[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 201740
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT MON 20 SEP 2004

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN
SECTIONS OF SOUTH AMERICA...AND ATLC OCEAN TO THE AFRICAN
COAST FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION
IS BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...
RADAR...AND METEOROLOGICAL ANALYSIS.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1745 UTC.

...SPECIAL FEATURES...

TROPICAL STORM JEANNE IS CENTERED NEAR 26.8N 71.5W AT 20/1500
UTC. JEANNE IS MOVING NORTH AT 6 KT. MAXIMUM SUSTAINED WIND
SPEED IS 55 KT WITH GUSTS TO 65 KT. ESTIMATED MINIMUM CENTRAL
PRESSURE IS 990 MB. SEE LATEST NHC PUBLIC ADVISORY OR NHC
FORECAST/ ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT1/WTNT31 KNHC
OR MIATCMAT1/ WTNT21 KNHC FOR MORE DETAILS. CONVECTION NOW IN
ALL QUADRANTS BUT SHOWS LITTLE IN THE WAY OF FURTHER
ORGANIZATION. SCATTERED MODERATE CONVECTION IS WITHIN 60 NM OF
OF THE CENTER IN THE SE QUADRANT. SCATTERED MODERATE/ISOLATED
STRONG CONVECTION IS WITHIN 120 NM OF OF CENTER. UPPER LEVEL
OUTFLOW IS GOOD MOSTLY TO THE N OF THE SYSTEM BUT IS SEVERELY
LIMITED TO THE S AS MODERATE SUBSIDENCE/DRY AIR  BEING DRAWN
ACROSS THE S BAHAMAS INTO JEANNE.

HURRICANE KARL IS CENTERED NEAR 17.9N 46.3W AT 20/1200 UTC
MOVING WEST-NORTHWEST AT 9 KT. MAXIMUM SUSTAINED WIND SPEED IS
105 KT WITH GUSTS TO 130 KT. ESTIMATED MINIMUM CENTRAL PRESSURE
IS 955 MB. SEE LATEST NHC FORECAST/ ADVISORY UNDER AWIPS/WMO
HEADER MIATCMAT2/WTNT22 KNHC FOR MORE DETAILS. KARL REMAINS A
POWERFUL HURRICANE.  SOME VERTICAL SHEAR HAS STARTING TO IMPACT
THE SW SIDE QUADRANT.

TROPICAL DEPRESSION THIRTEEN HAS BEEN UPGRADED TO TROPICAL STORM
LISA AT 1200 UTC. LISA IS CENTERED NEAR 13.6N 35.9W AT 20/1500
UTC. LISA IS MOVING WEST AT 10 KT. MAXIMUM SUSTAINED WIND SPEED
IS 50 KT WITH GUSTS TO 60 KT. ESTIMATED MINIMUM CENTRAL PRESSURE
IS 998 MB. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO
HEADER MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS. LISA IS A FAIRLY
COMPACT SYSTEM WITH ASSOCIATED SCATTERED MODERATE/ISOLATED
STRONG CONVECTION WITHIN 60/75 NM OF LINE FROM CENTER OF
CIRCULATION.  LISA HAS BECOME BETTER ORGANIZED OVER THE LAST FEW
HOURS AND ADDITIONAL STRENGTHENING IS POSSIBLE OVER THE NEXT 24
HOURS.

...TROPICAL WAVES...

NONE.

...ITCZ...

ITCZ AXIS EXTENDS ALONG 10N10W 07N30W 7N41W 8N60W. CLUSTERS OF
SCATTERED MODERATE CONVECTION ARE FROM 4N-12N BETWEEN 10W-16W
AND FROM 2N-12N E BETWEEN 23W-34W.

...DISCUSSION...

GULF OF MEXICO...
A PATTERN THAT IS VERY TYPICAL TO THE LATE FALL PATTERN REMAINS
OVER THE GULF WITH A STRONG MID/UPPER LEVEL TROUGH EXTENDING
FROM THE CANADIAN MARITIMES THROUGH THE W ATLC ACROSS NE FLORIDA
TO THE SE GULF OVER THE YUCATAN PENINSULA. A SURFACE COLD FRONT
ENTERS THE REGION FROM  NORTH OF 30N ALONG 28N80W 26N85W
29N90W.  WIDELY SCATTERED MODERATE CONVECTION JUST AHEAD OF THE
FRONT.  A SURFACE TROUGH EXTEND TO THE SW FROM A 1009 MB LOW
NEAR 27N79W TO JUST SOUTH OF THE KEY WEST. WIDELY SCATTERED
SHOWERS/ISOLATED THUNDERSTORMS ALONG TROUGH AXIS.  STRONG
SUBSIDENCE AND DRY AIR DOMINATES MUCH OF THE GULF OF MEXICO.  W
GULF...A HIGH AMPLITUDE MID/UPPER LEVEL HIGH IS OVER NW MEXICO
WITH A RIDGE EXTENDING ACROSS THE CENTRAL UNITED STATES INTO
CANADA. ASSOCIATED STRONG N FLOW AROUND THE E PERIPHERY OF THE
RIDGE PREVAILS W OF 90W WITH THE ONLY SIGNIFICANT WEATHER OF
NOTE BEING WIDELY SCATTERED SHOWERS/ ISOLATED THUNDERSTORMS OVER
THE BAY OF CAMPECHE S OF 21N. THE E GULF TROUGH IS EXPECTED TO
CONTINUE TO AMPLIFY TO THE W THEN SW AS THE RIDGE OVER MEXICO
BUILDS OVER THE NE UNITED STATES.

CARIBBEAN SEA...
WEAK MID/UPPER LEVEL TROUGH EXTENDS FROM OVER THE BAHAMAS SE TO
JUST S OF JEANNE. SCATTERED MODERATE CONVECTION ALONG THE TROUGH
AXIS. OVER THE CARIBBEAN... BROAD ANTICYCLONIC FLOW COVERS
THE CARIBBEAN WITH NE FLOW E OF LINE FROM PUERTO RICO SW TO N
CENTRAL COLOMBIA USHERING IN MODERATE SUBSIDENCE/DRY AIR OVER
THE E CARIBBEAN INCLUDING THE LEEWARD AND WINDWARD ISLANDS. THE
EAST TO NORTHEAST FLOW OVER THE REMAINDER OF THE CARIBBEAN.
WIDELY SCATTERED CONVECTION ASSOCIATED WITH THE ITCZ OVER
VENEZUELA COAST FROM 7N-11N BETWEEN 74W-79W  CLUSTERS OF
SCATTERED SHOWERS/THUNDERSTORMS DOT THE W CARIBBEAN FROM
712W-83W. THIS SCENARIO WILL REMAIN  WITH A BROAD MID/UPPER
LEVEL HIGH FORMING IN THE NE CARIBBEAN NEAR 17N71W.

SUBTROPICAL ATLANTIC...
STRONG MID/UPPER LEVEL TROUGH CONTINUES TO PUSH E OVER THE W
ATLC FROM THE CANADIAN MARITIMES N OF THE REGION COURTESY OF THE
UPPER LEVEL HIGH ASSOCIATED WITH T.S. JEANNE. JEANNE IS SITUATED
BENEATH A WELL-DEFINED UPPER LEVEL HIGH WITH RIDGE EXTENDING NE
TO BEYOND 33N61W. FURTHER EAST...AMPLIFYING MID/UPPER LEVEL
TROUGH ENTERS AREA ALONG 30N53W S TO 19N54W. MID/UPPER LEVEL
MOISTURE AND HIGH CLOUDINESS COVERS THE CENTRAL/WESTERN ATLC N
OF 24N FROM 49W TO OVER T.S. JEANNE. A HIGH AMPLITUDE MID/UPPER
LEVEL RIDGE EXTENDS FROM OVER KARL N ALONG 41W COVERING THE AREA
WITH ANTICYCLONIC FLOW FROM 31W TO 50W. THE MID/UPPER LEVEL
TROUGH COVERS THE REMAINDER OF THE E ATLC WITH A SERIES OF
MID/UPPER LEVEL LOWS CENTERED NEAR 23N27W...OVER THE CANARY
ISLANDS NEAR 20N15W...AND A THIRD N OF THE REGION NEAR 36N28W.
AT THE SURFACE...

TROPICAL ATLANTIC...
ASIDE FROM ACTIVITY ASSOCIATED WITH HURRICANE KARL AND TROPICAL
STORM LISA.  MID/UPPER LEVEL RIDGING WHICH TYPICALLY EXTENDS E/W
ACROSS THE AREA IS DISRUPTED BY KARL AND TROPICAL STORM LISA. A
WEAK RIDGE LIES JUST S OF THE CAPE VERDE ISLANDS ALONG 12N/13N
WHILE A WEAK UPPER TROUGH LIES W OF KARL FROM TRINIDAD/TOBAGO TO
16N51W.

$$
JP/LL


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