[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 271009
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT THU SEP 27 2007

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN
SECTIONS OF SOUTH AMERICA...AND THE 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0945 UTC.

...SPECIAL FEATURES...

TROPICAL STORM KAREN HAS WEAKENED SLIGHTLY OVER THE OPEN WATERS
OF THE CENTRAL ATLANTIC. AT 27/0900 UTC KAREN WAS NEAR 13.6N
46.6W OR ABOUT 840 NM EAST OF THE WINDWARD ISLANDS...MOVING W-NW
AT 13 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 998 MB. MAXIMUM
SUSTAINED WINDS ARE 55 KT WITH GUSTS TO 65 KT. SEE LATEST NHC
FORECAST ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC
AND THE PUBLIC ADVISORY UNDER MIATCPAT2/WTNT32 KNHC FOR MORE
DETAILS. MODERATE TO STRONG SOUTHWESTERLY SHEAR AHEAD OF A
MID-OCEANIC TROUGH IS AFFECTING KAREN AND THIS SHEAR IS EXPECTED
TO PERSIST OVER THE NEXT FEW DAYS. THUS...FURTHER WEAKENING IS
EXPECTED. MODERATE CONVECTION IS MOSTLY DISPLACED NE OF THE
CENTER FROM 13N-17N BETWEEN 41W-46W. THE CENTER OF KAREN IS JUST
S OF NOAA BUOY 41041...WHICH RECENTLY REPORTED A GUST FROM THE E
AT 47 KT. SEAS AT THIS BUOY HAVE STAYED IN THE 20 TO 23 FT RANGE
OVER THE LAST FEW HOURS...AND COULD EVEN BE A FEW FEET HIGHER A
LITTLE FURTHER S CLOSER TO THE CORE. A MODERATE TO STRONG LONGER
PERIOD E SWELL WILL RACE AHEAD OF KAREN AND AFFECT EAST EXPOSED
BEACHES OF THE LESSER ANTILLES LATE FRIDAY THROUGH THE WEEKEND.

TROPICAL DEPRESSION THIRTEEN AT 27/0900 UTC WAS OVER THE SW GULF
OF MEXICO NEAR 20.8N 95.1W OR ABOUT 180 NM EAST-SOUTHEAST OF
TAMPICO MEXICO AND ABOUT 130 NM EAST OF TUXPAN MEXICO. THE
DEPRESSION IS DRIFTING W-SW NEAR 3 KT. A SLOW MOTION TO THE WEST
IS EXPECTED OVER THE NEXT 24 HOURS. ESTIMATED MINIMUM CENTRAL
PRESSURE REPORTED BY THE HURRICANE HUNTER IS 1008 MB. MAXIMUM
SUSTAINED WINDS ARE 30 KT WITH GUSTS TO 40 KT. THE DEPRESSION IS
FORECAST TO BECOME A TROPICAL STORM LATER TODAY.  SEE LATEST NHC
FORECAST ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC
AND THE PUBLIC ADVISORY UNDER MIATCPAT3/WTNT33 KNHC FOR MORE
DETAILS...INCLUDING THE LATEST WATCH AND WARNING INFORMATION.
INCREASING MODERATE CONVECTION IS MOSTLY WITHIN 120 NM SW
SEMICIRCLE. TROPICAL DEPRESSION THIRTEEN IS FORECAST TO MAKE
LANDFALL ON THE COAST OF MEXICO IN ABOUT 36 HOURS...AND IS
EXPECTED TO PRODUCE TOTAL RAINFALL ACCUMULATIONS OF 5 TO 10
INCHES OVER THE MEXICAN STATE OF VERACRUZ...WITH POSSIBLE
ISOLATED MAXIMUM AMOUNTS OF 15 INCHES.

...TROPICAL WAVES...

A TROPICAL WAVE IS OVER THE E ATLC AND CAPE VERDE ISLANDS ALONG
24W SOUTH OF 17W MOVING W 10-15 KT. THE WAVE SHOWS UP WELL IN
LOW LEVEL SATELLITE DERIVED WINDS AND VORTICITY...AND THE UW
CIMSS TPW PRODUCTS. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS WITHIN 180 NM EITHER SIDE OF AXIS...MAINLY FROM
10N-14N. THIS WAVE HAS BECOME A LITTLE BETTER ORGANIZED THIS
MORNING...AND SOME SLOW DEVELOPMENT OF THIS SYSTEM IS POSSIBLE
OVER THE NEXT COUPLE OF DAYS.

A TROPICAL WAVE IS OVER THE CARIBBEAN AND SW NORTH ATLC ALONG
71W S OF 23N MOVING W 10-15 KT. SCATTERED SHOWERS/ISOLATED TSTMS
ARE WITHIN 300 NM EITHER SIDE OF THE WAVE AXIS N OF
14N....AFFECTING THE NORTH CENTRAL CARIBBEAN N THROUGH THE TURKS
AND CAICOS. THE CLUSTER OF MODERATE TO STRONG CONVECTION
AFFECTING HISPANIOLA LAST NIGHT HAS DIMINISHED. UPPER-LEVEL
WINDS ARE NOT FAVORABLE FOR DEVELOPMENT OF THIS SYSTEM. THE
ASSOCIATED SHOWER ACTIVITY IS EXPECTED SPREAD INTO ERN CUBA AND
JAMAICA THROUGH FRIDAY.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 9N13W 11N22W 7N31W 13N41W 4N55W.
BESIDES FOR THE ACTIVITY ASSOCIATED WITH T.S. KAREN AND THE
TROPICAL WAVE OVER THE E ATLC...SCATTERED MODERATE CONVECTION IS
NEAR THE COAST OF AFRICA WITHIN 90 NM EITHER SIDE OF THE AXIS E
OF 17W...AND BETWEEN 31W-36W.

DISCUSSION...

GULF OF MEXICO...
THE MAIN WEATHER FEATURE ACROSS THE GULF OF MEXICO IS TROPICAL
DEPRESSION THIRTEEN LOCATED IN THE SW PORTION. A TROPICAL STORM
WATCH REMAINS IN EFFECT FOR THE COAST OF MEXICO FROM PALMA SOLA
TO LA CRUZ. SEE SPECIAL FEATURES ABOVE FOR DETAILS. THE SFC LOW
S OF KEY WEST YESTERDAY HAS WEAKENED...AND A NEW LOW MAY BE
FORMING OFFSHORE CENTRAL FLORIDA IN THE WRN ATLC. SEE THAT
SECTION BELOW FOR DETAILS. DRIER AIR IS FILTERING INTO THE E
GULF IN WAKE OF THE DEEP LAYER TROUGHING OVER THE FLORIDA
PENINSULA. IN FACT...BESIDES FOR T.D. 13 OVER THE FAR SW
PORTION...THE GULF IS PRETTY TRANQUIL THIS MORNING WITH A WEAK
SFC PRES GRADIENT N OF 23N AND ABUNDANT NLY FLOW ALOFT BETWEEN
RIDGING BUILDING INTO THE WRN PORTION AND THE TROUGHING OVER
FLORIDA.

CARIBBEAN SEA...
A TROPICAL WAVE IS MOVING WWD ACROSS THE CENTRAL CARIBBEAN. THE
WAVE...COUPLED WITH A DIFFLUENT PATTERN ALOFT IS GENERATING
WIDELY SCATTERED MODERATE CONVECTION N OF 14N BETWEEN 65W-79W.
SIMILAR TO YESTERDAY MORNING...SCATTERED TSTMS ARE JUST OFFSHORE
THE COAST OF COLOMBIA FROM 11N-13N BETWEEN 74W-78W. ISOLATED
TSTMS ARE S OF CUBA/N OF 15N BETWEEN 77W-82W...NEAR THE BASE OF
THE MID TO UPPER TROUGH EXTENDING S FROM FLORIDA/WRN ATLC.
TRADES REMAIN LIGHT TO MODERATE ACROSS THE BASIN...BUT
WINDS/SEAS COULD BE HIGHER AT TIMES NEAR SQUALLS ASSOCIATED WITH
THE TROPICAL WAVE. ELSEWHERE ALOFT...A LARGE UPPER HIGH IS S OF
HISPANIOLA SUPPORTING ABUNDANT TROPICAL MOISTURE E OF 78W.

ATLANTIC OCEAN...
A SFC TROUGH IS OVER THE WRN ATLC EXTENDING FROM THE STRAITS OF
FLORIDA TO THE SOUTH CAROLINA COAST. THIS IS GENERATING A LARGE
AREA OF CLOUDINESS AND SHOWERS OVER THE WRN ATLC BETWEEN
75W-80W...WITH LIGHTNING DATA DEPICTING MOST OF THE TSTM
ACTIVITY CONCENTRATED OVER AND JUST NE OF THE NW BAHAMAS. A NEW
AREA OF LOW PRESSURE COULD BE DEVELOPING OFF THE FLORIDA
EAST-CENTRAL COAST...AND SLOW DEVELOPMENT OF THIS SYSTEM IS
POSSIBLE DURING THE NEXT COUPLE OF DAYS AS IT MOVES
NORTHEASTWARD. UPPER FLOW REMAINS VERY DIFLUENT OVER THIS AREA
BETWEEN TROUGHING THROUGH FLORIDA AND RIDGING EXTENDING N FROM
THE CARIBBEAN ALONG 69W. THIS UPPER DIFFLUENCE IS ALSO
SUPPORTING SCATTERED SHOWERS AND ISOLATED TSTMS NEAR THE NRN
PORTION OF THE CENTRAL CARIBBEAN TROPICAL WAVE BETWEEN 66W-74W.
THE REMAINDER OF THE CENTRAL ATLC IS DOMINATED BY A SFC TROUGH
ENTERING THE AREA NEAR 32N33W AND CONTINUING SW TO 23N44W. THE
TROUGH IS AHEAD OF A COLD FRONT CLIPPING THE AREA ALONG 32N39W
27N54W 29N63W. THE TROUGH AND FRONT APPEAR TO BE MERGING WITH IT
BECOMING DIFFICULT TO LOCATE TWO SEPARATE BOUNDARIES. THE
COMBINED EFFECT IS PRODUCING SCATTERED SHOWER ACTIVITY FROM
20N-27N BETWEEN 42W-60W. MODERATE SFC RIDGING REMAINS ANCHORED
OVER THE E ATLC...PRODUCING LIGHT TO MODERATE NE TRADES E OF
30W. THE UPPER LOW THAT HAS BEEN AFFECTING THE FAR NE PORTION OF
THE DISCUSSION AREA THE LAST FEW DAYS IS NOW E OF THE MADEIRA
ISLANDS NEAR 32N15W. SHOWER ACTIVITY HAS MOSTLY DIMINISHED WITH
THIS UPPER LOW...WHICH IS EXPECTED TO MOVE NE OF THE AREA WHILE
OPENING INTO A TROUGH THROUGH FRI.

$$
WILLIS




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