[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 290000
TWDAT

TROPICAL WEATHER DISCUSSION...
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU AUG 28 2008

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
2315 UTC.

...SPECIAL FEATURES...
TROPICAL STORM GUSTAV IS CENTERED NEAR 17.9N 77.0W AT 29/0000
UTC OR ABOUT 13 NM WEST OF KINGSTON JAMAICA AND ABOUT 260 NM
EAST-SOUTHEAST OF GRAND CAYMAN MOVING WEST AT 6 KT. MINIMUM
CENTRAL PRESSURE IS 988 MB. MAXIMUM SUSTAINED WIND SPEED IS 60
KT WITH GUSTS TO 75 KT. PLEASE SEE THE LATEST NHC FORECAST/
ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC AND/OR
THE PUBLIC ADVISORY MIATCPAT2/WTNT32 KNHC FOR MORE DETAILS.
GUSTAV IS TRACKING OVER JAMAICA THIS EVENING AND IS FORECAST TO
EMERGE OUT INTO THE OPEN WATERS OF THE NW CARIBBEAN BY TOMORROW.
WITH A WEAK MID-LEVEL RIDGE OVER FLORIDA...ALL MODELS FORECAST
GUSTAV TO CONTINUE GENERALLY WESTWARD FOR THE NEXT DAY OR SO AND
COME UNDER THE INFLUENCE OF ANTICYCLONIC FLOW ALOFT WHICH ALONG
WITH THE WARM WATERS WILL BE FAVORABLE FOR STRENGTHENING.
MODERATE TO STRONG CONVECTION IS FROM 15N-20N BETWEEN 73W-79W
INCLUDING JAMAICA. SIMILAR OUTER BANDS OF CONVECTION ARE ACROSS
HISPANIOLA AND S OF CENTRAL CUBA BETWEEN 78W-81W. GUSTAV IS
EXPECTED TO PRODUCE TOTAL RAINFALL ACCUMULATIONS OF 6 TO 12
INCHES ACROSS JAMAICA AND THE CAYMAN ISLANDS...WITH ISOLATED
MAXIMUM AMOUNTS OF UP TO 25 INCHES POSSIBLE. THESE RAINS WILL
LIKELY PRODUCE LIFE-THREATENING FLASH FLOODS AND MUD SLIDES.
RAINFALL ACCUMULATIONS OF 2 TO 4 INCHES ARE POSSIBLE OVER
SOUTHERN CUBA. RAINFALL WILL BE DIMINISHING OVER HAITI
TONIGHT...WITH AN ADDITIONAL 1 TO 2 INCHES OF RAINFALL POSSIBLE.

TROPICAL STORM HANNA IS CENTERED NEAR 20.7N 60.1W AT 28/2100
UTC OR ABOUT 225 NM NORTHEAST OF THE NORTHERN LEEWARD ISLANDS
MOVING WEST-NORTHWEST AT 10KT. A TURN TOWARD THE NORTHWEST IS
FORECAST OVER THE NEXT COUPLE OF DAYS WITH GRADUAL STRENGTHENING
EXPECTED AS THE CYCLONE WILL MOVE AWAY FROM THE NORTHERN LEEWARD
ISLANDS AND BE CENTERED WELL TO THE NORTHEAST OF THE BAHAMAS
DURING THE NEXT COUPLE OF DAYS. ESTIMATED MINIMUM CENTRAL
PRESSURE IS 1003 MB. MAXIMUM SUSTAINED WIND SPEED IS 35 KT WITH
GUSTS TO 45 KT. PLEASE SEE THE LATEST NHC FORECAST/ADVISORY
UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC AND/OR THE PUBLIC
ADVISORY MIATCPAT3/WTNT33 KNHC FOR MORE DETAILS. HANNA IS
INTERACTING WITH AN UPPER-LEVEL LOW TO THE WEST THAT IS
PROVIDING A SHEARED ENVIRONMENT LIMITING ITS SHORT TERM
INTENSIFICATION. THIS UPPER-LEVEL LOW IS FORECAST TO MOVE
WESTWARD AND WILL PROVIDE HANNA WITH A MORE FAVORABLE ENVIRONMENT
TO BECOME A HURRICANE IN ABOUT 72 HOURS OR SO.

...TROPICAL WAVES...
A WELL-DEFINED TROPICAL WAVE IS LOCATED NEAR THE WEST COAST OF
AFRICA EAST OF DAKAR SENEGAL AND IS EMERGING INTO THE EXTREME
TROPICAL ERN ATLANTIC. IT WILL BE ADDED TO THE 29/0000 UTC
SURFACE ANALYSIS. GRADUAL DEVELOPMENT OF THIS SYSTEM IS POSSIBLE
DURING THE NEXT COUPLE OF DAYS AS IT MOVES WESTWARD AT ABOUT
10-15 KT. A BROAD CYCLONIC CIRCULATION IS OBSERVED WITH
SCATTERED MODERATE/ISOLATED STRONG CONVECTION FROM 11N-16N EAST
OF 18W TO THE AFRICAN COAST.

A TROPICAL WAVE IS ALONG 38W FROM 12N TO 21N WITH A 1009 MB LOW
ALONG THE WAVE AXIS AT 17.5N MOVING W AT 10 KT. DEEP CONVECTION
IS NEARLY VOID WITH ONLY SPARSE SCATTERED SHOWERS WITHIN 150 NM
IN THE NRN SEMICIRCLE OF THE ASSOCIATED LOW PRESSURE. ANY
DEVELOPMENT OF THIS SYSTEM DURING THE NEXT COUPLE OF DAYS WILL
BE SLOW TO OCCUR.

A TROPICAL WAVE IS ALONG 53W S OF 13N MOVING W NEAR 10-15 KT. A
VERY WEAK LOW-LEVEL BROAD CYCLONIC TURNING IS OBSERVED ON
SATELLITE IMAGERY BUT DEEP VERTICAL MOISTURE AND CONVECTION ARE
ABSENT WITH THE WAVE.

...THE ITCZ...
THE ITCZ AXIS IS ANALYZED ALONG 11N14W 10N19W 16N29W 16N35W
13N40W 8N51W 8N55W 8N61W. OTHER THAN CONVECTION ASSOCIATED WITH
TROPICAL WAVE EMERGING OFF THE W AFRICAN COAST...CLUSTERS OF
SCATTERED MODERATE CONVECTION IS WITHIN 150 NM OF A LINE FROM
7N18W TO 12N32W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER TROUGH DISSECTS THE GULF OF MEXICO FROM NW FLORIDA TO
THE YUCATAN PENINSULA WHILE AN UPPER ANTICYCLONE IS CENTERED
OVER THE NW CARIBBEAN SEA. DRY UPPER AIR IS NOTED N OF 24N TO
THE W OF THE UPPER TROUGH...AND IS SUPPRESSING CONVECTION TO
ONLY A FEW SHOWERS OVER THE S CENTRAL GULF. A WEAK SURFACE RIDGE
ENCOMPASSES THE NRN GULF WATERS WHILE A 1008 MB LOW CENTERED
OFFSHORE OF VERACRUZ MEXICO NEAR 19N96W IS TRIGGERING SCATTERED
MODERATE TO STRONG CONVECTION ACROSS THE SW GULF FROM 21N-25N
BETWEEN 92W-97W. ELSEWHERE SCATTERED SHOWERS AND THUNDERSTORMS
ARE ACROSS THE CENTRAL FLORIDA PENINSULA IN ASSOCIATION WITH AN
UPPER DIFFLUENT PATTERN LOCATED EAST OF THE UPPER TROUGH ACROSS
THE CENTRAL GULF.

CARIBBEAN SEA...
AN UPPER TROUGH ENTERS THE CARIBBEAN SEA THROUGH THE MONA
PASSAGE TO SOUTH OF JAMAICA. AN UPPER ANTICYCLONE IS CENTERED
OVER THE NW CARIBBEAN. AN UPPER RIDGE EXTENDS SW OVER THE SE
CARIBBEAN ALONG THE NRN COAST OF SOUTH AMERICA. TROPICAL STORM
GUSTAV IS UNDER THE WRN EDGE OF THE UPPER TROUGH AXIS AND WILL
CONTINUE MOVING W FURTHER AWAY FROM INFLUENCE OF LAND...AND
EVENTUALLY UNDER THE INFLUENCE OF THE NW CARIBBEAN UPPER
ANTICYCLONE...WHICH WILL PROVIDE FOR A MORE FAVORABLE
ENVIRONMENT AND CONTINUED DEVELOPMENT. SCATTERED MODERATE TO
STRONG CONVECTION IS ACROSS PANAMA EXTENDING 100 NM OFFSHORE IN
THE FAR SW CARIBBEAN DUE TO THE PROXIMITY OF THE ITCZ. SIMILAR
AREAS OF CONVECTION ARE ACROSS CENTRAL AMERICA FROM VILLAHERMOSA
MEXICO SE TO CENTRAL NICARAGUA AND COSTA RICA. A FEW SCATTERED
SHOWERS ARE ALSO NOTED OVER THE LESSER ANTILLES THIS EVENING.

ATLANTIC OCEAN...
A SERIES OF UPPER LEVEL FEATURES DOMINATE THE SUBTROPICAL N
ATLANTIC. AN UPPER RIDGE EXTENDS NE FROM THE NW CARIBBEAN TO
BEYOND 31N76W WITH CONVECTION ENHANCED ACROSS THE CENTRAL
FLORIDA PENINSULA FROM FORT MYERS NE TO OVER THE W ATLC NEAR
29N80W. ANOTHER UPPER ANTICYCLONE IS NEAR 29N67W WITH A FEW
SHOWERS NOTED ALONG THE NRN PERIPHERY OF A SURFACE TROUGH THAT
EXTENDS FROM 24N73W TO 30N70W. A CUT-OFF UPPER LOW IS N OF
PUERTO RICO CENTERED NEAR 22N66W GENERATING ISOLATED SHOWERS
FROM 21N-25N BETWEEN 62W-66W AND OVER THE ERN GREATER ANTILLES
INCLUDING PUERTO RICO AND THE VIRGIN ISLANDS. AN UPPER RIDGE
LOCATED OVER T.S. HANNA IS PROVIDING GOOD OUTFLOW ALOFT MAINLY
TO THE N AND E OF THE CYCLONE. A SECOND WEAKENING UPPER LOW IS
OVER THE N/CENTRAL ATLC CENTERED NEAR 32N43W AND EXTENDS
TROUGHING S TO 22N. AN E-W UPPER RIDGE COVERS THE ERN ATLC ALONG
24N TO 40W. AT THE SURFACE...A BROAD SURFACE RIDGE REMAINS OVER
THE ATLC N OF 25N E OF 50W ANCHORED BY A 1028 MB HIGH W OF THE
AZORES.


$$
HUFFMAN


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