECT THE
TROUGH IN THE NW CARIBBEAN TO LIFT TO THE NW...AND THE TROPICAL
WAVE ALONG 73W TO CONTINUE TO MOVE WWD.

ATLANTIC OCEAN...
A SURFACE TROUGH ENTERS THE DISCUSSION AREA NEAR 32N72W
CONTINUING ALONG 29N76W TO THE S FLORIDA COAST NEAR 26N80W.
SCATTERED SHOWERS/THUNDERSTORMS ARE WITHIN 300 NM SE OF THE
TROUGH AXIS. SHOWERS HAVE PERSISTED OVER THIS AREA GENERATING
LARGE AMOUNTS OF PRECIPITATION OVER SOME PORTIONS. AS OF 10/1200
UTC...FREEPORT BAHAMAS REPORTED 3.21 INCHES OF RAIN OVER THE
PAST 24 HOURS. THE SHOWER ACTIVITY IS ENHANCED BY UPPER LEVEL
DIFFLUENCE AROUND THE E SIDE OF AN UPPER LEVEL TROUGH EXTENDING
FROM AN UPPER LEVEL LOW OVER VIRGINIA CONTINUING DOWN THE ERN
UNITED STATES COASTLINE ACROSS CENTRAL CUBA TO THE SW CARIBBEAN.
A 1015 MB SURFACE LOW IS N OF PUERTO RICO NEAR 21N65W. THE LOW
IS SUPPORTED BY AN UPPER LEVEL LOW NEAR 26N65W. LOW-LEVEL
CONVERGENCE NEAR THE SURFACE LOW IS SUPPORTING ISOLATED
SHOWERS/POSSIBLE THUNDERSTORMS FROM 19N-27N BETWEEN 61W-68W. A
WEAK 1020 MB SURFACE HIGH IS N OF THE SURFACE LOW CENTERED NEAR
29N60W. FARTHER E...A SURFACE TROUGH EXTENDS FROM 15N48W TO
24N46W. ISOLATED SHOWERS ARE ALONG THE TROUGH AXIS. A SECOND
SURFACE TROUGH EXTENDS FROM 28N50W TO 31N45W. NO SHOWERS ARE
CURRENTLY ASSOCIATED WITH THIS TROUGH. ELSEWHERE ACROSS THE
ATLC...A SURFACE RIDGE BUILDS E OF 40W. IN THE UPPER LEVELS...AN
UPPER LEVEL HIGH IS CENTERED NEAR 27N53W. AN UPPER LEVEL TROUGH
EXTENDS TO THE E ALONG 32N34W TO 18N52W. ANOTHER UPPER LEVEL
RIDGE DOMINATES THE TROPICAL AND ERN ATLC CENTERED E OF THE CAPE
VERDE ISLANDS NEAR 17N20W SUPPORTING CONVECTION ALONG THE ITCZ
AND HURRICANE FRED.

$$
WALTON



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