[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 281801
TWDAT

TROPICAL WEATHER DISCUSSION...
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURES...
TROPICAL STORM GUSTAV IS CENTERED NEAR 17.9N 76.2W AT 28/1800
UTC OR ABOUT 35 NM EAST OF KINGSTON JAMAICA AND ABOUT 290 NM
EAST-SOUTHEAST OF GRAND CAYMAN MOVING WEST AT 4 KT. MINIMUM
CENTRAL PRESSURE IS 983 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 VERY CLOSE TO JAMAICA. IT IS NOT CLEAR IF THE CENTER
WILL PASS DIRECTLY OVER JAMAICA OR WILL HUG THE SOUTH OR NORTH
COAST...BUT WITH A WEAK MID-LEVEL RIDGE OVER FLORIDA...ALL MODELS
FORECAST GUSTAV TO CONTINUE GENERALLY WESTWARD FOR THE NEXT DAY
OR SO. GUSTAV COULD BECOME A HURRICANE BEFORE MOVING OVER
JAMAICA THIS AFTERNOON AND TONIGHT. MODERATE TO STRONG
CONVECTION IS FROM 15N-19.5N BETWEEN 74W-77.5W INCLUDING THE
EAST PORTION OF JAMAICA. 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 TODAY...WITH AN
ADDITIONAL 1 TO 2 INCHES OF RAINFALL POSSIBLE.

AT 28/1500 UTC...T.D. EIGHT IS UPGRADED TO TROPICAL STORM HANNA.
AT THIS TIME...ITS CENTER IS EXPOSED TO THE W OF THE
CONCENTRATED CONVECTION NEAR 20.5N 57.2W OR ABOUT 265 NM
NORTHEAST OF THE NORTHERN LEEWARD ISLANDS MOVING WEST-NORTHWEST
AT 11KT. A TURN TOWARD THE NORTHWEST IS EXPECTED LATER TODAY.
ON THE FORECAST TRACK...HANNA 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 1002 MB. MAXIMUM SUSTAINED WIND SPEED IS 30
KT WITH GUSTS TO 40 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 LIMITING ITS INTENSIFICATION. THE FORECAST CALLS
FOR HANNA 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 AND IS ABOUT TO EMERGE OVER THE EXTREME TROPICAL EASTERN
ATLANTIC. GRADUAL DEVELOPMENT OF THIS SYSTEM IS POSSIBLE DURING
THE NEXT COUPLE OF DAYS AS IT MOVES WESTWARD AT ABOUT 15 MPH. AN
ASCAT PASS FROM AROUND 1115 UTC SHOWED A BROAD CYCLONIC
CIRCULATION FROM 10N-15N EAST OF 20W TO THE AFRICAN COAST.

A TROPICAL WAVE IS ALONG 38W FROM 05N TO 21N WITH A 1009 MB LOW
ALONG THE WAVE AXIS AT 17N. THE PARENT WAVE HAS MOVED W AT 15 KT
OVER THE PAST 24 HOURS. SCATTERED MODERATE AND ISOLATED STRONG
CONVECTION IS FLARING WITHIN 150 NM OF THE N SEMICIRCLE OF THE
ASSOCIATED LOW PRES. SOME SLOW DEVELOPMENT OF THIS SYSTEM IS
POSSIBLE DURING THE NEXT COUPLE OF DAYS

A TROPICAL WAVE IS S OF 13N ALONG 52.5W AND HAS MOVED W ABOUT 15
KT OVER THE PAST 24 HOURS. ONLY A FEW SHOWERS ARE ENHANCED ALONG
09N E OF THE WAVE AXIS...BUT BROAD CYCLONIC TURNING IS NOTED.

...THE ITCZ...
THE ITCZ AXIS IS ANALYZED ALONG 10N14W TO 10N19W THEN BECOMES
ILL-DEFINED AS THE TROPICAL WAVE STRETCHES THE ITCZ NORTHWARD
TO NEAR 15N AT 47W. THE AXIS THEN RETURNS SW ALONG 10N43W TO
THROUGH THE WAVE AT 08N52.5W...THEN CONTINUES W AND INLAND S
AMERICA AT 07N. CONVECTION IS ENHANCED...SCATTERED MODERATE AND
ISOLATED STRONG...WITHIN 120 NM S AND SW OF THE ITCZ AXIS TO THE
E OF 32W. ONLY ISOLATED MODERATE CONVECTION ALONG THE THE AXIS
BETWEEN 40W AND 55W.

...DISCUSSION...

GULF OF MEXICO...
AN UPPER TROUGH DISSECTS THE GULF OF MEXICO FROM NW FLORIDA TO
THE BAY OF CAMPECHE WHILE AN UPPER ANTICYCLONE IS CENTERED OVER
THE CAYMAN ISLANDS. DRY UPPER AIR IS NOTED N OF 23N TO THE W OF
THE UPPER TROUGH...AND IS SUPPRESSING CONVECTION TO ONLY A FEW
SHOWERS OVER THE N CENTRAL GULF. A SURFACE RIDGE EXTENDS W
ACROSS THE NORTHERN WATERS. THE NORTHERN EXTENSION OF A TROPICAL
WAVE OVER THE E PACIFIC SPAWNED A LOW PRES OVER THE BAY OF
CAMPECHE NEAR 20N94W ESTIMATED AT 1007 MB. INTENSE CONVECTION
HAS EXPLODED WITHIN 100 NM OF 19N95W WITH NUMEROUS LIGHTNING
STRIKES. A COUPLE OF UNCONTAMINATED WIND BARS IN THE 30-35 KT
RANGE ARE NOTED ON AN EARLIER QSCAT PASS OVER THE BAY OF
CAMPECHE. SOME OF THE DEBRIS MOISTURE IS SPREADING NE WITHIN 90
NM EITHER SIDE OF LINE 21N91W TO 30N82W.

CARIBBEAN SEA...
AN UPPER TROUGH ENTERS THE CARIBBEAN THROUGH THE MONA PASSAGE
TO NICARAGUA. AN UPPER ANTICYCLONE IS CENTERED OVER THE CAYMAN
ISLANDS. AN UPPER RIDGE EXTENDS SW OVER THE SE CARIBBEAN.
CURRENTLY TROPICAL STORM GUSTAV IS UNDER THE UPPER TROUGH AXIS
AND WILL LATER MOVE W FURTHER AWAY FROM INFLUENCE OF LAND...AND
EVENTUALLY UNDER THE INFLUENCE OF THE CAYMAN UPPER
ANTICYCLONE...WHICH A MORE FAVORABLE ENVIRONMENT FOR CONTINUED
DEVELOPMENT. A LINE OF SCATTERED MODERATE AND ISOLATED STRONG
CONVECTION...IS ALONG 15N TO THE W OF 79W...AND EXTENDS NW TO
NEAR THE YUCATAN CHANNEL. A FEW SHOWERS ARE ALSO NOTED OVER THE
EXTREME NE CARIBBEAN ISLANDS.

ATLANTIC OCEAN...
A SERIES OF UPPER LEVEL FEATURES DOMINATE THE SUBTROPICAL N
ATLANTIC. AN UPPER RIDGE EXTENDS NE FROM THE NW CARIBBEAN TO
BEYOND 31N77W WITH CONVECTION ENHANCED ALONG A LINE FROM 29N76W
TO 32N77W. ANOTHER UPPER ANTICYCLONE IS NEAR 29N70W WITH A FEW
SHOWERS NOTED ALONG THE ITS NE PERIPHERY AT 29N67W. AN UPPER
TROUGH EXTENDS SW ALONG 32N62W INTO AN UPPER CYCLONE AT 22N65W.
CONVECTION IS ENHANCED E OF THE UPPER TROUGH FROM 28N62W TO
BEYOND 31N58W. WEAK UPPER RIDGING IS NOTED NEAR TROPICAL STORM
HANNA WITH THE DEBRIS MOISTURE FROM THE CYCLONE FANNING OUT OVER
THE TROPICS WITHIN 180 NM EITHER SIDE OF LINE 14N57W TO 23N57W.

A LARGE UPPER ANTICYCLONE IS NOTED OVER THE E ATLANTIC NEAR
22N26W AND IS SEPARATED FROM THE W ATLANTIC UPPER FEATURES BY AN
UPPER TROUGH LYING ALONG 31N18W TO 22N22W TO 12N22W. AT THE
SURFACE A 1030 MB HIGH PRESSURE IS CENTERED N OF THE AREA AT
38N30W WITH A RIDGE EXTENDING SW TO NEAR 27N54W.


$$
RUBIO/NELSON






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